I ndian Journal of Chemistry Vol. 42A. September 2003. pp. 2307-2315

Effect of supramolecular aggregation on coordination in cobalt (II) complexes of 2-imidazolidone

Larry R Falvello*, Eva M Miqueleiz & Milagros Tomas

Depart ment of Inorganic Chemistry, University of Zaragoza, Plaza San Francisco sin. E-50009 Zaragoza. Spain

Received 30 December 2002

The polyfunctional ligand 2-imidazolidone, HimiO, CJ H6N20, reacts rapidly with cobalt chloride hexahydra te at ambi ent temperature to produce the deep blue product [Co(HimiO)6][CoCI4], 2, which can be kept in solutio n or isolated as stabk crystals. A solution of 2 reacts under slightly more forc ing conditions with replacement of two HillliO li gands of the ca ti on by water to g ive the pale pink compound [Co(HimiOM H20hlC I2'2 HimiO, 3, which is isola ted onl y in crysta lline forill . Upon dissolution in acetone, compound 3 reverts to 2. Crystals of 3 display full use of the hydrogen bonding capabilities of the functional groups, both donors and acceptors, and are comprised of unbounded columnar aggregates held together into bundles by hydrogen bonding with interstitial, unligated HimiO molecu les. The aqua ligand plays a key hydrogen-bonding ro le in the formation of both the columns and the bundles. It is concluded that compou nd 2 is the favored product in solution and that the formation of stab le aggregates dri ves the crystalli zat ion of 3, which is favored in the solid state.

Introduction

The coordination chemistry of first-row transItIon e lements with polyfunctional ligands has demonstrated to-date that the solid products isolated from even relatively simple reaction systems depend to an important extent o n the nature of the non­covalent interactions that are fo rmed during crysta lli zat ion or, less probably, carried into the crystal fro m solution. In studies of complexes with cyan urate, 1.2 for example, we have observed that the coordi nation number alld geometry can be adj usted to the requirements of a specific supramolecuJar aggregate, and that the aggregate is the entity that persists across a series of crystalline solids in which metal, aux il iary ligand, coordi nation number and coordination geometry vary widely. The same hydrogen-bonded aggregate of cyan urate persists through - and perhaps drives - a second-order phase transformation in crystals of a nickel complex, in whi ch the shape of the molecular complex can be va ri ed reversibly with temperature while the shape of the supramolecular structure remains unchanged. ) Saccharinate, used as a polyfunctional ligand, has been shown to adopt four different coordination modes in the products of one reaction system, in which the presence or absence of supramolecular structures plays an important role in determining which coordination modes are observed in the molecular solids.4 In complexes with cyanide, we

have observed that the isolati on of discrete molecular products as opposed to polymers, as well as the shapc of discrete molecules in the solid state, depend importantly on the presence or absence of hydrogen bonding.5•

7

2-imidazolidone , 1

The cyclic organic compound 2-imidazolidonc. 1 (HimiO, also imidazolidinone or ethy leneurea ), is a urea derivative that has several tech nologicully important applications and is 1I eful in o rga ni c- and biochemistry. A family of herbi cides is derived from HillliO,8 and this compound or organic compouncl~ that contain an HimiO fragment are useful in the synthesis of amino acids and antibioti cs.') Some re lated compounds have antimicrobial activity. III In addition, rhodium cata lysts with 2- imidazolidonc among other species have shown catalytic activity in the synthesis of lactones and lactams . i I

Our interest in HillliO stems from its possibilities for use as a po!yfllnctional ligand in coordination chemistry. The five-membered ring possesses three functiona l groups, a carbony l and two umides. The latter can act as single hydrogen-bond donors. whi Ie

2308 INOlAN J CHEM. SEC. A. SEPTEMBER 2003

the fo nner is a pote ntial double hydrogen bond acceptor. The ethylene moiety that completes the ring presents the capability of forming van der Waals' interactions w ith its surroundings in the crystalline state. and so marks the principal difference between ths li gand and a ligand such as the five-membered r ng compound parabanic acid or the six-membered t yanurale , which have functional groups capablc of j )rming hydrogen bonds at all ring positions.

Some coordination chemistry with HiflliO has been d . I C I . h 12 . 13 repol1e prev IOUS y. omp exes Wit mercury, till,

copper,14 and cadmium 15 are known, but we are not

aware of any previously reported complexes of HillliO wi th cobal t. We report here the preparation, characteri zation, and structures of two solid state systems contall1l11g Co HillliO complexes [Co(HimiO)6] [CoCI4], 2 and [Co(HimiO)4 (H20 h) C I2·2 HimiO, 3.

Materials and Methods All so lvents and reagents were purchased from

commercial vendors and used as received. Infrared spectra from 4000 to 200 cm' l were obtained from

ujol mu ll s between polyethy lene sheets, using a Perkin-Elmer 883 spectrophotometer. E lemental analyses were performed using a Perkin-Elmer 2400 microana lyzer.

SVlllhesis of[Co(HillliO)r,)[CoCi-/}, 2 To a solution of 0.100 g (0.420 mmol) of cobalt

ch loride hexahydrate in acetone (30 mL) was added 0.217 g (2.52 mmol) of 2-imidazol idone. T he mixture was st irred for five minutes, giv ing a light blue solid and an intense blue solution . The solid was fi ltered off on a fritted glass plate and dried with several fractio ns of II -hexane; yie ld, 75%. Anal. Found: C, 27.82; H, 3.97 : N, 21.60: Calcd. for C ISH36C02CI4N 120 6: C, 27.85: H, 4.67; N, 21.65%. IR v(N-H) 3319, v(C=O)

1659, vb(N-H) 1512, v (M-Cl) 3 12, 290 cm' l. Crystals of 2 for X-ray structure determinatio n

were obta ined by liquid diffusion. A layer of It-hexane was carefully deposited over 2 mL of a solution prepared fro m 3 mg of compound 2 and 5 mL of acetone, in a 7 mL test tube. Slow diffusion of the two layers at room temperature yielded blue crystals of lCo( HimiO)6][CoCI4] within a period of several days,

SVlllhesis of [Co(H inziOM H20 h lCl2'2(HimiO), 3 T he first part of thi s preparation is identical to the

preparati on of 2 described in the previous paragraph. To a solutio n of 0.100 g (0.420 mmol) of cobalt

chloride hexahydrate in acetone (30 mL) was added 0.217 g (2.52 mmol) of 2-imidazolidone. Aftcr ri \"(' minutes of stirring, the mixture consisted of a dee p blue supernatant over a light blue precipitate. At this point, the volume of the solution was reduced under vacuum (without prior fi ltering) to about 15 mL. after which the mixture was stirred for about 30 min. Th ere remained a li ght blue solution over a pink precipitate. The latter was filtered on a glass frit and dri ed with several aliquots of Iz-hexane; yield, 96%. Anal. Found: C, 31.68; H, 5.77; N, 24.66; Calcd. ror CI SH40NI 20 SCoCh: C, 31.68; H, 5 .91; N, 24.63*. IR v(O-H)/(N-H) 3376, 3195, v(C=O) 1660, Vh( - /-I )

1510cnfl.

Crystals of compound 3 for X-ray s tructur~

determination were obtained from the blue supernatant solut ion that remained from the preparation of compound 2, after the crysta ls of 2 had been removed. The solution was allowed to stand at _5° C. for severa l days, at which time pink crystal s of 3 with quality sufficient for structure determination were harvested ,

Data collectionJor X-ray crystallography For each complex, 2 and 3, s ing le-crystal

diffraction data were measured on an auto mat ed CAD-4 di ffrac tometer l 6 using graphite­

monochromated MoKa radiation (A. = 0.7 1073 A). The crystals were fixed to the ends of g lass fibers wi th epoxy. In each case, accurate un it cell parameters were determined by a symmetry constrained least-squares fit to the positions of 25 reflections, each centered at four d iffere nt goniometer setti ngs so as to minimize the .effects of instrument calibration errors. For intensity data collect ion. th e

scan method (w-scans for 2, w-28 scans for 3 ) was

chosen on the basis of two-dimensional (w-8) sca ns 01" a number of well-cente red re flections. Data reduct ion included the application of Lorentz and polarization

. 17 II b' . 18 B I correctIOns, as we as a sorptIOn corrections. o r 1

structures were solved by direct methods, I') and the least-squares refi nements and Fou rier calculations were done with the program SHELXL-97 ?O

X-ray crystal structure determinatioll or [Co(HimiOM[CoCI41,2

Crystal structure formula C ,sH36C02Cl4N 120 (" M = 776.24, monoclinic space group P2/c (no. 14). (f = 9.3665(4) A, b = 19.2345(12) A, c = 18.0249(11) A. [a = y = 90°], f3 = 98.629(6t, V = 3210.6(3) }...-1. T =

FALVELLO et al. : STUDY OF Co (II) COMPLEXES OF 2-IMIDAZOLIDON E 2309

297-298 ± 1 K, Z = 4, J..l = 1.42 mm-I; 7339 unique and 3889 observed reflections out of 7803 measured with 2.0 < e < 27.47°, R(int) = 0.0338, number of variable parameters 380. Refinement method: full ­matrix least-squares on r , final residuals [J > 2a(1)): R 1 (obs) 0.0610, wR2 = 0.1291; (all unique data): RJ = 0.1329 , wR2 = 0.1487.

X-ray crystal structure determination of {Co(HimiOMH20h)Cl2'2(HimiO),3

Crystal structure formula CISl40NI20gCoCIz, M = 682.43, monoclinic space group P2l/c (no. 14), a = 8.7341(5) A, b = 10.0762(5) A, c = 16.8446(12) A, [a= y = 90°], ~ = 96.356(5t, V = 1473.3(2) A3, T = 297-298 ± I K, Z = 2, J..l = 0.827 mm-I; 2581 unique and 1964 observed reflections out of 2764 measured with 2.0 < e < 25.0°, R(int) = 0.0289, number of vari able parameters 267. Refinement method: full­matrix least-squares on r, final residuals [J > 2a( I)): R/(obs) 0.0407, wR2 = 0.0905; (all unique data) : Rl = 0.0666 , wR2 = 0.1031.

Strllcture analysis and refinement

For [Co(HimiO)6][CoCI4 ] , 2, the initial solution of the structure by direct methods yielded most of the non-hydrogen atoms. This was followed by the usual iterati ve sequence of least-squares refinements and di ffe rence Fourier maps, which revealed the remaining non-hydrogen atoms . While most of the hydrogen atoms were visible on difference maps, for the fin al refinement, all the hydrogens were placed at calculated positions and refined as riding atoms with isotropic displacement parameters set to 1.2 times the isotropic or equivalent isotropic displacement parameters of their parent carbon or nitrogen atoms. (The two hydrogen atoms attached to C( 13) were omitted because the calculation of their positions was rendered dubious as a result of disorder of the neighboring atoms.) Of the six HimiO ligands present in the asymmetric unit, two were found to be di sordered over two positions each (vide infra). For each of these two moieties, the relative occupancy of the disordered congeners was treated as a variable parameter in the least-squares refinement. Furthermore, the non-hydrogen atoms involved in the di sorder were refined isotropically. All remaining non-hydrogen atoms were refined independently with ani sotropic displacement parameters. In all, the fin al stable, convergent least-squares cycle fitted 380 parameters to 7339 data, for a data-to-parameter ratio

of 19.3. The largest positive and negative dille rencl' densities at the end of refinement were +0 .50 and

o 3 -0.37 elA .

For [Co(HimiOMH20 h ]CI2'2(HimiO), 3. the direct-methods calcul ation yielded the positio ns of all of the non-hydrogen atoms. All hydrogen atoms were located in difference Fourier maps and included in the structural model as independent atoms with isotropic displacement parameters. All non-hydrogen atoms were refined anisotropicaliy . In all , 267 vari able parameters were fitted to all 258 1 unique data. for a data-to-parameter ratio of 9.7. At the end 0 1" refinement, a final difference Fourier map had larges t positive and negative peaks of +0.27 and - 0 .38 e/k 1

.

Results and Discussion Compounds 2 and 3 are stable pm ducts that emerge

serially from the same reacti on sys tem. The I"irs! product, 2, is formed almost immedi ately and can be isolated and stored indefinite ly. Neverthe less, with only slightly longer reaction times and s lightl y more forcing conditions, product 3 is formed almm ! quantitatively . This sort of behavior. whi ch is to be expected when an intermediate is re lat ive ly unstabl e. is not predicted when the first product iso lated is quit e stable. By way of explaining the behav ior of these ~ ­

imidazolidone complexes of cobalt, and especi all y the facile evolution of 2 to 3, we shall examine the crystal structures, and particularly the interacti ons In intermolecular space, in detail.

Synthesis and characterization of (Co(HillliO )(,/ [CoCI4). 2

Cobalt forms complexes with a ri ch vari ety 0 1" coordination geometries - s ix-coordinate oc tahecl ral. four-coordinate tetrahedral and squ are-planar. and five-coordinate arrangements have all been observed in discrete molecular complexes. In [Co(HimiO ),, 1 [CoCI4], 2, a dieationie, homolepti c octahedral Co(l l) complex is present alongside a dianionic, homolepti c four-coordinate tetrahedral co mplex of Co(ll ). Th is product is the first one formed when cobalt dichlo ri de hexahydrate is reacted with 2-imidazolidone in rati o~

of from 1:3 to 1 :9.

The IR spectrum of 2 shows the charac teri:-- tic bands for the amide and carbonyl function s at 3319 and 1659 cm-I, respectively. In the Co-Cl region, two bands appear at 328 and 305 cm-I, indicating th at the anion or its environment dev iate fro m perfec t T" symmetry.

23 10 INDIAN J CHEM, SEC. A, SEPTEMBER 2003

Complex 2 crystallizes in the monoclin ic system, space group P2 tic. with a formal composition of one formu la per crysta llographic asym metric unit. However, the asymmetric unit compri ses two crysta ll ographically independent half-cations with their cobalt atoms on centers of symmetry , along with c ne [CoC14f an ion on a general position. Each cation (Onsists of the cobalt cen ter surrounded by six neutral

Fig. I-Thermal ellipsoid plot of cation J of (Co(Hi miO)6]2+ from the crystal structure of [Co(HimiO)6][CoCI4], 2, showing the alOm labelling scheme. Non-hydrogen atoms are represented by their 50% probability ellipsoids.

Fig. 2-Thermal ellipsoid plot of cation 2 of [Co(HimiO)6f+ from the crystal structure of [Co(HimiO)6][CoCI4], 2. showing the atom labelling scheme. Non-hydrogen atoms are represented by their 50% probability ellipsoids.

HimiO ligands, three of them crystallographicall y independent, and all bound to Co through the carbonyl oxygen atom of the ligand. Table I give~ ~t

li st of significant bond distances and angles ill the structure of 2. Figure I is a drawing of the cat ion centered on Co(2), and Fig. 2 shows the cat ion centered on Co(3). As can be apprec iated from the figures, one of the independent HillliO ligands i ~

di sordered in each case; as it turns out, the disorder has a clear explanation .

With reference to the cation centered on atom Co(2), we observe that there are three somewhat different Co-O bond distances, but that the mmt noticeable difference is between the longest of these and the other two (Table 1). The oxygen atom involved in the longest contact to the meta l, Co(2 )-0(11), 2.136(3) A, acts as the receptor for two hydrogen bonds in which the donor atoms are N-H amide functions of two other li gands. Table 2 gives

Table I - Selected bond lengths (A) and angles (0) for [Co(HimiO)6](CoCI4], 2

Co( I )-CI(3) Co( I )-CI(4) Co( J )-CI(2) Co( I )-CI( I) Co(2)-O( I ) Co(2)-0(6) Co(2)-O(l I ) O( I )-C( I ) 0(6)-C(6) O(II)-C(II) 0(16)-C(16) Co(3)-0(16) Co(3 )-0(26) Co(3 )-0(2 1) 0(2 J )-C(2 1 ) 0(26)-C(26) CI(3)-Co( I )-CI( 4) CI(3)-Co( I )-CI(2) CI( 4 )-Co( 1 )-CI(2) CI(3 )-Co( I )-CI( I ) CI( 4 )-Co( J )-CI( I ) CI(2)-Co( I )-CI( I ) O( I )-Co(2)-0(6) 0(1 )-Co(2 )-0(11 ) O( 6 )-Co(2 )-0(11 ) C( 1 )-O( J )-Co(2) C(6)-0(6)-Co(2) C( J I )-O( I I )-Co(2) C( 16)-0( 16)-Co(3) O( 16)-Co(3)-0(26) O( I 6)-Co(3)-0(2 I ) 0(26)-Co(3)-0(21 ) C(21 )-0 (21 )-Co(3) C(26)-0(26)-Co(3)

2.2443( 16) 2.2760( 17) 2.28 12( 16) 2.2927( 16)

2.058(4 ) 2.081(4 ) 2. 136(3) 1.250(6) 1.23<)(6) 1.248( 5 ) 1.24H(6) 2.065( 3) 2.098(3 ) 2. 105(3) 1.247(5) 1.252(6)

109.74(8) 105.69(6) 110.54(7) 108.72(7) 108.90(7) 11 3. 18(6) 92.77( 17) 92.61( 14) 86.64( 14)

134.1(3) 132.7(4) 125.5(3) 133.5(3 )

89.34( 14) 92.97( 13) <)0.22( 13)

129.9(3) 128.7(3)

FAL VELLO el al. : STUDY OF Co (II) COMPLEXES OF 2-IMIDAZOLIDONE 2~ II

Table 2 - Principal non-cova lent interactions in the crystal structure of lCo( HimiO)611CoC I~] . 2 ( D = Donor. A = Acceptor. distances in A. . angles in degrees)

D-H.A d(D-H ) d(H ... A) d(D ... A) « DHA)

N( 12A)-H( 12A).0 (6) 0.86 2.11 2.803( II ) 137. 1

N(2)-H(2).C1(2)#3 0.86 2.51 3.335(5) 161.3 N(5)-H(5).0 ( II ) 0.86 2.23 2.954(6) 141.3 N( 12B)- H( 12B).0 ( 1)# I 0.86 2.06 2.758( 10) 138.3 N(7)-H(7) .0 ( 11 )# I 0.86 2. 19 2.9 18(6) 142.8 N( 17)-H( 17).0 (2 1) 0.86 2.32 2.930(5) 128.6 N(20)-H(20).CI(4) 0.86 2.5 1 3.344(5) 163.6 N(30)- H(30).0(2 1 )#2 0.86 2.25 2.952(6) 138.4 N(25A)-H(25A).C1 ( I )#4 0.86 2.87 3.386(7) 120.1 N(25B)-H(25B).CI( I )#4 0.86 2.49 3.25 1( 12) 148.2 N(22)-H(22).0 (26) 0.86 2. 17 2.841(6) 134.5 C(3)-H(31 ).CI( 1)#3 0.97 2.79 3.636(6) 146.4 C(9)-H(92) .CI(3)#5 0.97 2.68 3.540(6) 148.4 C(23 )- H(232).CI(2)#6 0.97 2.88 3.635(7) 135.3 N( 15A)-H( 15A).CI(4) 0.86 2.84 3.516( 12) 136.9 N( 15 B)-H( 15B).CI(4) 0.86 2.73 3.433(11) 140.5 C( 14B)-H( 14D).CI(3)#7 0.97 2.77 3.527( 15) 135.7

Symmetry transformations used to generate equivalent atoms: # 1 -x+l.-y+I ,-z+1 #2 -x+ I ,-y+ l.-z #3 x,-y+3/2,z+ 1/2 #4 -x,-y+l.-z #5 -x.-y+ l.-z+1 #6 x.-y+3/2.z-1/2 #7 -x.y- I 12.-z+ 1/2

the principal non-covalent interactions in the structure of 2. Atom O( 11) is the only one of the three independent ligand oxygen atoms th at is involved in two hydrogen bonds, and the existence of these interactions is the most probable explanation of the longer Co-O contact.

Also with re fe rence to the cation centered on Co(2), in Fig.1 it can be seen that the same li gand suffers a static di sorder of its ring over two di stinct orientations. While the steric implications of one or the other of the disordered orientations do not seem to be important, it turns out that the two orientations gi ve rise to di stinct but energetically similar intramolecular hydrogen bonds. In one orientation, atom N( 12) of the ring points to carbonyl oxygen atom 0 (6) of a neighboring ligand, forming a moderately strong hydrogen bond [ (12A) .. . 0(6) = 2.803(11) A]; and in the OIientation of the second congener, atom N(l2) points to oxygen O( I ') of the other neighboring HimiO ligand, forming an equally strong hydrogen bond [N( 12B) ... 0(l ') = 2.758( I 0) A]. This ligand is not involved in significant intermolecular hydrogen bonds (Table 2), so with both orientations giving rise to similar intramolecular interactions it is not surprising that the relati ve occupancy parameter for the two congeners was refined to a value of 0.504(11) - that is, 50% occupancy for each olientatioll. The disorder is such that three atomic sites of this ligand - namely C and 0

of the carbonyl moiety and ethylenic carbon alom C(l3) - are shared by both congeners. while the tW(l nitrogen atoms and the remaining carbon atom are disordered over two positions (Fig. I ).

The second cation also sits on a crystall ographic center of inversion, with three independen t Co-O distances. Again. one of the li gands suffers disordcr. but in thi s case only one of the non-hydrogen atomic sites of the ring, N(25) , was clearly split over t\\'o congeners. Except fo r the carbonyl moiety , the olher atoms of thi s ligand showed the effects of disorder in the form of transversally elongated di splacemen t ellipsoids, as shown in Fig.2.

The intramolecular hydrogen bondin g is not affected by the disorder in the second cation. One of the oxygen atoms, 0 (21), accepts two hydrogen bond~

from amide groups of neighboring li gands (Tab le 2). while 0 (26) of a second ligand accepts one hydrogcn bond. The carbonyl oxygen of the third li gand d()c~

not participate in non-covalent interacti ons. The di sorder of atom N(25) affects only the intermolecular interactions, with this atom donating to a chl orine atom of the anion either in a hydrogen bondIN (25B)­CI(l'), 3.251(12) A] in one congener or in a weaker contact [N(25A) ... CI( I '), 3.386(7) A] in the other. The latter lies outside the sum of the van der Waal s' radii of the two atoms involved,~' but it likely still serves as a stabi li zing innuence on the structure. The

2312 INDI AN J CHEM, SEC. A, SEPTEMBER 2003

difference in the strengths of these two interactions is not reflected in the re lati ve populations of the two di sordered congeners; N(25B), which forms the stronger interaction, has a refined population parameter of 41.4( 17)%.

Finally, we note that the formation of the Co-O bonds and the hydrogen bonds to the ligated oxygen atoms does not appear to affect the carbonyl C=O bond significantly. The C=O bond distances (Table 1) are sim il ar to that found in the crystal structure of the free ligand in the hemihydrate [1.262(4) A]22 and do not vary widely with in this structure. Also, the carbony l band in the IR spectrum of 2 appears at 1659 cm· l

, an energy quite similar to that observed for the free li gand , 1656 cm· l

.

SVllthesis alld characterization of Cor HimiO)4 (H]OhlCl2'2(Hil71iO),3

The reac tion that produces [Co(HimiO)6][CoCI4],

2. can be taken further under slightly more fo rcing cond itions - concentration followed by sti rri ng - to g ive the pale pink product [Co(HimiO)4 (H20 h JCh'2 (HimiO), 3. Since the first product, 2, is already quite stable. the fact that further reaction occurs without the addition of any other reagent poses interesting questions regarding the nature of the final product and the driv ing force for the reaction. When the pink product 3 is di ssolved in acetone, the resulting solution has the deep blue colour of the first product -th at is. the characteristic colour of the tetrahedral anion lCocl4f. The o nly method that we have fo und for restoring crystalline 3 from this sol ution is to repeat the procedure that produced 3 in the first place, namely, concentration and stirring w ith possible variations such as cooling of the resulting solution. But dissol ving and recrystallizing 3 in the usual fashion does not succeed in restoring the pink crystalline product directly. Rather, d issolut ion of 3 produces 2 - a process invo lving both dissociation and fo rmation of Co-HimiO bonds. From this process, complex 2 can be precipitated in yields which vary with conditions of temperature and concentration , as in the initial synthesis.

The conversion of the initial product, 2, with a Co:HimiO ratio of I :3, to the second product 3 (Co: HimiO ratio I :6) proceeds with as high a y ie ld as the availabi lity of HimiO permits. When the preparation is done as described earlier, with a Co:HimiO ratio of I : 6, the yield of isolated product is almost quantitative (96%). Qualitatively, we have observed that the two-step reaction proceeds to the

Fig. 3-Thermal ellipsoid plol of the cation frolll th e: cry,lal structure of [Co(HillliOMH 20hJCI 2·2(H illl iO). 3. showing IhL' atom labelling scheme. Non-hydrogen atom, are represented Iw their 50% probability ellipsoids. .

same products when Co:H imiO ratios of from 1:3 to I :9 are used.

As is the case with many sys tems containin& polyfunctiona l li gands, the key to understanding thi s two-part reaction lies in the crystal s tructure formed by the final product. In this case, all of the potential hydrogen-bond donors and acceptors on the chemical entities present participate in forming a stab le supramolecu lar aggregate.

The comp lex dication in 3 was found to be [Co(HimiOM HzOhf+, an octahedral co mplex which resides on a crystallographic inversion center. The two aq ua ligands a re tralls- to each o ther, as shown in Fig. 3, and are slight ly c loser to the cobalt center than are the four HillliO ligands in the equatoria l plane (Table 3). Because of the inversion ce nter, only three of the Co-O bonds are independent. In addition to thi s half-complex, the crystallographic asymmetric unit formally contains one ch loride anion and one unligated molecule of Hill1iO, thus giv ing the overall stoichiometry of [Co( HimiOMHzO)2lClz·2( HimiO ).

An important feature of the crystal struc ture of :3 is the presence of a very complete networ ' of hydrogen bonds, as summarized in Table 4 . Every possib le hydrogen bond donor and acceptor is used in this pattern. Considering fi rst the complex cation. there are four intramolecular hydrogen bonds that unite the ligands around the equatorial plane. These are not strong interactions [N(2) ... 0(6) , 2.904(4) A:

FALVELLO el 01. : STUDY OF Co (II ) COMPLEXES OF 2-IMIDAZOLIDONE

N(7 ) ... O(l '), 2.997(4) A], but they serve to stabilize the structure . The functional groups of the ligated HillliO moieties are further invo lved in intermolecular interactions; N(5) donates a hydrogen bond to the carbo nyl oxygen of the unligated HimiO, and N(lO) do nates to the chloride. At the same time, carbonyl oxygen atom O( \ ) receives a hydrogen bond from the amide group at N( 17) o f the unligated imidazolidone, thi s second H-bond being consistent with the fact that the Co( I )-O( I ) bond is the longest of the three independent metal-ligand contacts. One of the ethylenic carbon ato ms o f HimiO, C(9), is involved in a non-bonded interactio n with the chloride, as seen in Table 4.

The stronges t hydrogen bonds in the structure are those do nated by the aqua li gand. One of these has chloride as receptor, and the short di stance is accompanied by an almost linear di spositi on [O(l I) ... Cl ' = 3.073(3) A, O ( ll )- HC1\\ ) .. . CI' = I 74(4t] . The sum of the van der Waals' radii o f 0 and CI can be estimated as 3 .27 A,2 t so this is seen to be a quite favorable interactio n. The second H-bond th at is donated by the li gated water has 0(16) of the free HillliO as recepto r. This is a moderately strong

Table 3 - Selected bond lengths (A) and angles (0) for [Co( HimiOl4(H20hlC I2'2( Himi O), 3

Co( I)-O( II) Co( I)-0(6) Co( I)-O( I) O( I)-C( I ) 0(6)-C(6) O( 16)-C( 16) O( II )-Co( I )-0(6) O( I I )-Co( I )-O( I ) 0(6)-Co( I )-O( I ) C( I )-O( I )-Co( I ) C(6)-0(6)-Co( I )

2.067(3) 2.092(2) 2.115(2) 1.257(3) 1.246(4) 1.246(4)

90 .48( 1 0) 9 1.83( 10)

92. 10(9) 133.9(2) 132.3(2)

hydrogen bo nd, with 0(11 ) ... 0 ( 16') = 2. 777(4) A and 0 ( 11 )-H(l12) ... O(l 6') = 178(4t.

All o f the hydrogen-bo nding functi o ns of the unli gated molecule o f 2-imidazolido ne are used: the amide nitrogen ato ms do nate H-bo nds to O( I). as mentioned above, and to the chlo ride. whil e the carbo nyl oxygen serves as accepto r in two hydrogen bonding interactio ns as me ntioned above - o ne frolll an amide of li gated Hil'lliO and o ne fro m the aqua ligand. In a similar fashi on, the chloride ani o n acts as receptor in four e lec trostatic co ntacts, at least three of which are c learly stabilizing.

Thi s set o f non-coval ent inte rac ti ons unites the varied and seeming ly di sparate e lements of the structure into a hi ghly o rdered pattern of regular forms. Firstl y, the cationic [Co(HimiOL( H20 ):,f+ and anio nic chloride fo rm an unbounded o ne-dimensional column ar chain medi ated by hydrogen bonding inte racti ons. These chains, shown in Fig. 4 , are electrically neutra l and are propagated in a direction paralle l to the crysta llographic a-ax is. Furthermore. these chain s, whi ch we describe as colu mnar inasmuch as they are not fl at, run parall e l to each other fo rming bundles he ld together by the free molecules of 2- imidazolido ne. As noted already, all of the H-bonding functi ons o f the unligated HillliO parti c ipate in favo rable interac tio ns: half of the interactio ns in volving a given free HilliiO moiety re late it to one neighboring [Co(HimiO).j( H20UCI 2

chain and the other half to another. So while the chlo ride anions may be co nsidered to be the g lue that unites the complex cations into in finite chain s, ,",ve see that the neutral 2-imidazolidone serves to fi II the space between chains whil e ho lding them together strong ly in bundl es. Each catio n-anio n pair in a chain makes hydrogen bonds to fo ur surround ing 2-

T able 4-Princ ipal no n-covalent interactions in the crystal structure of [Co(H i m iO).j( H 20hlC I ~·2( HimiO). 3 (0 = Donor, A = Acceptor, di stances in A, angles in degrees)

O- H ... A N(2)- H(2) .. . 0(6) N(7)- H(7) ... 0( 1) # 1 O( II )- H(I II ) ... CI #2 0( 1 I)- H( t 12) ... 0( 16) #2 N(5)- H(5 ) ... 0( 16) #3 N( I OJ- He 10) .. . CI N(20)- H(20) .. . CI #4 N( 17)-H( 17) ... 0( 1) #5 C(9)- H(92) .. CI #6

d(D-H) 0.76(3) 0.8 1 (4) 0.89(4) 0.77(4) 0.80(3) 0 .87(4) 0.84(5) 0 .73(3) 0.95(5)

d(H ... A) 2.23(3) 2.39(4) 2. 19(4) 2.00(4) 2.1 7(4) 2 .34(4) 2.46(5) 2.23(3) . 2.65(6)

Sy mmetry transformat ions used to generate equi valent atoms: # 1 -X .-y,-Z #2 -x+ I,-y,-z #3 -x+I ,y- 1I2,-z- 1/2 #4 x.-y+ 1/2.z- 1/2 #5 x+ 1,y,z #6 -x +I ,-y+I ,-z

d(D .. . A) 2.904(4) 2 .997(4) 3.073(3) 2.777(4) 2.937(4) 3.205(3) 3.250(4) 2.958(4) 3.598(5)

« OH A) 149(3) 132(-1) 174(4) 178(4) 159(3) 176(3) 157(5) 173( 4) 174(4)

23 14 I DIAN J C HEM . SEC. A. SEPT EMB ER 2003

Fig. 4 - Co l1llllnar chains fo rmed by the cations and chl o ride ,!Ilion, in crysta ls of [Co( HimiO)4( H20hlCI 2·2(HimiO). 3.

Fig. 5 - View of the c rysta l struc ture of [Co( Himi O)4-(H20 h lC I}'2( Himi O), 3 , down the c rysta llographic a -ax is, showing the late ra l inte rac ti ons in volvi ng lInli gated Hill1iO. O( 16A) and its re lati ves a re carbonyl oxygens o f these mo ie ties.

im idazolidone moieti es, which In turn form in teracti ons with as many neighboring chains. Figure S gives a view of the extended structure down the crystall ographic a-axis, showi ng some of the interac ti ons involving the interstitial Himio.

The two strongest hydrogen bonds in the structure are those that are donated by the aqua li gand. One of these has chloride as acceptor. and thus plays a pi votal role in the supramolecul ar chain struc ture that is propagated along the a-ax is. The second of' Ih ese hydrogen bonds has the carbonyl oxygen atom of the unligated HimiO as receptor, and thus is one of tht' key elemen ts uniting the chains into bundles and co mpleting the three-dimensi onal supramolec ul ar aggregation. The aqua ligand, then. is the keystone in the fo rmation of the supramolecu lar structure. fo rming strong interac tions both withi nand betwccn the chains which are the principal features or th is product in the solid state. We may look to the hydrogen bonds involving the water ligand for an ex planati on of the fac t that in 3, unl ike in 2. two of the HillliO moieti es are not bound to the coba lt cent er. but rather are replaced by wate r.

Conclusion We conclude from the fo regoing that co mpound 2.

[Co(H imiO)6][CoCI4 ] , is the favored prod uct in so lution upon the reacti on of coba lt dich loride hexahydrate with 2- imidazolidone , and that compound 3, [Co(HimiOM H20 h]Cl2·2(HimiO). is the favored product in the crystalline state. In crys tals of 3 all of the possible hydrogen bond donors and acceptors are used, whi ch confe rs add iti onal stabili ty to the solid. Crystals of 2 are qu ite stab le. bu t with the displacement of two HillliO li gands ill favo r of water. a si mple so lid state packing arrangement based on regul arly shaped supramolecular aggregates can be formed. The additional stability confe rred on the fi nal produc t by intermolecular interacti ons is suffi cien t to dri ve the system towards the iso lati on of wh at is the less favored product in solution. Th is reac tion system and the two products isolated in sequence demonstra te the importance and potenti al of the in teracti ons ac ross intermolecul ar space in the obtention and understanding of products which may not be eas il y sustainable in solution.

Acknowledgment We thank the Spani sh Ministry of Science and

Technology for fundin g under Gra nt BQU2002-00550. The authors ex tend special thanks to Professor Juan Forni es for generous logistical upport.

References I Falve llo L R. Pasc ual I & Tomas M. Inorg chilli ACllI . 229

( 1995) 135.

:!

3

~

:)

6

7

R

9

10

II

FALVELLO et al. : STUDY OF Co (II) COMPLEXES OF 2- IMI DAZOLIDO E 1315

Falve ll o L R, Pascual I. Tomas M & Urriolabeitia E P, J Alii ehelll Soc. I 19 ( 1997) I 1894. Falve ll o L R. Hitchman M A. Palacio F, Pascual I, Schultz A J. Stratemeier H. Tomas M, Urriolabei tia E P & Young D M, J Alii chelll Soc. 121 ( 1999) 2808. Fa lve ll o L R. Gomez J. Pascual I, Tomas M, Urriolabei ti a E P & Schu ltz A J. /ll org Chem , 40 (200 1) 4455. Falvello L R & Tomas M. Chelll CommulI , (1999) 273. Falvello L R. Garde R & Tomas M, J ellist Sci. II (2000) 125. Escorihuela I, Falvello L R & Tomas M, /llorg Chem, 40 (200 1) 636. (a) Tseng S S. Gi rotra R N, Cribbs C M. Sonntang, D L P & Johnson. J L. A CS Symposillm Series, 443 (1991 ) 122; (b) Chelll AiJstr, 114 ( 1991) 122180b. Seebach D. Maetzke T. Petter W, Klotzer B & Plattner D A. J Alii chelll Soc. 113 ( 199 1) 178!. (a) Pereira E R, Sancelme M. Towa J J, Prudhomme M. Marli'e A M. Mousset G & Rapp M, J Alltibiotics, 49 ( 1996) 380: (b) Chell/ AbSlr. 124 (1996) 331893g. (a) Doyle M P. Aldrichimica AC/a, 29 (1996) 3: (b) Chem AiJslr.1 24( 1995)289137m .

12 13

14 15

16

17

18

19

20

21 22

Majeste R J & Trefonas L M. /llorg Chem. ! I ( 1972 ) 1 8.\~.

Tavridou P. Russo U, Marton D, Valle G & Kova ia-Delllciv i D, /llorg chim AC/a, 23 1 (1995) 139. Majeste R J & Trefonas L M. /llorg Chem. 13 ( 1974) I 06~. Brown J N. Pierce A G & Trefonas L M. Illorg Chell!. II (1972) 1830. Diffractometer control program: CAD~/PC Ver,ioll ~ . ().

Nonius by, Delft, The Netherlands 1996. Data were processed on an AlphaStation 200 ~II 66 (OpenVMS/Alpha V6.2), with the program XCAD~B (K. Harms. 1996). SHELXTL Rei. 5.G5/VMS: (Siemens Ana lytical X-ray In struments. Inc .. Madison. Wisconsin ) 1996. SHELXS-97: Forlrall program for crrswl Slmelilre .\Ollilillll. © 1997. George M. Sheldrick. SHELXL-97: FOr/rail program for Cl'vswl Slmc/llre refill eme!ll , © 1997, George M. Sheldri ck. Bondi A. J phl's Chem, 68 ( 1964) 441. (a) Bekaroglu O. Sari saban S. Koray A R & Ziegler M L. I. Natlllforsch. Teil B. 32 (1977) 387: (b) Cambridge Structural Database System, Reference Code AGX ICO.