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Inorganica Chimica Acta 359 (2006) 99–108

Syntheses and structures of photochromic molybdenum(II)and rhodium(II) complexes with

1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene

Jing Han, Hisashi Konaka, Takayoshi Kuroda-Sowa, Masahiko Maekawa,Yusaku Suenaga, Hiromichi Isihara, Megumu Munakata *

Department of Chemistry, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan

Received 10 May 2005; received in revised form 6 August 2005; accepted 20 August 2005Available online 5 October 2005

Abstract

Four novel Mo(II) and Rh(II) complexes with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (cis-dbe) or closed-dbe weresynthesized and characterized. Employing [M(O2CCF3)4] (M =Mo, Rh) with cis-dbe or closed-dbe afforded complex [Mo2(O2CCF3)4-(cis-dbe)](benzene) (1), [Rh2(O2CCF3)4(cis-dbe)](benzene) (2), [{Mo2(O2CCF3)4}2(closed-dbe)] (3), and [Rh2(O2CCF3)4(closed-dbe)]-(p-xylene) (4). The structures of four metal complexes were revealed by X-ray crystallographic analyses and the correlation betweenthe crystal structures and the photochromic performance was discussed. In all complexes, two cyano groups of the ligand bridgedtwo dimetal carboxylates to give a 1-D zigzag infinite chain structure. Upon irradiation with 405 nm light, complex 1 turned into reddishpurple from yellow, and the color reverted to initial yellow on exposure to 563 nm light, indicating the reversible cyclization/ring-openingreaction in the crystalline phase. However, the Rh(II) complex 2 did not display similarities in reaction induced by light, which is attrib-utable to the lower ratio of photoactive anti-parallel conformers compared with complex 1 and coordination effect of metal ions onphotochromism of diarylethenes. The complexes of Rh(II) ions did not exhibit the expected reversible photoinduced behavior.� 2005 Elsevier B.V. All rights reserved.

Keywords: Diarylethene; Photochromism; Crystalline phase; Mo(II) complexes; Rh(II) complexes

1. Introduction

Photochromism is referred to as a photochemicallyreversible transformation of a chemical species betweentwo isomers having different absorption spectra [1–10].Among many known photochromic systems, diarylethenesbearing two thiophene-derived backbones have receivedthe most attention, since they are particularly well suitedas switching units and are able to undergo thermally irre-versible cyclization reactions between open-form andclosed-form when stimulated with UV and visible light,which are useful in optical memory media, nonlinear op-

0020-1693/$ - see front matter � 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2005.08.023

* Corresponding author. Tel.: +81 6 6723 2332x4119; fax: +81 6 67232721.

E-mail address: munakata@chem.kindai.ac.jp (M. Munakata).

tics, switching device applications, and a variety of otherfields [11–17]. In the open-form, the two thiophene ringsare capable of folding into a parallel conformation, whichallows interaction between the two thiophene-appendedmoieties. In the closed-form, these moieties are spacedapart from each other in a rigid conformation. Duringthe cyclization, thiophene rings are required to approacheach other by rotating, as shown in Scheme 1.

We first reported the syntheses and photochromism ofmetal complexes of diarylethenes with a linear copper(I)and silver(I) coordination polymers bridged by the cyanogroups of cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)-ethene (cis-dbe) [18,19]. Recently, metal complexes withother photochromic ligands were synthesized [20–25], butthe reports on the photochromic complexes in thecrystalline phase are still rare. Only the Ag(I) and Cu(I)

CNNC

SS

CNNC

S

405 nm

546 nmS

Scheme 1. Photochromic reaction of cis-dbe.

100 J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108

complexes about cis-dbe have been synthesized so far,which prompted us to try to synthesize other metal ionscomplexes with cis-dbe. Dimolybdenum(II) and dirho-dium(II) trifluoroacetates with metal–metal bond were cho-sen as the metal source since both metal centers can beprimarily coordinated to ligand in the apical position.The dirhodium complex is especially unusual in the factthat it is capable of forming stable diaxial adducts with awide variety of ligands in comparison with other stronglymetal–metal bonded dimetal tetracarboxylates (such asdichromium complex). In the present work, our findingson crystal structures, conformations and the photochromicproperties of four novel metal complexes with cis-dbe orclosed-dbe in crystalline phase stimulate our interest in fur-ther understanding of the photochromic behavior of themetal complexes as well as the coordination effect of metalions on photochromism of diarylethenes.

2. Experimental

2.1. General methods

Unless otherwise indicated, all starting materials wereobtained from commercial suppliers (Aldrich, Tokyo KaseiChemicals, and Kanto Chemicals) and without furtherpurification prior to use. All reactions and manipulationswere carried out under an argon atmosphere. Solvents weredried using standard procedures and distilled under an ar-gon atmosphere prior to use. [Mo2(O2CCF3)4] and[Rh2(O2CCF3)4] were prepared according to the known lit-erature [26,27]. Closed-dbe was obtained by separating thecis-dbe hexane solution irradiated with 405 nm light.

Infrared spectra were recorded as KBr disk on JASCOFT-IR 8000 and FT/IR-430 spectrometers. Absorptionspectra in crystalline state were measured by diffuse reflec-tion using the Kubelka-Munk method on a SHIMADZUUV-2450 spectrometer, and barium sulfate was used as areference. Photoirradiation was carried out using a 150 WXe lamp, and monochromatic light was obtained by pass-ing the light through a monochromator.

2.2. Syntheses

2.2.1. [Mo2(O2CCF3)4(cis-dbe)](benzene) (1)[Mo2(O2CCF3)4] (32.6 mg, 0.05 mmol) and cis-dbe

(49.3 mg, 0.15 mmol) were dissolved in 5 mL benzene and15 mL hexane, respectively. The resultant solution wascarefully introduced into a 7 mm glass tube, which afforded

complex 1 as yellow plate crystals after standing in the darkat ambient temperature for 1 week. Anal. Calc. for Mo2S2-F12O8N2C32H24: C, 36.66; H, 2.31; N, 2.67. Found: C,36.26; H, 2.30; N, 2.72%. IR (KBr pellet, range 4000–400 cm�1): 3034 (w), 2925 (w), 2863 (w), 2234 (w), 1601(s), 1488 (w), 1479 (w), 1442 (w), 1383 (w), 1225 (s), 1192(s), 1159 (s).

2.2.2. [Rh2(O2CCF3)4(cis-dbe)](benzene) (2)The red plate crystals were grown similarly to those of

complex 1 using [Rh2(O2CCF3)4] (44.3 mg, 0.07 mmol) in-stead of [Mo2(O2CCF3)4]. Yield: 34.0 g (47.5%). Anal.Calc. for Rh2S2F12O8N2C32H24: C, 36.18; H, 2.64; N,2.28. Found: C, 36.21; H, 2.40; N, 2.55%. IR(KBr pellet,range 4000–400 cm�1): 3035 (w), 2957 (w), 2926 (w), 2864(w), 2243 (w), 1666 (s), 1551 (w), 1488 (w), 1479 (w),1459 (w), 1441 (m), 1388 (w), 1364 (w), 1233 (s), 1220 (s),1191 (s), 1166 (s).

2.2.3. [{Mo2(O2CCF3)4}2(closed-dbe)2] (3)Complex 3 was obtained similarly to that of complex 1

using closed-dbe and mixed solution of hexane and pentane(2:3) in the place of cis-dbe and hexane, respectively. Theresultant solution was carefully introduced into a 7 mmglass tube, which afforded complex 3 as reddish purplebrick crystals after standing in the dark at ambient temper-ature for 1 week. Anal. Calc. for Mo4S4F24O16N4C52H36:C, 32.18; H, 1.87; N, 2.89. Found: C, 32.29; H, 1.93; N,2.93%. IR (KBr pellet, range 4000–400 cm�1): 3031 (w),2981 (w), 2932 (w), 2905 (w), 2866 (w), 2216 (m), 2186(m), 1608 (s), 1597 (s), 1507 (m), 1445 (m), 1387 (w),1372 (w), 1358 (w), 1226 (s), 1192 (s), 1154 (s).

2.2.4. [Rh2(O2CCF3)4(closed-dbe)](p-xylene) (4)The reddish purple plate crystals were obtained similarly

to those of complex 3 using [Rh2(O2CCF3)4] (39.5 mg,0.06 mmol) and p-xylene (60 mL) in the place of[Mo2(O2CCF3)4] and mixed solution, respectively. Anal.Calc. for Rh2S2F12O8N2C34H30: C, 37.38; H, 2.77; N,2.56. Found: C, 37.82; H, 2.66; N, 2.48%. IR (KBr pellet,range 4000–400 cm�1): 2988 (w), 2929 (w), 2867 (w), 2238(m), 1667 (s), 1503 (m), 1444 (m), 1386 (w), 1373 (w),1225 (s), 1192 (s), 1169 (s).

2.3. X-ray data collection and structure solutions and

refinements

Diffraction data for 1 were collected on a Rigaku AFC-7R automated diffractometer with graphite monochro-mated Cu Ka radiation (k = 1.54178 A). Intensity datawere collected at 296 K using the x–2h scan techniqueand a total of 3543 reflections were collected. The intensi-ties of three representative reflections were measured afterevery 150 reflections and remained constant, and decaycorrection was applied. The linear absorption coefficientl for Cu Ka radiation is 67.86 cm�1. An empirical absorp-tion correction based on azimuthal scans of several

Table 1Crystallographic data for complexes 1–4

Complex 1 2 3 4

Formula Mo2S2F12O8N2C32H24 Rh2S2F12O8N2C32H24 Mo4S4F24O16N4C52H36 Rh2S2F12O8N2C34H28

Formula weight 1048.53 1062.46 1940.84 1090.52Crystal system monoclinic monoclinic triclinic monoclinicSpace group C2/c (#15) C2/c (#15) P�1 ð#2Þ C2/c (#15)a (A) 23.041(4) 22.886(4) 12.500(2) 20.381(4)b (A) 13.368(4) 13.453(1) 13.099(2) 13.723(2)c (A) 17.186(3) 17.925(3) 11.970(1) 16.296(3)a (�) 107.223(3)b (�) 128.103(9) 131.659(5) 95.176(3) 117.898(6)c (�) 112.821(4)V (A3) 4165(1) 4123(1) 1678.0(3) 4028(1)Z 4 4 1 4Dcalc (g/cm

3) 1.672 1.711 1.920 1.798l 6.786 1.002 0.987 1.028Observed reflections [I > 2r(I)] 3225 4076 6189 3610Ra 0.0452 0.0619 0.0343 0.0702Rw

b 0.1272 0.1509 0.0714 0.1349Goodness-of-fit 1.054 1.153 1.046 1.107

a R =P

iFo| � |Fci/P

|Fo|.b Rw ¼ ½

PwðF 2

o � F 2cÞ

2=P

wðF 2oÞ

2�1=2.

Table 2Selected bond lengths (A) and angles (�) for complexes 1–4

Complex 1

Mo(1)–Mo(1) 2.112(1) Mo(1)–O(2) 2.119(4)N(1)–C(6) 1.135(7) Mo(1)–O(3) 2.110(5)Mo(1)–N(1) 2.601(6) Mo(1)–O(4) 2.115(4)Mo(1)–O(1) 2.115(4)

Mo(1)–N(1)–C(6) 169.8(6) Mo(1)–Mo(1)–N(1) 164.6(1)

Complex 2

Rh(1)–Rh(1) 2.4135(7) Rh(1)–O(2) 2.029(4)N(1)–C(6) 1.135(5) Rh(1)–O(3) 2.035(6)Rh(1)–N(1) 2.226(4) Rh(1)–O(4) 2.037(6)Rh(1)–O(1) 2.034(4)

Rh(1)–N(1)–C(6) 172.5(3) Rh(1)–Rh(1)–N(1) 179.2(1)

Complex 3

Mo(1)–Mo(1) 2.1223(4) Mo(1)–O(2) 2.133(2)N(1)–C(3) 1.150(4) Mo(1)–O(3) 2.110(2)N(2)–C(4) 1.150(4) Mo(1)–O(4) 2.118(3)Mo(1)–O(1) 2.121(2) Mo(1)–N(1) 2.553(2)

Mo(1)–N(1)–C(3) 158.5(3)Mo(2)–N(2)–C(4) 107.1(3) Mo(1)–Mo(1)–N(1) 166.49(6)

Complex 4

Rh(1)–Rh(1) 2.419(1) Rh(1)–O(2) 2.042(5)N(1)–C(6) 1.132(8) Rh(1)–O(3) 2.033(4)Rh(1)–N(1) 2.200(6) Rh(1)–O(4) 2.035(4)Rh(1)–O(1) 2.039(5)

Rh(1)–N(1)–C(6) 166.3(6) Rh(1)–Rh(1)–N(1) 177.6(1)

J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108 101

reflections and a symmetry-related absorption correctionwas applied to complex 1. In addition, a correction of sec-ondary extinction was applied. The data were corrected forLorentz and polarization effects. For 2, 3 and 4, a suitablecrystal of each was attached to the end of a glass fiber andmounted on a Quantum CCD area detector coupled with aRigaku MSC Mercury CCD diffractometer with graphitemonochromated Mo Ka radiation (k = 0.71069 A). Theintensity data were collected at 150 K for 3 and 4 and296 K for 2 using the x scan technique and a total of4696, 7372, and 4565 reflections were collected for com-plexes 2–4, respectively. No decay correction was applied.The linear absorption coefficient l for Mo Ka radiationis 9.87, 10.02, and 10.28 cm�1, respectively. A symmetry-re-lated absorption correction was applied. In addition, a cor-rection of secondary extinction was applied for 2. The datawere corrected for Lorentz and polarization effects.

The structures were solved by direct methods followedby subsequent Fourier calculations [28]. The non-hydrogenatoms were refined anisotropically. The coordinates of thehydrogen atoms in methyl group were treated as ridingatoms at a distance of 0.96 A, while the positions of theother hydrogen atoms including the hydrogen atoms in dis-ordered methyl group were treated at a distance of 0.95 A.For the minor disordered part of complex 2, S(1) and S(2)were refined anisotropically, and C(17), C(4), C(9) andC(18) were refined isotropically. The final cycle of thefull-matrix least-squares refinement was based on 3225,4076, 6189, and 3610 observed reflections and 266, 272,475, and 276 variable parameters for 1–4, respectively,converged with the unweighted and weighted agreementfactors of R =

PiFo| � |Fci/

P|Fo| and Rw ¼ ½

PwðF 2

o�F 2

cÞ2=P

wðF 2oÞ

2�1=2. The atomic scattering factors andanomalous dispersion terms were taken from the Interna-tional Tables for X-ray Crystallography, vol. IV [29]. All

calculations were performed using the teXsan crystallo-graphic software package [30]. Details of the X-ray exper-iments and crystal data are summarized in Table 1.Selected bond lengths and bond angles are given in Table 2.

102 J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108

2.4. Photochromic behavior of the complexes

The photoirradiation process of cis-dbe and four me-tal complexes was followed by electronic spectroscopy.The absorption spectra in the crystalline state were mea-sured by diffuse reflection using barium sulfate as thereference.

Fig. 1. Crystal structure of 1. (a) ORTEP view with atomic labeling s

3. Results and discussion

3.1. Structural characterizations

Four Mo(II) and Rh(II) coordination compounds wereprepared by the reaction of the dimetal trifluoroacetates([Mo2(O2CCF3)4] and [Rh2(O2CCF3)4]) with cis-dbe or

cheme, showing 50% thermal ellipsoids. (b) 1-D chain structures.

J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108 103

closed-dbe in solvents, such as benzene, pentane and p-xylene. The structures of these complexes were determinedby X-ray crystallographic analyses and are shown in Figs.1–4.

According to the crystallographic studies, complexes 1

and 2, which have the same cis-dbe ligand but different me-tal ions, are crystallized in the same space group. The crys-tal structures of the two complexes show that each metalions of dimetal trifluoroacetates is coordinated with cyanogroup of cis-dbe to form an infinite 1-D zigzag polymericchain, as shown in Figs. 1 and 2. This is quite different fromthe coordination modes of Cu(I) complex with cis-dbe,where the metal center is coordinated with one cyanogroup of four different cis-dbe molecules and Ag(I) com-plex with cis-dbe where the metal center is coordinatedwith one cyano group as well as one thienyl S atom of

Fig. 2. Crystal structure of 2. (a) ORTEP view with atomic labelingscheme, showing 50% thermal ellipsoids. (b) 1-D chain structures.

two different cis-dbe [11,12]. In complexes 1 and 2, thereis a p–p interaction between the thiophene rings of theadjacent polymeric chains with a distance of 3.57 A in 1

and 3.55 A in 2, respectively. cis-dbe in complex 1 adoptsan anti-parallel conformation in which photocyclizationproceeds in a conrotatory fashion [31–39]. The distanceof 3.53 A between the reactive carbon atoms in complex1 is short enough to have a cyclization/cycloreversion pho-tochromic reaction in the crystalline phase [1]. However,complex 2 contains both photoreactive anti-parallel (A)and photoinactive parallel (B) conformers, which coexistedin the ratio of 0.75/0.25. The distance between the reactivecarbon atoms is 3.56 A for photoactive anti-parallel con-formers of complex 2.

The complexes [{Mo2(O2CCF3)4}2(closed-dbe)] (3) and[Rh2(O2CCF3)4(closed-dbe)](p-xylene) (4) were synthesizedusing closed-dbe in the place of cis-dbe. X-ray crystallo-graphic analyses revealed that complexes 3 and 4 have asimilar coordination mode as complexes 1 and 2. In bothcomplexes, the metal ions are coordinated with the two cy-ano groups of the closed-dbe ligand to give a 1-D zigzagpolymeric chain, as shown in Figs. 3 and 4. In complex3, two bond angles of C–N–Mo are, however, notably dif-ferent, being 158.5(3)� and 107.1(2)�, and subsequentlycomplex 3 has an asymmetric structure, which differs fromother three symmetric complexes.

The Mo–Mo distances of both Mo(II) complexes are2.1119(9), 2.1140(5) and 2.222(4) A in complexes 1 and 3,respectively, which are a little longer than the value of2.090(4) A obtained from the parent compound[Mo2(O2CCF3)4] [40] and are shorter than the 2.129(2) Abond distance in the pyridine complex [Mo2(O2CCF3)4-(py)2] [41]. The difference of Rh–Rh distance is less smallbetween complexes 2 and 4. The bond distances of C„Nare 1.133(7) A (1), 1.135(5) A (2), 1.150(4) A (3), and1.132(8) A (4). The crystallographic parameters as well aslengths and angles of selected bonds of complexes 1–4 aresummarized in Tables 1 and 2.

3.2. Photochromism in the crystalline phase

The yellow complex 1 of open-form is transformed intothe reddish purple closed-form by irradiation with 405 nmUV light. The isosbestic point in spectral changes slightlyshifts with the irradiation in more than 30 min (Fig. 5).The closed-ring isomers are converted back to the open-ringupon irradiation with 563 nm light, accompanying littledrift of isosbestic point. Thus, complex 1 shows the revers-ible photochromic reactivity, but both two isomers are notvery stable on long time irradiation. Complex 1 displaysthe normal reversible cyclization/ring-opening reaction incrystalline phase although the coordination mode and crys-tal structure of complex 1 are different from those of Cu(I)and Ag(I) complexes with cis-dbe. Indeed, the distancebetween the reactive carbons of cis-dbe is as short as thoseof the Cu(I) complex (3.68 A) and Ag(I) complexes (3.45–3.58 A) (Table 3). These facts indicate that the complexation

Fig. 3. Crystal structure of 3. (a) ORTEP view with atomic labeling scheme, showing 50% thermal ellipsoids. (b) 1-D chain structures.

104 J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108

with metal ions does not prohibit the photochromicreactions of diarylethene units in the crystalline phase.

cis-dbe of complex 2 is not essentially transformed intothe closed-form with irradiation of 405 nm light which isdifferent from the yellow complex 1, although the crystalstructures of both complexes are similar each other. Thedistances between the reactive carbon atoms which controlthe photochromic reactivity other than steric substituenteffect [1] are similar, being 3.53 and 3.56 A for complex 1and photoactive anti-parallel conformers of complex 2,respectively. There is also a p–p interaction between thienylgroups of neighboring chains in complex 2, similarly tocomplex 1. Only the anti-parallel conformer is packedin complex 1, whereas three kinds of conformers coexist incomplex 2. The ratio of two disordered conformers A/Bis 0.75/0.25. If the conformation of the two thiophen ringsof cis-dbe has no correlation, three types of conformers

(photoreactive anti-parallel (a) = AA, non-reactive parallelconformers (b) = AB and non-reactive anti-parallel(c) = BB) coexist in the following mol ratio: 0.56/0.38/0.06 (i.e., A · A/2 · A · B/B · B) according to the Proba-bility Theory of mathematics science (Scheme 2). Con-former c is photochemically inactive although it is in theanti-parallel conformation because diarylethenes undergoa 1,3,5-hexatriene to cyclohexadiene-type photochromicreaction by alternating irradiation with appropriate wave-length light. Therefore, in complex 2 about 56% of mole-cules adopt a photoactive anti-parallel conformation,while 44% of molecules adopt a photoinactive parallel oranti-parallel conformations. According to Woodward–Hoffmann rules, the photocyclization reaction shouldproceed only from the photoactive anti-parallel conformer,and consequently a population of the parallel conformerdecreases the quantum yield of the photochromic reaction

Fig. 4. Crystal structure of 4. (a) ORTEP view with atomic labeling scheme, showing 50% thermal ellipsoids. (b) 1-D chain structures.

J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108 105

[42–44,5,7]. This is partly responsible for the unexpectedidentical photoreactive behavior in complex 2. It is worth-while to note that 1,2-bis(2,4-dimethyl-3-thienyl)perfluoro-cyclopentene can undergo photochromism with only 17%ratio of anti-parallel conformers, which is significantlylower than the case of complex 2 [38]. The existence of44% photoinactive conformers is partially reflected in theobserved photoreactive behavior in complex 2. This findingis of interest in connection with coordination effect of metalions on photochromism of diarylethenes.

Complex 3 of closed-form (reddish purple) shows amaximum absorbance at 550 nm, which showed a batho-chromic shift upon complexation (484 nm for free ligand),as shown in Fig. 6, and is a little different from that of theclosed-ring form obtained by photoirradiation on 1. This

may be attributable to the photostationary state betweencis-dbe and closed-dbe, that is, the kmax of 560 nm repre-sents a transient intermediate where the conversion ratioto closed-dbe is smaller than 100%, judging from thepeak-height and shape. Complex 3 is transformed intothe open-form (yellow color) with irradiation with550 nm light. On the other hand, the resulting open-formis not returned to the original closed-form but to a greencomplex with kmax at 750 nm. This indicates that the struc-ture of the open-ring complex is changed with the furtherirradiation.

Similarly to complex 3, reddish purple complex 4 ofclosed-form with kmax = 574 nm is transformed into theyellow open-form upon irradiation with 574 nm lightaccompanying the little shift of isosbestic point in the

Fig. 5. Absorption spectral change of [Mo2(O2CCF3)4(cis-dbe)](benzene)(1) by photoirradiation in the crystalline phase: (a) open-form wastransformed to closed-form with 405 nm light and irradiation times are 0,1, 5, 10, 30, 60, 120, 180 and 420 min. (b) Closed-form was transformed toopen-form with 563 nm light and irradiation times are 0 s, 5 s, 1 min,60 min and 180 min.

Table 3Comparison of metal complexes with cis-dbe

Complex Stacking Reactive C–C distance Reference

Metal cations Ligand p–p (A) C–C (A)

Mo(II) cis-dbe 3.57 3.53 this workRh(II) cis-dbe 3.55 3.56 this workCu(I) cis-dbe 3.68 [18]Ag(I) cis-dbe 3.36–3.59 3.45–3.58 [19]

SS

NN

SS

NN NN

S

anti-parallel(56%, reactive)

parallel(38%, non reactive)

(c)(b)(a) anti-parallel(6%, non reactive)

S

Scheme 2. Conformations in complex 2.

Fig. 6. Absorption spectral change of [{Mo2(O2CCF3)4}2(closed-dbe)2](3) by photoirradiation in the crystalline phase: (a) closed-form wastransformed to open-form with 550 nm light and irradiation times are 0,0.5, 1, 2, 3, 4, 5, 10 and 30 min. (b) Further irradiation with 550 nm lightand irradiation times are 30, 60, 300, 600, 1200 and 1800 min.

106 J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108

spectral changes. On the other hand, the resulting open-form complex is not transformed into the open-form withexposure to 405 nm light, Fig. 7. The absorption maximumalso showed a bathochromic shift in comparison with the

closed-dbe, which may be ascribed to an increase in thestrain upon complexation [24,25].

The kmax, 550 nm (3) and 574 nm (4), of two closed-dbecomplexes shifts to longer wavelength compared with themetal-free closed-dbe (484 nm). All the complexes withclosed-dbe, 3 and 4, are converted into the correspondingopen-form isomer. Two cis-dbe complexes also have a sim-ilar kmax shift to Ag(I) complexes with cis-dbe [19], whereas

Fig. 7. Absorption spectral change of [Rh2(O2CCF3)4(closed-dbe)](p-xylene) (4) by photoirradiation in the crystalline phase: open-formwas transformed to closed-form with 405 nm light and irradiation timesare 0, 1, 10, 60, 300, 600 and 780 min.

J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108 107

complex 2 does not exhibit the reversible photochromicbehavior.

4. Conclusions

Four molybdenum(II) and rhodium(II) complexes withcis-dbe or closed-dbe were prepared and their coordinationstructures and photochromic properties were studied.X-ray crystallographic analyses showed that the metal ionsare coordinated to two cyano groups of all complexes togive a 1-D chain structure. Complex 1 indicated the normalphotochromic behavior while complex 2 was not trans-ferred to the closed form, which partially originates fromthe existence of non-reactive parallel and anti-parallel con-formations although both have the similar crystal struc-tures and distance between the reactive carbon atoms.This indicates our hope on further investigation on the cor-relation of coordination effect of metal ions on photochro-mism of diarylethenes. Cu(I), Ag(I), and Mo(II)coordination polymers with cis-dbe exhibit a reversiblephotochromic reaction in the crystalline phase, whereasthe coordination of cis-dbe and closed-dbe to Rh(II) isnot always advantageous to the reversible cyclization reac-tion in the solid state. Different anions of dirhodium carb-oxylates will be adopted to change the coordinationproperty of rhodium and its effect on the coordinationmode as well as photochromic performance will be investi-gated in the later program.

5. Supplementary materials

Crystallographic data for the X-ray crystal structuralanalysis have been deposited with the Cambridge Crystal-lographic Data Center, Nos. (0155) 270017 for complex1, 270019 for complex 2, 270018 for complex 3 and

270020 for complex 4, respectively. Copies of this informa-tion may be obtained free of charge from The Director,CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:+44 1233 336 033; e-mail: deposit@ccdc.cam.ac.uk orwww: http://www.ccdc.cam.ac.uk).

Acknowledgments

This work was partially supported by a Grant-in-Aid forScience Research (Nos. 14340211 and 13874084) from theMinistry of Education, Science, Sports and Culture ofJapan.

References

[1] S. Kobatake, K. Uchida, E. Tsuchida, M. Irie, Chem. Commun.(2002) 2804.

[2] M. Irie, T. Lifka, S. Kobatake, N. Kato, J. Am. Chem. Soc. 122(2000) 4871.

[3] S. Kobatake, M. Irie, Bull. Chem. Soc. Jpn. 77 (2004) 195.[4] S. Kobatake, S. Kuma, M. Irie, Bull. Chem. Soc. Jpn. 77 (2004) 945.[5] M. Irie, M. Mohri, J. Org. Chem. 53 (1998) 803.[6] M. Irie, T. Lifka, K.S. Kobatake, Y. Shindo, Chem. Commun.

(1999) 747.[7] K. Uchida, Y. Nakayama, M. Irie, Bull. Chem. Soc. Jpn. 63 (1990)

1311.[8] M. Morimoto, S. Kobatake, Chem. Eur. J. 9 (2003) 621.[9] K. Higashiguchi, K. Matsuda, M. Irie, Angew. Chem. Int. Ed. 42

(2003) 3537.[10] S. Kawauchi, H. Yoshida, N. Yamashina, M. Ohira, S. Saeda, M.

Irie, Bull. Chem. Soc. Jpn. 63 (1990) 267.[11] H. Tian, S.J. Yang, Chem. Soc. Rev. 33 (2004) 85.[12] T. Yamada, S. Kobatake, K. Muto, M. Irie, J. Am. Chem. Soc. 122

(2000) 1589.[13] D.V. Kozlov, F.N. Castellano, J. Phys. Chem. A 108 (2004) 10619.[14] S.H. Kawasi, S.L. Gilat, R. Ponsinet, Chem. Eur. J. 1 (1995) 285.[15] S. Fraysse, C. Coudret, J.-P. Launay, Eur. J. Inorg. Chem. 39 (2000)

1581.[16] S.L. Gilat, S.H. Kawasi, J.-M. Lehn, Chem. Eur. J. 1 (1995) 275.[17] B. Qin, R.X. Yao, X.L. Zhao, H. Tian, Org. Biomol. Chem. 12

(2003) 2187.[18] M. Munakata, L.P. Wu, T. Kuroda-Sowa, M. Maekawa, Y. Suenaga,

K. Furuichi, J. Am. Chem. Soc. 118 (1996) 3305.[19] H. Konaka, L.P. Wu, M. Munakata, T. Kuroda-Sowa, M. Maekawa,

Y. Suenaga, Inorg. Chem. 42 (2003) 1928.[20] T. Yutaka, I. Mori, M. Kurihara, J. Mizutani, K. Kubo, S. Furusho,

K.Matsumura, N. Tamai, H. Nishihara, Inorg. Chem. 40 (2001) 4986.[21] T. Yutaka, I. Mori, M. Kurihara, N. Tamai, H. Nishihara, Inorg.

Chem. 42 (2003) 6306.[22] J. Otsuki, N. Omokawa, K. Yoshiba, I. Yoshikawa, T. Akasaka, T.

Suenobu, T. Takido, K. Araki, S. Fukuzumi, Inorg. Chem. 42 (2003)3057.

[23] S. Hirose, S. Hayami, Y. Maeda, Bull. Chem. Soc. Jpn. 73 (2000)2059.

[24] K. Matsuda, K. Akayama, M. Irie, Chem. Commun. (2001) 363.[25] K. Matsuda, K. Takayama, M. Irie, Inorg. Chem. 43 (2004) 482.[26] F.A. Cotton, J.G. Norman Jr., J. Coord. Chem. 1 (1971) 161.[27] G.A. Rempel, P. Legdins, H. Smith, G. Wilkinson, Inorg. Synth. 13

(1971) 90.[28] P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, R. de.

Gelder, R. Israel, J.M.M. Smits, The DIRDIF-94 Program System:Technical Report of the Crystallography Laboratory, University ofNijmegen, The Netherlands, 1994.

[29] D.T. Cromer, J.T. WaerInternational Tables for X-ray Crystallogra-phy, vol. IV, The Kynoch Press, Birmingham, England, 1974.

108 J. Han et al. / Inorganica Chimica Acta 359 (2006) 99–108

[30] Crystal Structure Analysis Package, Molecular Structure Corpora-tion, 1985 and 1992.

[31] S. Kobatake, M. Yamada, T. Yamada, M. Irie, J. Am. Chem. Soc.121 (1999) 8450.

[32] M. Irie, K. Uchida, T. Eriguchi, H. Tsuzuki, Chem. Lett. (1995) 899.[33] S. Kobatake, T. Yamada, K. Uchida, N. Kato, M. Irie, J. Am.

Chem. Soc. 121 (1999) 2380.[34] S. Kobatake, K. Shibata, K. Uchida, M. Irie, J. Am. Chem. Soc. 122

(2000) 12135.[35] T. Kodani, K. Matsuda, T. Yamada, S. Kobatake, M. Irie, J. Am.

Chem. Soc. 122 (2000) 9631.[36] M. Irie, O. Miyatake, K. Uchida, J. Am. Chem. Soc. 114 (1992) 8715.[37] T. Yamada, K. Muto, S. Kobatake, M. Irie, J. Org. Chem. 66 (2001)

6164.

[38] T. Yamada, S. Kobatake, M. Irie, Bull. Chem. Soc. Jpn. 75 (2002)167.

[39] J. Ern, A.T. Bens, H.-D. Martin, S. Mukamel, S. Tretiak, K.Tsyganeko, K. Kuldova, H.P. Trommsdorff, C. Kryschi, J. Phys.Chem. A 105 (2001) 1741.

[40] F.A. Cotton, C.E. Rice, G.W. Rice, J. Am. Chem. Soc. 99 (1977)4704.

[41] F.A. Cotton, J.G. Norman Jr., J. Am. Chem. Soc. 94 (1972) 5697.[42] A. Goldberg, A. Murakami, K. Katsuya, T. Kobayashi, S. Nakam-

ura, K. Uchida, H. Sekiya, T. Fukaminato, T. Kawai, S. Kobatake,M. Irie, J. Phys. Chem. A 107 (2003) 4982.

[43] K. Uchida, E. Tsuchida, Y. Aoi, S. Nakamura, M. Irie, Chem. Lett.(1999) 63.

[44] S. Nakamura, M. Irie, J. Org. Chem. 53 (1998) 6136.