Inorganica Chimica Acta 410 (2014) 156–170

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Inorganica Chimica Acta

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Effect of cooperative non-covalent interactions on the solid stateheterochiral self-assembly: The concepts of isotactic and syndiotacticarrangements in coordination complex

0020-1693/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.ica.2013.10.035

⇑ Present Address: Department of Chemistry, Indian Institute of Science Educa-tion and Research Bhopal, Indore By-pass Road, Bhauri, Bhopal 462 030, MadhyaPradesh, India. Tel.: +91 942 5807692; fax: +91 755 4092392.

E-mail address: hsjena@iiserb.ac.in

Himanshu Sekhar Jena ⇑Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India

a r t i c l e i n f o

Article history:Received 1 September 2013Received in revised form 27 October 2013Accepted 31 October 2013Available online 9 November 2013

Keywords:DiastereoselectivitySelf-assemblySchiff baseCo-ordination complexNon-covalent interactions

a b s t r a c t

Solid state diastereoselective self-assembly of five copper(II) heterochiral complexes containing racemicSchiff bases L1H and L2H (where L1H = 1-((1-(2-pyridyl)ethylimino)methyl)-2-naphthol ; L2H = 2-((phe-nyl(2-pyridyl)methylimino)-methyl)phenol) in crystal engineering contexts are discussed. Complexes1–5 are synthesized using ligand L1H (1–3), L2H (4, 5), CuCl2�2H2O, Cu(ClO4)2�6H2O and co-ligands suchas N3

� or N(CN)2� and are conclusively structurally characterized. Determination of molecular structures

of 1–5 confirmed the presence of a di-copper core with an inversion center located directly between thetwo copper ions. In 1–5, within one centrosymmetric dimer one of the ligands possess R configurationwhereas other possess S configuration resulting a heterochiral dimerization of ligands around copper(II)center in chiral self-discriminating manner. The significant effects of different non-covalent interactionsand co-ligands on self-assembly of heterochiral dimers into networks are studied. The presence of p� � �pinteraction between face to face benzene-naphthalene and naphthalene-naphthalene dimers are per-ceived. The isotactic and syndiotactic arrangements of the coordination complex through non-covalentinteractions are also studied.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

From the last two decades various synthetic strategies havebeen developed to design a wide variety of Schiff bases [1] andtheir metal complexes, as they find wide applications in coordina-tion polymers [2], catalysis [3], biomimetic chemistry [4], metal or-ganic framework (MOF) [5] and molecular magnetism [6]. Schiffbases having mix N, O donor sites are subject of interest becauseof their strong chelating nature. Among the transition metal ions,copper plays domino role in human tissue and is also associatedwith many important biological activities such as cytochrome coxidase, superoxide dismutase and etc. [7]. It has been reportedthat, copper(II) complexes containing pyridine based Schiff basesshow excellent reactivity towards photocleavage of DNA, antitu-mor and cytotoxic activities [8]. Among other pyridine based Schiffbases ligands, salicylaldimines and a-hydroxynaphthaldiminesderivatives were selectively employed for the synthesis of coordi-nation complexes because they can promote chelation and provideextra stability to the metal centers.

During the last few years; a significant amount of informationrelated to the characterization of chiral Schiff bases and their com-plexes has been reported [9]. It is worthy to note that the self-assembly of coordination complexes containing chiral enantiopureligands can be predictable but in case of racemic ligands it is diffi-cult to predict [10]. Quite few information concerning the self-assembly of coordination complexes containing racemic Schiffbases are accessible. Significant results in this direction have beenestablished by Stack and co-workers, Mascharak and co-workersand Kuroda and co-workers [11–13]. Factors affecting the diaste-reoselective self-assembly of coordination complexes containingchiral and racemic N-donor ligands have been reported in the liter-ature [14]. Recently, the effect of ligand substitution on the coordi-nation stereochemistry of phenoxo bridged copper(II) complexescontaining achiral Schiff bases has been reported [15]. Furthermorethe effects of ligand geometry, bridging ligands, co-ligands andnon-covalent interactions on the solid state diastereoselectiveself-assembly of copper and zinc complexes containing racemicSchiff bases have been reported [16]. Thus, it is immense importantto gather precise knowledge on how different factors affects thecoordination stereochemistry and solid state structural self-assem-bly of racemic ligands which can find wide applications in synthe-sis of (homo- or hetero-) chiral coordination polymers,coordination networks and subsequently in synthesis of homo-or heterochiral MOF [17]. Therefore a system is presented here that

H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170 157

exhibits ligand self-discrimination based solely on chirality of theligands and adds new examples to the very scarce reported chi-ral-discrimination process.

In continuation, herein two racemic Schiff bases (L1H, and L2H;Scheme 1) are synthesized and the solid state heterochiral self-assembly of five copper complexes in crystal engineering contextsare discussed.

1.1. Syntheses

2-Benzoylpyridine, 2-hydroxy-1-naphthaldehyde, NaN(CN)2,(Aldrich, USA); CuCl2�2H2O, Cu(ClO4)2�6H2O, NaN3, hydroxylaminehydrochloride, Zn dust (Merck India Ltd) and solvents were used asreceived without further purification. (R,S)-1-(2-pyridyl)ethyla-mine, (R,S)-phenyl(2-pyridyl)methanamine, and (R,S)-phenyl(2-pyridyl)methylimino)methyl)phenol (L2H) were prepared usingour earlier reported procedure [16b,c].

1.1.1. (R, S) 2-((1-(2-pyridyl)ethylimino)methyl)naphthol (L1H)A mixture of 1-(2-pyridyl)ethylamine (1.22 g, 10.0 mmol) and

2-hydroxy-1-naphthaldehyde (1.72 g, 10.0 mmol) in methanol(60 mL) was stirred for 2 h. The solutions were evaporated to dry-ness and dried under vacuum which results reddish oil. Yield:2.62 g (95%). ESI-MS: m/z Calc. for C18H16N2O+ 277.33. Found:(M++H) 277.40. IR (KBr, cm�1): 3467(b), 3062(w), 2973(w),2925(w), 1627(s), 1595(m), 1543(w), 1520(m), 1492(m), 1434(w),1403(m), 1361(s), 1314(m), 1246(m), 1212(m), 1187(m), 1142(w),1120(w), 1066(w), 993(s), 837(m), 779(m), 749(s), 718(w),550(w), 474(m), 439(w). 400 MHz 1H NMR (d (J, Hz), CDCl3): 8.98(1H, s), 8.59 (1H, d, 6.4), 7.90 (1H, d, 8.4), 7.72 (1H, t, 4.6), 7.63(1H, d, 8.0), 7.46 (1H, d, 6.4), 7.43 (2H, t, 6.2), 7.28 (1H, d, 7.6),7.25 (2H, m), 6.96 (1H, d, 8.0), 4.89 (1H, q), 1.79 (3H, d, 6.8).100 MHz 13C NMR (d, CDCl3): 175.0, 161.0, 157.6, 149.4, 137.6,137.4, 133.7, 129.3, 128.1, 126.5, 124.2, 123.08, 123.01, 120.6,118.2, 107.2, 64.5, 22.9.

1.1.2. Synthesis of [Cu(L1)Cl]2 (1)To L1H (0.288 g, 1.0 mmol) dissolved in methanol (10 mL), solid

CuCl2�2H2O (0.300 g, 1.0 mmol) was added and stirred for 2 h. Theresulting light green solution was allowed to evaporate at roomtemperature. Light green color single crystals of 1 suitable forX-ray diffraction study were obtained from the slow evaporationfor about one week time. Yield: 0.68 g (82%). Anal. Calc. for C36H30

Cl2Cu2N4O2: C, 57.76; H, 4.04; N, 7.48. Found: C, 57.74; H, 4.01; N,7.45%. Selected IR (KBr, cm�1): 3438(b, OH), 1621(s, C@N). UV–Vis[kmax, nm (e, M� cm�1), CH3OH solution]: 638(304); 356(4456);292(8028). EPR (solid state, 298 K): g = 2.102, A = 70 G, leff/Cu(298 K), 1.84 B.M.

1.1.3. Synthesis of [Cu(L1)(N3)]2 (2)To L1H (0.226 g, 1.0 mmol) dissolved in methanol (10 mL), solid

CuCl2�2H2O (0.300 g, 1.0 mmol) was added and stirred for 10 min.To this light green solution, methanol solution of (5 mL) NaN3

(0.65 g, 1.0 mmol) was added and further stirred for another 3 h.The resulting dark green solution was filtered to remove the white

HO

NN

L2H

HO

NN

CH3

L1H

* *

Scheme 1. Racemic Schiff bases (L1H, L2H) used for study.

precipitates which might be due to the formation of NaCl on anionmetathesis and stored at room temperature for crystallization.Green colored single crystals of 2 suitable for X-ray diffractionstudy were obtained from the slow evaporation of the solutionafter one week time. Yield: 0.56 g (73%). Anal. Calc. for C36H30Cu2

N10O2: C, 56.76; H, 3.97; N, 18.39. Found: C, 56.73; H, 3.95; N,18.35%. Selected IR (KBr, cm�1): 3436(b, –OH), 2032(s, azide),1625(s, C@N). UV–Vis [kmax, nm (e, M� cm�1), CH3OH solution]:636(324); 358(5436); 292(9874). EPR (solid state, 298 K):g = 2.113, A = 71 G, leff/Cu (298 K), 1.82 B.M.

1.1.4. Synthesis of [Cu(L1)(N(CN)2)]2 (3)To L1H (0.226 g, 1.0 mmol) dissolved in methanol (10 mL), solid

CuCl2�2H2O (0.300 g, 1.0 mmol) was added and stirred for 10 min.To this light green solution, methanol solution of (5 mL) NaN(CN)2

(0.81 g, 1.0 mmol) was added and further stirred for another 3 h.The resulting solution was filtered to remove the white precipi-tates which might be due to the formation of NaCl on anionmetathesis and stored at room temperature for crystallization.Green colored single crystals of 3 suitable for X-ray diffractionstudy were obtained from the slow evaporation of the solutionon standing for about one week time. Yield: 0.58 g (70%). Anal. Calc.for C40H30Cu2N10O2: C, 59.32; H, 3.73; N, 17.30. Found: C, 59.31; H,3.71; N, 17.28%. Selected IR (KBr, cm�1): 3443(b, –OH), 2295(s),2238(s), 2182(s) (dicyanamide), 1626 (s, C@N). UV–Vis [kmax, nm(e, M�1 cm�1), CH3OH solution]: 635(357); 345(3436); 298(7688).EPR (solid state, 298 K): g = 2.110, A = 71 G, leff/Cu (298 K), 1.91B.M.

1.1.5. Synthesis of [Cu(L2)(ClO4)(H2O)] (4)Same procedure was followed for the synthesis of complex 4 by

using ligand L2H in place of L1H and using Cu(ClO4)2�6H2O in placeof CuCl2�2H2O in the same molar ratio as described for complex 1.Green colored single crystals of 4 suitable for X-ray diffractionstudy were obtained from the slow evaporation of the solution.Yield: 0.68 g (73%). Anal. Calc. for C19H17ClCuN2O6: C, 48.73; H,3.66; N, 13.57. Found: C, 48.71; H, 3.63; N, 13.54%. Selected IR(KBr, cm�1): 3449(b, –OH), 1618(s, C@N), 1090(b, perchlorate).UV–Vis [kmax, nm (e, M�1 cm�1), CH3OH solution]: 634(237);402(468); 378(6742). EPR (solid state, 298 K): g = 2.102, A = 70 G,leff/Cu (298 K), 1.88 B.M.

1.1.6. Synthesis of [Cu(L2)(N3)]2 (5)Same procedure was followed for the synthesis of complex 5 by

using ligand L2H in place of L1H in the same molar ratio as de-scribed for complex 2. Green colored single crystals of 5 suitablefor X-ray diffraction study were obtained from the slow evapora-tion of the solution. Yield: 0.40 g (75%). Anal. Calc. for C38H30Cu2

N10O2: C, 58.08; H, 3.85; N, 17.82. Found: C, 58.04; H, 3.82; N,17.79%. Selected IR (KBr, cm�1): 3449(b, –OH), 2035(s, azide),1621(s, C@N). UV–Vis [kmax, nm (e, M�1 cm�1), CH3OH solution]:636(365); 395(546); 383(5672). EPR (solid state, 298 K):g = 2.114, A = 71 G, leff/Cu (298 K), 1.91 B. M.

2. Materials and methods

A Perkin-Elmer Spectrum One spectrometer (4000–450 cm�1),Perkin–Elmer Series II CHNS/O Analyzer 2400, Perkin–Elmer Lamb-da 25 spectrometer, and Brüker 400 MHz spectrophotometer wereused for obtaining relevant data.

X-ray crystallographic data were collected using Brüker SMART

APEX-CCD diffractometer with Mo Ka radiation (k = 0.71073 Å).The intensity data were corrected for Lorentz and polarizationeffects and empirical absorption corrections was applied usingSAINT program [18,19]. All the structures were solved by direct

158 H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170

methods using SHELXS-97 [20]. Non-hydrogen atoms located fromthe difference Fourier maps were refined anisotropically by full-matrix least-squares on F2, using SHELXS-97 [20]. All hydrogen atomswere included in the calculated positions and refined isotropicallyusing a riding model. In complex 4, the perchlorate group is asusual disorder and oxygen atoms (O3, O4) exhibits positional dis-order with huge thermal parameters. Attempts to resolve the posi-tional disorder remain unsuccessful.

3. Results and discussion

3.1. Synthesis of the complexes

The mono-condensed Schiff bases (L1H and L2H) were preparedfollowing simple condensation strategy using our earlier synthe-sized chiral amines such as (R,S)-1-(2-pyridyl)ethylamine and(R,S)-phenyl(2-pyridyl)methanamine with commercial available2-hydroxy-1-naphthaldehyde and salicyldehyde in 1:1 ratiorespectively. Schiff base L1H isolates as reddish oil whereas L2Hprecipitates from reaction mixture as yellow powder. The presenceof sharp IR stretching frequencies at 1622 and 1627 cm�1 and pres-ence of singlet in 1H NMR at 8.55 and 8.98 ppm confirms the for-mation of Schiff bases respectively. The complexes weresynthesized simply by allowing the racemic Schiff bases to reactwith copper(II) salts followed by anion metathesis with azideand dicyanamide ions in 1:1:1 ratio. The mono-negative tridentateSchiff bases and the anions/co-ligands such as chloro, azide anddicyanamide ions satisfies the charge of the coordination com-plexes. All the complexes except complex 2, exhibits phenoxobridged di-copper (Cu2O2) core while complex 2 results l-1,1-azide bridged di-copper core. Such types of di-copper complexeshave great deal of importance in terms of correlating structureand magnetic properties [21]. In complexes 1–4, the axial bond isquite large due to Jahn–Teller distortion. Such distorted squarepyramidal complexes having long axial bonds finds application inMOF and acts as attractive building blocks proposing weak axialbinding and coordination versatility [22].

Meanwhile although non-covalent forces are weaker than thecoordinate bonds, they are common and play critical roles in form-ing the supramolecular structures due to their significant contribu-tion to the self-assembly process. In addition they plays importantrole in biological systems and direct the physicochemical proper-ties of molecular systems in the solid state. Thus their explorationand understanding in the supramolecular systems is essential forcrystal engineers who design structures, in particular those ofmaterials based on coordination complexes with organic ligands.Among the non-covalent interactions, H-bonding is the mostwidely used synthons over other and can able to generate flexiblematerials which are more elastic in nature. Among the other typesof non-covalent interactions, p� � �p stacking between the aromaticrings are used in construction of flexible materials. Therefore theintention of using p electrons rich naphthalene derivatives wasto explore the effect of p� � �p stacking on the diastereoselectiveself-assembly of coordination complexes. Although several intelli-gence of crystal engineering approach on the formation and controlof coordination complexes are reported [23], none of them discussabout their diastereoselective nature i.e. what will be their selec-tivity when a particular system contains racemic ligand. For exam-ple if a coordination complex contains chiral enantiopure ligandthe possible non-covalent interactions interlinks only the enantio-pure moieties. But the outcomes are more complicated if the coor-dination complex contains racemic ligands i.e. whether thepossible non-covalent interaction interlinks two coordination com-plexes containing ligands of same chirality (homochiral) or of dif-ferent chirality (heterochiral). Hence, the key aim of the present

article is to explore the diastereoselective nature of non-covalentinteractions in coordination complexes containing racemic ligands.Furthermore different co-ligands such as chloro, perchlorate, azideand dicyanamide ions were selected with intention of investigatingtheir effect on transfer the stereochemical information from mono-mer and dimer to coordination polymers (homo- or heterochiralcoordination polymer) using their various bridging modes. It hasbeen reported that the uncoordinated nitrogen atom of azide anddicyanamide ions are often involved in intermolecular or intramo-lecular hydrogen bonding and other weak interactions to regulateand stabilize the supramolecular structures.

3.2. Crystal structures of the complexes 1–5

The molecular structures of 1–5 were determined and thecrystallographic and refinement parameters are listed in Table 1.Selected bond distances are listed in Table 2. Selected bond anglesof 1–3 and of 4 and 5 are listed in Table 3 and Table 4 respectively.The conventions followed in discussions are: L1 = 1-((1-(2-pyridyl)ethylimino)methyl)-2-naphtholate ion ; L2 = 2-((phenyl(2-pyridyl)methylimino)-methyl)phenolate ion; OP = phenolate-O; NY =pyridyl-N; NI = imine–N; OL = perchlorate-O; NZ = azide-N andND = dicyanamide–N.

3.3. Structure of [Cu2(L1)2Cl2] (1)

Complex 1 crystallized in space group P 21/c. The asymmetricunit of 1 contains binuclear copper(II) center bridged by ligandL1 in meridional fashion. It is worthy to mention that within onemolecule, one of the ligands possess R configuration whereas otherpossess S configuration resulting a heterochiral dimerization ofligand L1 around copper(II) center in chiral self-discriminating man-ner. Thus complex 1 crystalized in centrosymmetric space groupwith the inversion center located directly between the two copperions. ORTEP diagram with the atom labeling scheme of the centro-symmetric dimer having Cu2O2 unit is displayed in Fig. 1. In 1, thecoordination geometry around copper(II) centers are satisfied bytwo NPNIOP-donor set of the ligand L1 and two trans orientated ter-minal coordinated chloride ions. Thus the coordination geometryaround the five coordinated copper(II) centers can be bestdescribed as distorted square pyramidal as inferred from thecalculated s value of 0.06 [24]. In 1, the axial Cu–O1A bonddistance of 2.648(2) Å is quite longer than the usual range andsat perpendicular to the square plane formed by ligand L1. Thislong axial bond is due to the Jahn–Teller distortion and orientsalong dxz/dyz orbital than the dZ

2. The cisoid angles are lying inthe range of 81.80(7) – 99.02(4)� and the trans angles are in therange of 167.31(5)–170.96(7)�. The bond order around the coppercenter follows the trend Cu–NP > Cu–NI > Cu–OP. The Cu2O2 unitis slightly butterfly in shape having the non-bonded OP� � �OP andCu� � �Cu distances of 3.209(2) and 3.333(1) Å respectively.

The packing diagram of complex 1 consequence a 2D sheetstructure instigating from the non-classical H-bonding(C2–H2� � �Cl1 = 3.803(3) Å) interactions [25] between the ligandmoiety and the chloride ion down the a-axis as illustrated inFig. 2. It is immense important to analyze the solid state packingin terms of the diastereoselectivity. It was found that the hetero-chiral dimers are interlinked thorough non-classical H-bondinginteractions in diastereoselective manner. Hence the R isomer(brinjal color) of L1 in a particular heterochiral dimer is linked tothe S isomer (orange color) of L1 in a nearby heterochiral dimerand consequence another heterochiral dimerization through non-classical H-bonding interaction. So in present condition it can bestated that non-classical H-bonding interactions are diastereose-lective in nature (� � �RS� � �RS� � �RS� � �). Careful analysis of the afore-said 2D sheet structures down the c-axis outcomes a helical

Table 1Crystallographic and refinement parameters of 1–5.

1 2 3 4 5

Formula C36H30Cl2Cu2N4O2 C36H30Cu2N10O2 C40H30Cu2N10O2 C19H17ClCuN2O6 C38H30Cu2N10O2

CCDC number 957070 957071 957072 957073 957074Formula weight 748.64 761.80 809.84 468.35 785.80T (K) 296 (2) 296 (2) 296 (2) 296 (2) 296 (2)Wavelength (Å) 0.71073 0.71073 0.71073 0.71073 0.71073Crystal system monoclinic monoclinic monoclinic monoclinic monoclinicSpace group P 21/c P 21/c P 21/c P 21/c P 21/ca (Å) 10.0562(11 7.7875(3) 10.0141(3) 12.132(3) 8.4762(5)b (Å) 12.3701(14) 14.8276(6) 17.0497(6) 15.866(4) 11.7471(8)c (Å) 13.3316(14) 14.3676(6) 10.5311(4) 10.020(2) 17.1483(10)a (�) – – – – –b (�) 106.811(6) 91.805(3) 107.005(2) 99.431(16) 92.823(4)c (�) – – – – –V (Å3) 1587.5(3) 1658.20(12) 1719.44(10) 1902.6(7) 1705.40(18)Z 2 2 2 4 2Dcalcd (g m�3) 1.566 1.526 1.564 1.635 1.530l (mm�1) 1.549 1.333 1.290 1.329 1.299F(000) 764 780.0 828.0 956.0 804.0Reflection collected 3885 4179 4270 3846 3197Unique reflections 3171 2489 3693 2630 2274hmin, hmax(�) 2.29, 28.32 1.97, 28.43 2.13, 28.28 1.70, 26.42 2.10, 25.54Goodness-of-fit (GOF) on F2 1.031 1.021 1.001 0.999 1.001R1

a, wR2b (I P 2r(I)) 0.0287, 0.0700 0.0434, 0.0912 0.0365, 0.0905 0.0483, 0.1140 0.0405, 0.0944

R1a, wR2

b (all data) 0.0419, 0.0800 0.0844, 0.1036 0.0649, 0.1026 0.0766, 0.1279 0.0519, 0.1000Largest peak/hole (e �3) 0.378/�0.381 0.385/�0.415 0.409/�0.323 0.817/�0.653 0.328/�0.590

a R1 ¼ RkFo j � j Fck=R j Fo j :b wR2 ¼ ½RwðF2

o � F2c Þ

2=RwðF2

oÞ2�1=2:

H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170 159

structure as illustrated in Fig. 3. Recently Li et al. describedsimilar helical self-assembly of coordination complex containingachiral 40-phenyl-4,20:60,400-terpyridine ligand through non-classicalC–H� � �Cl H-bonding interactions which results racemic complexin heterochiral packing fashion [26].

3.4. Structure of [Cu2(L1)2(l-1,1-N3)2] (2)

Complex 2 crystallized in space group P 21/c. The asymmetricunit of 2 contains binuclear copper(II) center bridged by ligand

Table 2Selected bond lengths (Å) in 1–5.

1 2 3 4 5

Cu1–N1 2.016(2) 1.995(2) 2.021(2) 1.991(3) 2.120(3)Cu1–N2 1.945(2) 1.939(2) 1.917(2) 1.933(3) 2.058(3)Cu1–O1 1.921(2) 1.897(2) 1.921(1) 1.893(3) 2.093(3)Cu1–O1A 2.648(2) – 2.664(2) – 2.034(3)Cu1–N3 – 1.986(2) 1.957(2) – 1.975(4)Cu1–Cl1 2.248(1)Cu1–N3A – 2.530(2) – –Cu1–O2 – – – 2.009(3)Cu1–O3 – – – 2.525(7)Cu� � �Cu 3.333(1) 3.362(1) 3.357(1) – 3.153(1)

Table 3Selected bond angles (�) in 1–3.

1 2

N1–Cu1–N2 81.80(7) N1–Cu1–N2N1–Cu1–O1 170.96(7) N1–Cu1–O1N1–Cu1–O1A 89.37(6) N1–Cu1–N3N1–Cu1–Cl1 95.73(5) N1–Cu1–N3AN2–Cu1–O1 89.83(7) N2–Cu1–O1N2–Cu1–O1A 93.41(6) N2–Cu1–N3N2–Cu1–Cl1 167.31(5) N2–Cu1–N3AO1–Cu1–O1A 87.72(6) O1–Cu1–N3O1–Cu1–Cl1 93.18(5) O1–Cu1–N3ACl1–Cu1–O1A 99.02(4) N3–Cu1–N3ACu1–O1–Cu1A 92.28(6) Cu1–N3–Cu1A

L1 in meridional fashion. Unlike complex 1, in complex 2 thedi-copper core generates from the l-1,1-azide bridge. It was knownthat such bridging mode of azide ion engenders ferromagneticinteractions between copper centers [27]. Similar to complex 1,in complex 2 heterochiral dimerization of ligand L1 around cop-per(II) center occurs in a chiral self-discriminating manner. Hencecomplex 2 crystalizes in centrosymmetric space group with theinversion center located directly between the two copper ions inCu2(NZ)2 units. ORTEP diagram with the atom labeling scheme ofthe centrosymmetric dimer is displayed in Fig. 4. It can be statedthat complex 1 upon anion metathesis with azide ion prefers tobe in l-1,1-NZ bridge rather than OP bridge retaining the heterochi-ral dimerization of L1 around the di-copper core. In 2, the coordi-nation geometry around copper(II) centers are satisfied by twoNPNIOP-donor set of the ligand L1 and two l-1,1-NZ ions. Thuscoordination geometry around the five coordinated copper(II) cen-ters can be best described as distorted square pyramidal as inferredfrom the calculated s value of 0.08. The cisoid angles are lying inthe range of 82.54(9)–98.92(9)� and the trans angles are in therange of 170.62(9)–175.5(1)�. Since the cisoid angles are close to90� and the trans angles are close to 180� hence the ligand bindto the copper center in a square plane. Another quite longer axialCu–N3A bond (2.530(2) Å) is sat nearly perpendicular (N2–Cu1–N3A = 98.92(9)� and N3–Cu1–N3A = 84.52(9)�) to the square plane

3

82.54(9) N1–Cu1–N2 82.23(8)170.62(9) N1–Cu1–O1 172.30(8)

94.19(9) N1–Cu1–O1A 91.02(7)95.79(8) N1–Cu1–N3 95.22(9)92.43(9) N2–Cu1–O1 90.53(8)

175.5(1) N2–Cu1–O1A 90.53(8)98.92(9) N2–Cu1–N3 173.79(9)90.36(9) O1–Cu1–O1A 87.30(6)92.81(8) O1–Cu1–N3 92.24(8)84.52(9) O1A–Cu1–N3 88.25(7)95.48(9) Cu1–O1–Cu1A 92.70(7)

Table 4Selected bond angles (�) in 4 and 5.

4 5

N1–Cu1–N2 82.7(1) N1–Cu1–N2 78.6(1)N1–Cu1–O1 175.5(1) N1–Cu1–O1 163.3(1)N1–Cu1–O2 93.4(1) N1–Cu1–O1A 101.9(1)N1–Cu1–O3 97.3(2) N1–Cu1–N3 97.0(2)N2–Cu1–O1 94.3(1) N2–Cu1–O1 85.7(1)N2–Cu1–O2 168.3(1) N2–Cu1–O1A 116.7(1)N2–Cu1–O3 89.3(2) N2–Cu1–N3 155.0(1)O1–Cu1–O1A 83.5(1) N2–Cu1–N3A 121.6(1)O1–Cu1–Cl1 96.4(1) O1–Cu1–N3 112.8(1)Cl1–Cu1–O1A 92.5(1) O1–Cu1–N3A 89.0(1)O1–Cu1–O2 88.9(1) N3–Cu1–N3A 83.1(1)O1–Cu1–O3 86.1(2) Cu1–O1–Cu1A 99.6(1)

Fig. 1. ORTEP diagram (30%) and atom labeling scheme in complex 1 (All H-atomsexcept asymmetric H6 are omitted for clarity).

Fig. 3. Illustration of helical structure found in complex 1 (different colorscorresponds to different helices).

160 H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170

formed by ligand L1 and which is due to Jahn–Teller distortion. Thebond order around the copper center follows the trend Cu–NP >Cu–NZ > Cu–NI > Cu–OP. In 2 the non-bonded NZ� � �NZ and Cu� � �Cudistances are of 3.063(3) and 3.362(1) Å respectively.

Packing diagram of 2 exerts several interesting solid state struc-tural self-assembly through the cooperative non-covalent interac-tions. Since the ligand L1 exhibits naphthalene moiety, C–H� � �pand p� � �p interactions are expected due to the p cloud electronsof naphthalene ring. It is worthy to note that in 1 such types ofinteractions are absent whereas in 2 a weak C–H� � �p interactionof (C4–H4� � �C10 = 3.751(4) Å) assemble the heterochiral dimersto a rectangular non-covalent metal organic framework (MOF) or

Fig. 2. Illustration of 2D sheet instigating from the non-classical C–H� � �Cl H-bonding intligand L1 respectively). (For interpretation of the references to colour in this figure lege

supramolecular MOF in diastereoselective fashion as illustratedin Fig. 5. Thus the aforesaid C–H� � �p interaction interlinks the Risomer of L1 in a particular heterochiral dimer to the S isomer ofL1 in nearby heterochiral dimer (� � �RS� � �RS� � �RS� � �). Similarly aC–H� � �N interaction of (C13–H13� � �N5 = 3.751(4) Å) assemblesthe heterochiral dimers in diastereoselective fashion to 2D sheetstructures (Fig. 6). The aforementioned cooperative C–H���p andC–H� � �N interactions altogether results a 3D structure down the caxis where the copper and azide ions gathers in 1D fashion (Fig. 7).

3.5. Structure of [Cu2(L1)2(l-1-N(CN)2)2] (3)

Complex 3 crystallized in space group P 21/c. The asymmetricunit of 3 contains binuclear copper(II) center bridged by ligandL1 in meridional fashion. Similar to complex 1, in complex 3 the

eraction found in 1 (brinjal color and orange color corresponds to R and S isomer ofnd, the reader is referred to the web version of this article.)

Fig. 4. ORTEP diagram (30%) and atom labeling scheme in complex 2 (All H-atomsexcept asymmetric H6 are omitted for clarity).

Fig. 5. Illustration of supramolecular MOF structure found in 2 originating from aweak C–H� � �p interaction (color code same as Fig. 2).

H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170 161

di-copper core generates from the OP bridged meridional coordinat-ing ligand L1. It is vital to note that complex 1 upon anion metath-esis with azide ion (2) prefers to form l–1,1-NZ bridge di-coppercore rather than OP bridge whereas upon metathesis with dicyan-amide ion (dca) (3) it regains its OP bridged di-copper core. Thesestructural changes are due to the anion metathesis with differentsize of the anions. Since l-1,1-dicyanamide ion bridge are rarely

Fig. 6. Illustration of 2D sheet structure found in 2 originatin

observed [28], complex 3 might prefers to bridge in OP fashionrather than l-1,1-ND bridging mode. In 3, the coordination geom-etry around copper(II) centers are satisfied by two OP bridgedNPNIOP-donor set of the ligand L1 and two l-1 coordinatingdicyanamide ions oriented in trans position. Thus coordinationgeometry around the five coordinated copper(II) centers can bebest described as distorted square pyramidal as inferred from thecalculated s value of 0.024. Hence complex 3 crystalizes in centro-symmetric space group with the inversion center located directlybetween the two copper ions in Cu2(OP)2 units. ORTEP diagramwith the atom labeling scheme of the centrosymmetric dimer isdisplayed in Fig. 8. The cisoid angles are lying in the range of82.23(8)–97.43(7)� and the trans angles are in the range of172.30(8)–173.8(1)�. Similar to complexes 1 and 2, in complex 3 ci-soid angles are close to 90� and the trans angles are close to 180�hence the ligand L1 bind to the copper center in a nearly squareplane. Another quite longer axial Cu–O1A bond (2.664(2) Å) isnearly perpendicular (N2–Cu1–O1A = 97.43(7)� and N3–Cu1–O1A = 88.25(7)�) to the square plane formed by ligand L1 and isdue to Jahn–Teller distortion. In 3, ligand L1 bounds to the coppercenter by a five-membered and a six-membered chelate ring andboth rings are puckered, resulting in an envelope shape for the li-gand moiety. The asymmetric carbon atom is out of plane from thepuckered five membered rings as inferred from the dihedral anglesof 15.42� between the plane containing C5C6N2 and C5N1Cu1N2atoms. The dihedral angle of 18.05� between the planes formedby N2Cu1O1 and O1C18C9C8N2 suggests an out of plane displace-ment of copper(II) center from envelope shaped six memberedrings. The bond order around the copper center follows the trendCu–NP > Cu–ND > Cu–OP > Cu–NI. The non-bonded OP� � �OP andCu� � �Cu distances are of 3.210(2) and 3.358(1) Å respectively.

Packing diagram of 3 employs several interesting solid statestructural self-assembly through the parallel displaced [29] p� � �pinteraction between naphthalene–naphthalene face to face hetero-chiral dimer (C15� � �C17 = 3.341(4) Å; Fig. 9) and benzene-naphtha-lene dimer (C3� � �C11 = 3.296(5) Å; Fig. 10) [30]. Although there isnumerous number of p� � �p interactions between benzene–benzeneare scrutinized, the aforementioned p� � �p interaction betweennaphthalene–naphthalene and naphthalene–benzene are quitefew. It is worthy to note that in 3 such types of parallel displacedp� � �p interaction are diastereoselective in nature. As illustrated inFig. 9 and 10, the R isomer of L1 in a particular heterochiral dimeris linked to the S isomer of L1 in nearby heterochiral dimer in� � �RS� � �RS� � �RS� � � fashion through the p� � �p interactions. Thus a cen-ter of symmetry arises exactly in between the parallel displacedp� � �p interactions and hence results heterochiral dimers. The aboveobservation implies that the weak intermolecular interactions expe-rience some form of cooperativity between themselves in order to

g from C–H� � �N interaction (color code same as Fig. 2).

Fig. 7. Illustration of 3D structure found in 2 originating from cooperative C–H� � �N and C–H� � �p interactions and representing the 1D arrangement of copper and azide ions inlattice.

Fig. 8. ORTEP diagram (30%) and atom labeling scheme in complex 3 (all H-atomsexcept asymmetric H6 are omitted for clarity).

Fig. 9. Illustration of 1D structure found in 3 originating from parallel displaced p� � �between ligand moiety and dicyanamide ion (color code same as Fig. 2).

162 H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170

achieve sufficient stability for heterochiral dimerization instead ofhomochiral dimerization [31]. In addition a notably C–H� � �N inter-action of (C14–H14� � �N5 = 3.602(4) Å) between the ligand moietyand ND atoms assembles the heterochiral dimers in diastereoselec-tive fashion to form supramolecular MOF structure as illustratedin Fig. 11. The aforementioned p� � �p and C–H� � �p interactions(C2–H2� � �C12 = 3.506(5) Å) between naphthalene–benzene moietyin two nearby heterochiral dimers extends to a helical structure asillustrated in Fig. 12which further accumulates through naphtha-lene-naphthalene parallel displaced p� � �p and C–H� � �ND interac-tions to form 3D helical structure. In the 3D structure, coppercenters and dicyanamide ions are arranged in 1D fashion down thec axis (Fig. 12). The intra-chain Cu� � �Cu distances in the particularhelical structure are 8.8 and 11.3 Å and the inter-chain Cu� � �Cudistance is 10.01 Å. Similarly a C–H� � �p interactions of (C13–H13� � �C20 = 3.506(5) Å; C6–H6� � �C20 = 3.536(5) Å) and p� � �pinteraction of (C1� � �C20 = 3.378(5) Å) between ligand moiety andunsaturated dicyanamide carbon atoms (C20) assembles theheterochiral dimers to 3D structure. Careful analysis of the packingdiagram down a axis reveals a 3D structure where copper and dicy-anamide ions are located in helical fashion (Fig. 13). The intra-chainCu� � �Cu distance in the particular helical arrangement of copperand dicyanamide ions is 10.53 Å. Similar type of dicyanamide ion

p interaction between naphthalene–naphthalene dimer and C–H� � �p interactions

Fig. 10. Illustration of 1D structure found in 3 originating from diastereoselective parallel displaced p� � �p interaction between naphthalene–benzene dimer (color code sameas Fig. 2).

Fig. 11. Illustration of supramolecular metal organic framework found in 3 originating from diastereoselective C–H� � �N interaction between ligand moiety and ND atoms(color code same as Fig. 2).

H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170 163

induced helical self-assembly of copper(II) complexes containingtridentate Schiff bases has been reported recently [32].

3.6. Structure of [Cu(L2)(OH2)(ClO4)] (4)

Complex 4 crystallized in space group P 21/c. The asymmetricunit of 4 contains mononuclear copper(II) center bridged by R iso-mer of ligand L2 in meridional fashion. ORTEP diagram with theatom labeling scheme of complex 4 is displayed in Fig. 14. In 4,the coordination geometry around copper(II) centers are satisfiedby one NPNIOP-donor set of the ligand L2 and one water moleculein square plane and one axially orientated perchlorate ions. Thuscoordination geometry around the five coordinated copper(II) cen-ters can be best described as distorted square pyramidal as inferredfrom the calculated s value of 0.12. In 4, the axial Cu–OL bond dis-tance of 2.525(7) Å is quite longer than the usual range and sat per-pendicular to the square plane (O3–Cu1–N2 = 89.3(2) Å and O3–Cu1–O2 = 102.2(2) Å) formed by ligand L2. This long axial bond isdue to the Jahn–Teller distortion. It is worthy to mention thatthe mononuclear penta-coordinated copper center is linked tosymmetry opposite nearby molecule through two H-bonding inter-actions: one between OP atom of L2 and coordinated water mole-cules (O2A–H2A� � �O1 = 2.702(4) Å, (�x, �y, 1�z)) and anotherbetween OP atom of L2 and O3 of perchlorate ion(O2A–H2A� � �O5 = 2.795(5) Å, (�x, �y, 1 � z)). Thus consequencesa di-copper center through H-bonding interactions. It immense

important to note that within the dimer, one of the ligands L2 pos-sess R configuration whereas other possess S configuration result-ing a heterochiral dimerization of L2 around copper(II) center inchiral self-discriminating manner. Therefore the aforementionedH-bonding interactions can be called as diastereoselective H-bond-ing interactions. Thus complex 4 is centrosymmetric dimer withthe inversion center located directly between the two copper ionsas illustrated in Fig. 15. The cisoid angles are lying in the range of82.7(1)–102.2(2)� and the trans angles are in the range of168.3(1)–175.5(1)�. The bond order around the copper centerfollows the trend Cu–NP > Cu–NI > Cu–OP. The Cu� � �Cu distancebetween H-bonded dimer is 5.141(1) Å.

Complex 4 exerts several interesting solid state structuralself-assembly through the C–H� � �O, C–H� � �p interactions. In 4the aforementioned diastereoselective H-bonded heterochiraldimers are linked through the C–H� � �O interaction (C11–H11� � �O6 = 3.435(7)) between the OL and the ligand moiety intoa 1D structure. It is worthy to note that the aforesaid weakC–H� � �O interaction accumulates the H-bonded heterochiral dimersin ���RS���RS���RS��� fashion where the asymmetric carbon atoms areorientated in isotactic manner as shown in Fig. 16. Similarly a nota-bly weak C–H� � �O interaction between the OL and the ligand moi-ety (C9–H9� � �O4 = 3.46(1) Å) assembles the mononuclear coppercenters having exclusively either R or S isomers of L2 to 1D struc-ture as follows � � �R� � �R� � �R� � � or � � �S� � �S� � �S� � �. Thus the resulted 1Dchain can be called as homochiral 1D chain of exclusively R isomers

Fig. 12. Illustration of 3D helical arrangement of heterochiral dimers found in 3 originating from various cooperative non-covalent interactions where copper anddicyanamide ions are arranged in 1D fashion (different color corresponds to different helicity).

Fig. 13. Illustration of 3D arrangement of heterochiral dimers found in 3 where copper and dicyanamide ions are arranged in helical fashion.

164 H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170

(Fig. 17) and relates to other homochiral chain of S isomers by cen-ter of inversion. Notably homochiral self-assembly may be due tothe dense packing of mononuclear copper center through theabove noted C–H� � �O interaction. Similar homochiral self-assemblyof zinc(II) coordination complexes due to dense packing in isopro-pyl alcohol and tert-butyl alcohol medium has been reported by Liet al. [26]. Notably C–H� � �p interaction (C4–H4� � �C9 = 3.675(7) Å)

between the mononuclear copper center having R and S isomersof L2 packed alternatively into 1D chain where syndiotacticarrangement of asymmetric carbon atoms occurs as illustrated inFig. 18. The concept of isotactic and syndiotactic chirality in coor-dination complexes has been established Puddephatt, Li and others[26,33]. In packing the mononuclear copper centers and perchlo-rate ions are arranged in 1D fashion and results zigzag structures

Fig. 14. ORTEP diagram (30%) and atom labeling scheme in complex 4 (all H-atomsexcept asymmetric H6 are omitted for clarity).

Fig. 15. Capped stick model representing the H-bonded heterochiral dimer found in4 (all H-atoms except asymmetric H6 are omitted for clarity).

Fig. 16. Illustration of 1D chain through C–H� � �O interaction between H–bonded heterococcur (color code same as Fig. 2).

Fig. 17. Illustration of homochiral 1D chain

H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170 165

down the c axis where hydrophilic layer are separated from thehydrophobic layer as shown in Fig. 19.

3.7. Structure of [Cu(L2)(l-1-N3)2] (5)

Complex 5 crystallized in space group P 21/c. The asymmetricunit of 5 contains binuclear copper(II) center bridged by ligand L2in meridional fashion. Similar to complex 3, in complex 5 the di-cop-per core generates from the OP bridged meridional coordinatingligand L2 upon metathesis with azide ion. It is key to note thatcomplex 1 upon anion metathesis with azide ion prefers to forml-1,1-NZ bridge di-copper core (2) rather than OP bridge but com-plex 4 upon metathesis with same azide ion generates OP bridged di-mer (5). The above observation might be due to ligand modification.In complex 5 the inversion center located directly between the twocopper ions in Cu2(OP)2 units resulting heterochiral dimerization ofligand L2 around the di-copper center. ORTEP diagram with theatom labeling scheme of the centrosymmetric dimer is displayedin Fig. 20. In 5, the coordination geometry around copper(II) centersare satisfied by two OP bridged NPNIOP-donor set of the ligand L2 andtwo l-1 coordinating azide ions oriented in trans position. Thuscoordination geometry around the five coordinated copper(II) cen-ters can be best described as distorted square pyramidal as inferredfrom the calculated s value of 0.55. The angles around the trigonalplane containing N2N3O1A atoms are 112.8(1)�, 116.7(1)�, and130.2(1)� and the trans angle is 163.3(1)�. In 5, ligand L2 bounds tothe copper center by a five-membered and a six-membered chelatering and both rings are puckered, resulting in an envelope shape forthe ligand moiety. The asymmetric carbon atom is out of plane fromthe puckered five membered rings as inferred from the dihedral an-gles of 7.81� between the plane containing C5C6N2 and C5N1Cu1N2atoms. The dihedral angle of 24.66� between the planes formed byN2Cu1O1 and O1C19C14C13N2 suggests an out of plane displace-ment of copper(II) center from envelope shaped six membered rings.The bond order around the copper center follows the trend Cu–NP >Cu–OP > Cu–NI > Cu–ND. The non-bonded OP� � �OP and Cu� � �Cudistances are of 2.663(3) and 3.153(1) Å, respectively. In complex5, distortion around the copper center makes the axial Cu–OP distanceleast in comparison to the complexes 1, 3 and 4, and consequences ashorter non-bonded OP� � �OP and Cu� � �Cu distances than others.

hiral dimers found in 4 where isotactic arrangements of asymmetric carbon centers

through C–H� � �O interaction found in 4.

Fig. 18. Illustration of 1D chain through C–H� � �p interaction between mononuclear copper centers found in 4 where syndiotactic arrangement of asymmetric carbon centersoccurs (color code same as Fig. 2).

Fig. 19. Illustration of 3D arrangements found in 4 where copper and perchlorate ions are arranged in 1D fashion.

Fig. 20. ORTEP diagram (30%) and atom labeling scheme in complex 5 (all H-atomsexcept asymmetric H6 are omitted for clarity).

166 H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170

In complex 5 cooperative C–H� � �N, localized C–H� � �p, and semi-localized C–H� � �p interactions assembles the heterochiral dimersto 3D structures. It was found that C–H� � �N interactions(C13–H13� � �N5 = 3.573(6) Å and C15–H15� � �N3 = 3.548(6) Å)between azide ion and ligand moiety assembles the heterochiraldimers to 1D structures where isotactic arrangements ofasymmetric carbon atoms occurs (Fig. 21). The noted C–H� � �N

interactions are diastereoselective in nature as it connects the Risomer of L2 in particular heterochiral dimers to S isomer of L2in nearby heterochiral dimer in � � �RS� � �RS� � �RS� � � fashion and sub-sequently consequences an inversion center in between them. Sim-ilarly a localized C–H� � �p interaction (C1–H1� � �C10 = 3.516(6) Å)and semi-localized C–H� � �p interaction (C3–H3� � �C14 (C15) =3.604(6) Å) assembles the heterochiral dimers to 2D sheet structuresas illustrated in Fig. 22. In packing the above noted cooperativenon-covalent interactions assembles the heterochiral dimers to3D structure down a axis (Fig. 23).

3.8. Effect of cooperative non-covalent interactions on the solid statediastereoselective self-assembly

Herein solid state diastereoselective self-assembly of heterochi-ral dimers on crystal engineering context are discussed. It is note-worthy to mention that during synthesis of complexes 1–5, aracemic mixture of L1H/L2H has been used and hence the isolatedfive complexes are racemic in nature each having a monochelateddimetallic core and binds to the metal center in tridentate meridi-onal fashion. The chelate ring formed by tridentate N2O donor set(NPNIOP) of racemic ligands outcomes subsequently a five-mem-bered and a six-membered ring on metalation with copper(II)ion. Overall in complexes 1–5, copper(II) center exhibits distortedsquare pyramidal geometry and anions are orientated on the axialsite perpendicular to the square plane containing the NPNIOP

Fig. 21. Illustration of 1D self-assembly of heterochiral dimers found in 5 through diastereoselective C–H� � �N interaction where isotactic arrangement of asymmetric carbonatom occurs (color code same as Fig. 2).

Fig. 22. Illustration of 2D sheet found in 5 through localized and semi-localized C–H� � �p interactions (color code same as Fig. 2).

Fig. 23. Illustration of 3D structure found in 5 through cooperative non-covalent interactions down a axis.

H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170 167

atoms. The long axial bond is due to the Jahn–Teller distortion. It isimmense important to note that all the isolated complexes have acenter of symmetry in the di-copper core and hence areheterochiral in nature. Thus in the present circumstances isolated

heterochiral self-assembly of racemic Schiff bases around the di-copper core is the preferred and stable one over the homochiralself-assembly. The aforementioned results address new examplesof rarely occurs chiral self-discriminating process. Although the

168 H.S. Jena / Inorganica Chimica Acta 410 (2014) 156–170

difference in structural arrangements can be explained mostly interms of cooperative non-covalent interactions, the role of the dif-ferent terminal anions should not be neglected. In all five com-plexes 1–5 terminal anions are orientated trans to each other andaway from the methyl/phenyl group appended to the asymmetriccarbon centers. This orientation of anions minimizes the steric con-gestion around the di-copper centers and consequence heterochi-ral dimerization of the racemic ligands. The role of counter ionsand non-covalent interactions on the solid state diastereoselectiveself-assembly are elaborately discussed.

The crystal packing pattern of complexes 1–5 are analyzed interms of C–H� � �O, C–H� � �N, localized and semi-localized C–H� � �p,non-classical C–H� � �Cl H-bonding, and parallel displaced p� � �pinteractions. It was found that in 1–5 heterochiral dimers are inter-weaved thorough above noted cooperative non-covalent interac-tions in diastereoselective manner. For example the R isomer ofligands in a particular heterochiral dimer is linked to the S isomerligands in a nearby heterochiral dimer and consequences hetero-chiral dimerization through non-covalent interactions. Althoughthere are several intelligences on the non-covalent interactions,none of them discuss about their diastereoselective nature. Sinceligand L1 in complexes 1–3 exhibits naphthalene moiety,C–H� � �p and p� � �p interactions are anticipated due to the p cloudelectrons of naphthalene ring. In 2, a localized C–H� � �p interactionassembles the heterochiral dimers to 2D structure. Similarly theuncoordinated N atom of the azide ion involves in C–H� � �N interac-tion with the ligand moiety to consequence 2D sheet structureswhere ligands are arranged in helical fashion. In 3, the presenceof parallel displaced p� � �p interaction between naphthalene–naph-thalene face to face heterochiral dimer and benzene–naphthalenedimer accumulates the heterochiral dimers into 1D structure. Sim-ilar to complex 2, in 3 terminal uncoordinated N atom of dicyan-amide ion involves in C–H� � �N interaction with the ligand moietyand assembles the heterochiral dimers to form 2D structures. Itwas found that the aforementioned C–H� � �p interaction in 2 andC–H� � �N interaction in 3 results supramolecular MOF structure. Itis worthy to note that the aforesaid C–H� � �p and p� � �p interactionsfound in 2 and 3 are absent in 1 which yields the substantial effectof anion metathesis on the solid state supramolecular self-assem-bly. The helical arrangement of the ligand moiety in 1–3 enhancesthe role of ligand modification on the final arrangements as earliersuch rearrangements are not found in salicylic derivatives of race-mic Schiff bases. In order to understand the effect of ligand modi-fication, salicylic derived ligand (L2) is used in synthesizingcomplex 4 and 5. In 4 the coordinated water molecules involvedin diastereoselective H-bonding interactions with perchlorate ionand OP atoms simultaneously to result heterochiral dimer. Thenoted H-bonded heterochiral dimer extends through differentC–H� � �O and C–H� � �p interactions to 3D zigzag structures wherethe hydrophilic regions are quite separated from the hydrophobicregions. In 5, upon anion metathesis the axial coordinated azideion exhibits C–H� � �N interactions with ligand moiety to accumu-late the heterochiral dimers into 1D self-assembly. A notablyC–H� � �p interaction extends the 1D assembly to 2D sheet struc-tures. It can be anticipated that the present discussion will boostthe preliminary knowledge for the possible self-assembly of race-mic Schiff bases on complexion with suitable metal ions and alsoto explore the role of anions and non-covalent interactions onthe coordination networks or coordination framework in future.

4. Conclusion

To explore the significant effect of non-covalent interactionsand co-ligands on the solid state diastereoselective self-assemblyof coordination complex containing racemic Schiff bases, five

copper(II) heterochiral complexes are synthesized and structurallycharacterized. Determination of molecular structures of 1–5 con-firmed the presence of centrosymmetric dimer having Cu2O2 andCu2(NZ)2 core where ligand exhibits both R and S configurationswhich results heterochiral dimerization of ligands around cop-per(II) center in chiral self-discriminating manner. It was foundthat in 1–5 heterochiral dimers are interweaved thorough cooper-ative non-covalent interactions in diastereoselective manner. Incomplex 2, azide ion shows l-1,1-bridging mode whereas in 5 itshows terminal bridging mode. In complex 3, dicyanamide ionshows terminal bridging mode. In complex 1–3, the presence ofnaphthalene moiety in ligand backbone engenders various p� � �pand C–H� � �p interactions between heterochiral dimers which con-sequences supramolecular helical arrangements. In 4, diastereose-lective H-bonded heterochiral dimers are extended throughC–H� � �O and C–H� � �p interactions to 3D zigzag structures wherethe hydrophilic regions are quite separated from the hydrophobicregions. In 5, notably C–H� � �N interactions between azide ion andligand moieties self assembles the heterochiral dimers to networkstructure. The isotactic and syndiotactic arrangements of the coor-dination complex through non-covalent interactions are substan-tially studied. The aforementioned results demonstrate thatligand modification, anions and non-covalent interactions playsdomino role on controlling the solid state structural rearrange-ments of the complexes. Further studies on diastereoselectiveself-assembly of coordination complex containing newly designedracemic Schiff bases are in progress.

Acknowledgment

We are grateful to the Department of Science and Technology(DST), New Delhi, for establishing single crystal X-ray diffractome-ter facility under FIST scheme and IIT Guwahati infrastructuralsupport. HSJ thanks Dr. Sanjit Konar and Indian Institute of ScienceEducation and Research Bhopal for a post-doctoral fellowship.

Appendix A. Supplementary material

CCDC 957070–957074 contain the supplementary crystallo-graphic data for 1–5. These data can be obtained free of chargefrom The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated withthis article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2013.10.035.

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