CRYSTAL GROWTH & DESIGN
Supramolecular Isomerism in Self-Assembled Complexes from 4,4′-Dipyridyl Disulfide and M(hfac)2: Coordination Polymers (M ) Mn) and Metallamacrocycles (M ) Co, Ni)
2005 VOL. 5, NO. 1 243-249
Ryo Horikoshi,† Tomoyuki Mochida,‡ Makoto Kurihara,† and Masahiro Mikuriya*,† Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan, and Department of Chemistry, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan Received March 10, 2004
ABSTRACT: Correlations between the reaction conditions and resultant structures have been investigated in detail for supramolecules of M(hfac)2 (hfac ) 1,1,1,5,5,5-hexafluoroacetylacetonate) with 4pds (4pds ) 4,4′-dipyridyl disulfide). It was revealed that coordination polymers are selectively obtained for M ) Mn and Cu and metallamacrocycles are obtained for M ) Co and Ni. The Mn complex [Mn(hfac)24pds]n was found to exhibit supramolecular isomerism depending on the reaction solvent, forming compounds with zigzag achiral chains (1) from methanol and helical chiral chains (2) from tetrachloromethane. The metallamacrocycles [M(hfac)2(4pds)]2‚ 4CHCl3 (M ) Co 3; M ) Ni 4) and [M(hfac)2(4pds)]2‚H2O (M ) Co 5; M ) Ni 6) are composed of two M(hfac)2 units and two ligands with the same chirality. The macrocycles are chiral and change their shape slightly depending on the guests accommodated above and below the cavities. Introduction Supramolecular engineering of assembled metal complexes has become an important area of research that has received considerable attention in this decade.1-13 In particular, rational design and construction of supramolecular architectures have been pursued and demonstrated in some systems.14-18 The idea of rational design is indeed fascinating, but it is questionable to what extent this idea is effective. To probe the limits and possibilities of supramolecular engineering, the choice of a simple model system would be advantageous. For example, if one chose a bidentate ligand with a 90° bent structure and a metal center that has two bonding sites, the combination of features should produce topologically simple but dimensionally diverse supramolecules. Following this strategy, we have performed a detailed investigation on the supramolecular formation of 4,4′-dipyridyl disulfide (4pds) with M(hfac)2 (hfac ) 1,1,1,5,5,5-hexafluoroacetylacetonate, M ) Mn, Cu, Ni, and Co). M(hfac)2 is labile and can assume either cis or trans configurations. 4pds is a simple bidentate ligand that has a characteristic 90° bent structure and accompanying axial chirality, generating the P- and M-forms of enantiomer (Scheme 1).19-21 Indeed, this ligand has been frequently used in supramolecular construction and has produced a variety of diverse selfassembled structures upon complexation with various metal ions.22-26 However, the choice of M(hfac)2 as the metal center strictly limits the topological diversity of the system and allows one to examine the consequence of supramolecular isomerization. Previously, we demonstrated that the combination of 4pds with M(hfac)2 (M ) Mn, Cu) produces coordination * To whom correspondence should be addressed. Fax: +81-79-5659077. E-mail:
[email protected]. † Kwansei Gakuin University. ‡ Toho University.
Scheme 1.
Enantiomers of 4pds
polymers that exhibit zigzag and helical structures, respectively.19 The latter compound was also prepared by Stang et al.24 Here, we have carefully investigated the reaction conditions and extended the metal species studied; we found that coordination polymers were selectively obtained for M ) Mn and Cu and metallamacrocycles for M ) Co and Ni. Moreover, changing the reaction solvent was found to induce structural change in the resultant supramolecules. Because construction of macrocyclic supramolecular coordination complexes has drawn special interest from the viewpoint of host-guest chemistry,7,14,16 we also focus on the guest dependence of the metallamacrocycle complexes. Experimental Section General Methods. All reagents and solvents were commercially available. The preparation and structure of helix[Mn(hfac)2(4pds)]n (1) was reported previously.19 The solvent dependence of the reaction of M(hfac)2 (M ) Mn, Cu, Co, and Ni) with 4pds was investigated by measuring the powder X-ray diffraction patterns of the products on a Rigaku RINT 2000 or by measuring the cell parameters of single crystals. Infrared spectra were recorded on a JASCO MFT-2000 spectrometer as KBr pellets. Thermogravimetric (TG) analysis was performed under a nitrogen atmosphere at a heating rate of 5 °C/min on a Seiko TG/DTA 220U, in the temperature range of 25-400 °C. Elemental analysis was performed on vacuumdried, guest-free samples. Helix-[Mn(hfac)2(4pds)]n (2). A solution of Mn(hfac)2‚ 2H2O (50 mg, 1 × 10-4 mol) in CCl4 (2 mL)/diethyl ether (2
10.1021/cg0499109 CCC: $30.25 © 2005 American Chemical Society Published on Web 08/24/2004
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Table 1. Crystallographic Data for 2-6 compd CCDC no. empirical formula formula weight crystal size (mm) crystal system space group temperature (K) a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z Fcalcd (g cm-3) µ (mm-1) F(000) 2θmax (°) R (int) total reflections unique reflections R1, wR2 [I > 2σ (I)]a goodness-of-fit on F2 max/min electron density (e Å-3)
2 223062 C20H10F12MnN2O4S2 689.36 0.7 × 0.6 × 0.2 monoclinic P21/c (no. 14) 296 7.8856(10) 16.203(2) 20.848(3) 90 91.425(3) 90 2662.9(6) 4 1.720 0.767 1364 55 0.0287 6049 3362 0.0391, 0.0748 1.066 0.346/-0.160
3 223060 C44H24Cl12Co2F24N4O8S4 1864.17 0.7 × 0.5 × 0.2 monoclinic C2/c (no. 15) 150 28.560(4) 12.3988(19) 24.118(4) 90 123.242(10) 90 6975.1(19) 4 1.775 1.169 3672 55 0.0384 7760 6126 0.0435, 0.1092 1.032 0.933/-0.943
4 223061 C44H24Cl12F24N4Ni2O8S4 1863.73 0.5 × 0.3 × 0.2 monoclinic C2/c (no. 15) 150 28.73(2) 12.416(9) 24.182(18) 90 125.19(2) 90 7050(9) 4 1.756 1.220 3680 55 0.0446 5081 4249 0.0595, 0.1450 1.056 1.880b/-1.554b
5 226171 C40H22Co2F24N4O9S4 1404.73 0.5 × 0.2 × 0.2 orthorhombic Fddd (no. 70) 296 14.151(2) 36.370(5) 48.078(7) 90 90 90 24744(6) 8 1.508 0.791 11134 55 0.0435 7363 3305 0.0778, 0.2404 0.912 1.071c/-0.452
6 227461 C40H22F24N4Ni2O9S4 1404.25 0.5 × 0.5 × 0.2 orthorhombic Fddd (no. 70) 296 14.1724(7) 36.1530(19) 47.621(2) 90 90 90 24400(2) 8 1.529 0.857 11168 55 0.0407 7344 4027 0.0728, 0.2147 0.926 0.912/-0.584
a R ) ∑||F | - |F ||/∑|F |; R ) [∑w(F 2 - F 2)2/∑w(F 2)2]1/2. b Because of the disordered CHCl molecule. c A distance of 3.60 Å away 1 o c o w o c o 3 from F(1).
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2-4 2 Mn-N(1) Mn-O(1) Mn-O(3) N(1)-Mn-N(2) N(1)-Mn-O(2) N(1)-Mn-O(4) N(2)-Mn-O(2) N(2)-Mn-O(4) O(1)-Mn-O(3) O(2)-Mn-O(3) O(3)-Mn-O(4)
2.2282(18) 2.1398(15) 2.1861(16) 92.60(7) 95.12(6) 99.28(6) 170.13(6) 88.32(6) 85.26(6) 85.02(6) 82.23(6)
Co-N(1) Co-O(1) Co-O(3) N(1)-Co-N(2) N(1)-Co-O(2) N(1)-Co-O(4) N(2)-Co-O(2) N(2)-Co-O(4) O(1)-Co-O(3) O(2)-Co-O(3) O(3)-Co-O(4)
2.134(2) 2.0595(19) 2.090(2) 89.35(9) 91.52(8) 87.94(8) 178.07(8) 91.77(8) 92.13(8) 87.61(8) 87.86(7)
Ni-N(1) Ni-O(1) Ni-O(3) N(1)-Ni-N(2) N(1)-Ni-O(2) N(1)-Ni-O(4) N(2)-Ni-O(2) N(2)-Ni-O(4) O(1)-Ni-O(3) O(2)-Ni-O(3) O(3)-Ni-O(4)
2.096(4) 2.057(4) 2.072(4) 90.34(16) 91.49(16) 88.70(15) 178.14(15) 90.80(15) 90.84(15) 86.83(15) 89.62(14)
Mn-N(2) Mn-O(2) Mn-O(4) N(1)-Mn-O(1) N(1)-Mn-O(3) N(2)-Mn-O(1) N(2)-Mn-O(3) O(1)-Mn-O(2) O(1)-Mn-O(4) O(2)-Mn-O(4)
2.2695(18) 2.1562(15) 2.1496(15) 93.23(7) 178.46(7) 90.22(6) 87.09(6) 83.23(6) 167.46(6) 96.47(6)
Co-N(2) Co-O(2) Co-O(4) N(1)-Co-O(1) N(1)-Co-O(3) N(2)-Co-O(1) N(2)-Co-O(3) O(1)-Co-O(2) O(1)-Co-O(4) O(2)-Co-O(4)
2.140(2) 2.094(2) 2.0578(18) 92.05(8) 175.71(8) 90.04(8) 91.66(8) 88.20(7) 178.19(8) 89.99(8)
Ni-N(2) Ni-O(2) Ni-O(4) N(1)-Ni-O(1) N(1)-Ni-O(3) N(2)-Ni-O(1) N(2)-Ni-O(3) O(1)-Ni-O(2) O(1)-Ni-O(4) O(2)-Ni-O(4)
2.097(4) 2.072(4) 2.049(3) 90.81(16) 177.72(15) 90.27(16) 91.22(16) 89.98(15) 178.83(15) 88.96(15)
3
4
mL) was added to a solution of 4pds (22 mg, 1 × 10-4 mol) in CCl4 (2 mL). After the mixture was stirred for 5 min, yellow powders were formed. The yellow precipitate was recrystallized from methanol to give 2 as yellow crystals (37 mg, 48% yield).
Anal. calcd % (found %) for C20H10F12MnN2O4S2: C, 34.85 (34.95); H, 1.46 (1.68); N, 4.06 (3.87). IR νKBr (cm-1): 3055w, 1653s, 1590s, 1553s, 1526s, 1480s, 1419s, 1254s, 1196s, 1140s, 1015s, 796s, 711m, and 663m. [Co(hfac)2(4pds)]2‚4CHCl3 (3). A solution of Co(hfac)2‚2H2O (50 mg, 1 × 10-4 mol) in CHCl3 (2 mL)/diethyl ether (2 mL) was added to a solution of 4pds (22 mg, 1 × 10-4 mol) in CHCl3 (2 mL). After the solution stood for a week, orange crystals were formed in a 71% yield, which were suitable for X-ray analysis. Anal. calcd % (found %) for [Co(hfac)2(4pds)]2 ) [C40H20Co2F24N4O8S4]: C, 34.65 (34.75); H, 1.45 (1.68); N, 4.04 (3.83). IR νKBr (cm-1): 3104w, 3068w, 1639s, 1591s, 1557s, 1530s, 1490s, 1413s, 1255s, 1199s, 1140s, 1092s, 811m, 713m, and 670m. [Ni(hfac)2(4pds)]2‚4CHCl3 (4). This material was prepared as described for 3 using 4pds (22 mg, 1 × 10-4 mol) and Ni(hfac)2‚2H2O (50 mg, 1 × 10-4 mol), yielding blue-green crystals in a 44% yield. Anal. calcd % (found %) for [Ni(hfac)2(4pds)]2 ) [C40H20F24N4Ni2O8S4]: C, 34.66 (34.77); H, 1.45 (1.72); N, 4.04 (3.92). IR νKBr (cm-1): 3106w, 1645s, 1595s, 1552s, 1524s, 1482s, 1418s, 1257s, 1200s, 1146s, 795m, 715m, and 671m. [Co(hfac)2(4pds)]2‚H2O (5). A solution of Co(hfac)2‚2H2O (50 mg, 1 × 10-4 mol) in CCl4 (2 mL) was added to a solution of 4pds (22 mg, 1 × 10-4 mol) in diethyl ether (4 mL). The reaction mixture was stirred for 30 min, and then, the solution was evaporated to dryness. The product was redissolved in diethyl ether. After the solution stood for a week, orange crystals were formed in an 86% yield, which were suitable for X-ray analysis. Anal. calcd % (found %) for [Co(hfac)2(4pds)]2 ) [C40H20Co2F24N4O8S4]: C, 34.65 (34.69); H, 1.45 (1.61); N, 4.04 (3.75). IR νKBr (cm-1): 3140w, 3106w, 3063w, 1643s, 1593s, 1555s, 1527s, 1485s, 1418s, 1256s, 1210s, 1149s, 1020s, 813s, 795m, 764m, 714m, and 668m. Recrystallization of 5 from chlorobenzene and tetrachloromethane afforded orange microcrystalline solids, which are assumed to be [Co(hfac)2(4pds)]2‚H2O‚C6H5Cl (5‚PhCl) and [Co(hfac)2(4pds)]2‚H2O‚CCl4 (5‚CCl4), respectively. [Ni(hfac)2(4pds)]2‚H2O (6). This material was prepared by as described for 5 using 4pds (22 mg, 1 × 10-4 mol) and Ni(hfac)2‚2H2O (50 mg, 1 × 10-4 mol), yielding blue-green crystals in a 69% yield. Anal. calcd % (found %) for [Ni(hfac)2-
Complexes from 4,4′-Dipyridyl Disulfide and M(hfac)2
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Table 3. Selected Bond Lengths (Å) and Angles (deg) for 5 and 6 Co(1)-N(1) Co(1)-O(1) Co(1)-O(2) Co(2)-N(2) Co(2)-O(3) Co(2)-O(4) N(1)-Co(1)-N(1)#1 N(1)-Co(1)-O(1)#1 N(1)-Co(1)-O(2)#1 N(1)#1-Co(1)-O(1)#1 N(1)#1-Co(1)-O(2)#1 O(1)-Co(1)-O(2) O(1)#1-Co(1)-O(2) O(2)-Co(1)-O(2)#1 N(2)-Co(2)-O(3) N(2)-Co(2)-O(4) N(2)#1-Co(2)-O(3) N(2)#1-Co(2)-O(4) O(3)-Co(2)-O(3)#1 O(3)-Co(2)-O(4)#1 O(3)#1-Co(2)-O(4)#1
5 2.124(5) Co(1)-N(1)#1 2.041(4) Co(1)-O(1)#1 2.079(4) Co(1)-O(2)#1 2.146(4) Co(2)-N(2)#1 2.101(4) Co(2)-O(3)#1 2.062(4) Co(2)-O(4)#1 92.7(3) N(1)-Co(1)-O(1) 88.77(17) N(1)-Co(1)-O(2) 177.19(18) N(1)#1-Co(1)-O(1) 94.51(17) N(1)#1-Co(1)-O(2) 87.57(19) O(1)-Co(1)-O(1)#1 88.43(18) O(1)-Co(1)-O(2)#1 88.29(18) O(1)#1-Co(1)-O(2)#1 92.3(3) N(2)-Co(2)-N(2)#1 170.66(15) N(2)-Co(2)-O(3)#1 94.42(15) N(2)-Co(2)-O(4)#1 91.12(16) N(2)#1-Co(2)-O(3)#1 85.18(15) N(2)#1-Co(2)-O(4)#1 89.5(2) O(3)-Co(2)-O(4) 85.49(15) O(3)#1-Co(2)-O(4) 94.92(15) O(4)-Co(2)-O(4)#1 symmetry code #1: -x + 3/4, -y + 3/4, z
2.124(5) 2.041(4) 2.079(4) 2.146(4) 2.101(4) 2.062(4) 94.51(17) 87.57(18) 88.77(17) 177.19(18) 175.3(2) 88.29(18) 88.43(18) 89.7(2) 91.12(16) 85.18(15) 170.66(15) 94.42(15) 94.92(15) 85.49(15) 179.4(2)
Ni(1)-N(1) Ni(1)-O(1) Ni(1)-O(2) Ni(2)-N(2) Ni(2)-O(3) NI(2)-O(4) N(1)-Ni(1)-N(1)#1 N(1)-Ni(1)-O(1)#1 N(1)-Ni(1)-O(2)#1 N(1)#1-Ni(1)-O(1)#1 N(1)#1-Ni(1)-O(2)#1 O(1)-Ni(1)-O(2) O(1)#1-Ni(1)-O(2) O(2)-Ni(1)-O(2)#1 N(2)-Ni(2)-O(3) N(2)-Ni(2)-O(4) N(2)#1-Ni(2)-O(3) N(2)#1-Ni(2)-O(4) O(3)-Ni(2)-O(3)#1 O(3)-Ni(2)-O(4)#1 O(3)#1-Ni(2)-O(4)#1
6 2.097(3) Ni(1)-N(1)#1 2.036(3) Ni(1)-O(1)#1 2.066(3) Ni(1)-O(2)#1 2.073(4) Ni(2)-N(2)#1 2.044(3) NI(2)-O(3)#1 2.023(3) Ni(2)-O(4)#1 90.82(18) N(1)-Ni(1)-O(1) 85.48(12) N(1)-Ni(1)-O(2) 172.95(12) N(1)#1-Ni(1)-O(1) 93.84(13) N(1)#1-Ni(1)-O(2) 91.34(13) O(1)-Ni(1)-O(1)#1 87.67(12) O(1)-Ni(1)-O(2)#1 93.03(12) O(1)#1-Ni(1)-O(2)#1 87.32(12) N(2)-Ni(2)-N(2)#1 87.67(14) N(2)-Ni(2)-O(3)#1 89.68(13) N(2)-Ni(2)-O(4)#1 178.77(14) N(2)#1-Ni(2)-O(3)#1 92.85(13) N(2)#1-Ni(2)-O(4)#1 91.2(2) O(3)-Ni(2)-O(4) 89.83(14) O(3)#1-Ni(2)-O(4) 87.59(14) O(4)-Ni(2)-O(4)#1 symmetry code #1: -x + 5/4, -y + 5/4, z
2.097(3) 2.036(3) 2.066(3) 2.073(4) 2.044(3) 2.023(3) 93.84(13) 91.34(13) 85.48(12) 172.95(12) 179.04(17) 93.03(12) 87.67(12) 93.47(19) 178.77(14) 92.85(13) 87.67(14) 89.68(13) 87.59(14) 89.83(14) 176.31(18)
(4pds)]2 ) [C40H20F24N4Ni2O8S4]: C, 34.66 (34.69); H, 1.45 (1.70); N, 4.04 (3.88). IR νKBr (cm-1): 3106w, 1645s, 1595s, 1552s, 1524s, 1482s, 1418s, 1257s, 1200s, 1146s, 795m, 715m, and 671m. X-ray Crystallography. X-ray diffraction data for single crystals were collected on a Bruker SMART APEX CCD diffractometer equipped with a graphite crystal and incident beam monochromator using Mo KR radiation (λ ) 0.71073 Å). Crystal data, data collection parameters, and analysis statistics for 2-6 are listed in Table 1. Selected bond lengths and angles are given in Tables 2 and 3. The frames were integrated in the Siemens SAINTPLUS software package,27 and the data were corrected for absorption using the SADABS program.28 The structures were solved by the direct method (SHELXS 9729) and expanded using Fourier techniques. The nonhydrogen atoms were refined anisotropically. The hydrogen atoms attached to carbon atoms were inserted at the calculated positions and allowed to ride on their respective parent atoms. The hydrogen atoms attached to oxygen atoms were not located. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Center as supplementary publication nos. CCDC 223062 (2), CCDC 223060 (3), CCDC 223061 (4), CCDC 226171 (5), and CCDC 227461 (6). Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, United Kingdom [Fax: (+44)1223-336-033. E-mail:
[email protected]].
Table 4. Correlation between Structures and Reaction Solvents in Complexes of 4pds with M(hfac)2 metals
MeOH
CHCl3
CCl4
Mn(hfac)2 Cu(hfac)2 Co(hfac)2 Ni(hfac)2
zigzag chaina helical chaina b b
zigzag chain helical chain macrocycle macrocycle
helical chainc helical chainc macrocycle macrocycle
a Ref 19. b Powder X-ray diffraction patterns were diffused (amorphous). c After recrystallization from methanol.
Results and Discussion Synthesis, Structures, and Supramolecular Isomerism of 4pds Complexes with M(hfac)2. To investigate the basic features of the assembly modes of 4pds and M(hfac)2, we evaluated the dependence of the assembled structures on the metal species (M ) Mn, Cu, Co, and Ni) and the reaction solvents. The results are summarized in Table 4. Interestingly, the combination of variables was found to selectively generate coordination polymers [M(hfac)2(4pds)]n for M ) Mn and Cu and discrete metallamacrocycles [M(hfac)2(4pds)]2 for M ) Co and Ni, as shown in Scheme 2. In our previous work, we found that Mn(hfac)2 and Cu(hfac)2 afford zigzag and helical coordination polymers, respectively, when recrystallized from methanol.19 The configuration
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Scheme 2. Assembled Structures of 4pds Complexes with M(hfac)2
of the M(hfac)2 in these complexes coincides with those of the starting materials, Mn(hfac)2‚2H2O and Cu(hfac)2‚H2O, which are reported to have the trans and cis configurations, respectively.30,31 In the present study, we also used chloroform and tetrachloromethane as reaction solvents. It is noteworthy that although the structures of the M(hfac)2 coordination polymers with M ) Cu, Co, and Ni were independent of the reaction solvent, the structure of the Mn(hfac)2 coordination polymer was dependent on the reaction solvent; a zigzag chain compound zigzag[Mn(hfac)2(4pds)]n (1)19 was obtained from both methanol and chloroform, and a helical chain compound, helix-[Mn(hfac)2(4pds)]n (2), was obtained from tetrachloromethane. The latter complex was found to be isomorphous to [Cu(hfac)2(4pds)]n.19 In this system, therefore, changing the reaction solvent was found to induce “supramolecular isomerism”.5 Structural differences in 1 and 2 arise from both the configuration of Mn(hfac)2 and the chirality of the ligands: (i) Mn(hfac)2 adopts the trans and cis configurations in 1 and 2, respectively, and (ii) the chain in 1 is achiral, being composed of the alternate linking of both enantiomers of 4pds (-P-M-P-M-),16 but the chain in 2 is chiral, being composed of only one enantiomer (-P-P-P- or -M-M-M-). The crystal structure of 2 with the numbering scheme is shown in Figure 1. Although 2 is isomorphous with [Cu(hfac)2(4pds)]n, there is a slight difference in the coordination environments around the metal ions, as the Cu complex is highly distorted due to the Jahn-Teller effect.16 Consistent with this, the IR spectrum of [Cu(hfac)2(4pds)]n displays a CdO stretching band with two peaks at 1650 and 1669 cm-1,19 while 2 shows a single CdO band at 1653 cm-1. The IR spectra for 1 and 2 were almost identical, but a slight difference in crystal densities was found as follows: 1.733 and 1.720 g cm-3 for 1 and 2, respectively. This implies that the zigzag form 1 is somewhat more thermodynamically stable than the helix form 2. However, we are uncertain as to the factors responsible for
Figure 1. ORTEP drawing of the helical chain structure in 2. The hydrogen atoms are omitted for clarity.
the structural selectivity. It is to be noted that the intermediate reaction product from tetrachloromethane was amorphous, as revealed by powder X-ray diffraction measurements, and single crystals of 2 were grown by recrystallization of the product from methanol. Therefore, the structural dependence may correlate with the polarity of the reaction solvents, and possibly, the stability of the cis form of Mn(hfac)2 in tetrachloromethane, with retention of the configuration during recrystallization, may be essential for the phenomenon. On the other hand, M(hfac)2 (M ) Co, Ni) afforded 2:2 M:L metallamacrocyclic complexes, regardless of the reaction conditions. The solvent dependence of the structures of these macrocycles will be discussed in the next section. Structures of Metallamacrocyclic Complexes 3-6. Metallamacrocyclic complexes [M(hfac)2(4pds)]2‚4CHCl3 (M ) Co 3; M ) Ni 4) were obtained from chloroform, while [M(hfac)2(4pds)]2‚H2O (M ) Co 5; M ) Ni 6) complexes were obtained from tetrachloromethane. The metallamacrocycles are composed of two M(hfac)2 units with the cis configuration and two ligands with the same chirality. Thus, the macrocyclic units are chiral, although the bulk crystals are achiral because of the centrosymmetric space group. The macrocyclic structure of [Co(hfac)2(4pds)]2‚4CHCl3 (3) is shown in Figure 2. The nickel analogue 4 is isomorphous to 3. The coordination geometry of the metal ions is pseudo-octahedral, where the two hfac ligands occupy the cis positions and the 4pds ligands
Complexes from 4,4′-Dipyridyl Disulfide and M(hfac)2
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Table 5. Dimensions of the Macrocyclic Cavities in 1-6 and Relevant Complexes
a
compound
A: M‚‚‚M distance (Å)
B: (S-S)‚‚‚(S-S) distance (Å)
A×B (Å2)
3 4 5 6 [Ir2(H)4(PPh3)4(4pds)2]-(BF4)2‚3CH2Cl2‚H2Oa [(Et3P)4Pt2(4pds)2](NO3)4b
10.8 10.8 10.2 10.1 10.7 11.0
9.3 9.3 9.9 9.8 9.5 8.7
100.4 100.4 101.0 99.0 101.7 95.7
Ref 25. b Ref 24.
Figure 2. ORTEP drawing of 3 with atomic numbering schemes. The hydrogen atoms are omitted for clarity.
are bound to the remaining sites. In this chiral macrocyclic unit, a 2-fold axis lies through the centers of the S-S bonds. Complex 3 contains four chloroform molecules, two of which fit above and below the macrocyclic cavity as shown in Figure 2, while the others are located outside the macrocycle. The coordination geometries around the metal ions are usual for those found in N-donor coordinated M(hfac)2 complexes,19,32-34 and infrared spectra of compounds 3 and 4 exhibit CdO stretching bands at ca. 1639 and 1645 cm-1, respectively. The crystal structure of [Co(hfac)2(4pds)]2‚H2O (5) is shown in Figure 3. The nickel analogue 6 is isomorphous to 5. These complexes contain water molecules in the unit cell. The structures of these macrocycles are similar to those of 3 and 4, and the unit also has a 2-fold axis, but it lies through the two metal centers. The coordination geometry around the metal ions is normal. The infrared spectra of compounds 5 and 6 exhibit characteristic CdO stretching bands at ca. 1640 cm-1. In these complexes, the trifluoromethane moieties of adjacent molecules are located above and below the macrocycle and are accommodated by the cavity. It is noteworthy that the shape of the macrocycle is almost the same throughout 3-6 but varies slightly depending on the moieties that are accommodated in the cavity. The dimensions of the internal cavities of 3-6 and relevant complexes are listed in Table 5. Similar types of 2:2 M:L macrocyclic rings are also found
Figure 3. ORTEP view of adjacent two macrocycles in 5. The hydrogen atoms are omitted for clarity. Atomic numbering schemes around the metal ions in 5 and 6 are also shown. Table 6. C-S-S-C Torsion Angles (°) of 4pds in 1-6 and Relevant Complexes compound
torsion angle (°)
1 2 3 4 5 6 [Cu(hfac)2(4pds)]na [Ir2(H)4(PPh3)4(4pds)2](BF4)2‚3CH2Cl2‚H2Ob [(Et3P)4Pt2(4pds)2](NO3)4c
91.6(6) 90.0(1) 90.8(3), 89.1(3) 91.3(3), 89.5(3) 78.5(2) 78.0(2) 88.1(2) 87.2(2) 91.6
a
Ref 19. b Ref 25. c Ref 24.
in [Ir2(H)4(PPh3)4(4pds)2](BF4)2‚3CH2Cl2‚H2O22 and [(Et3P)4Pt2(4pds)2](NO3)4.24 The chirality of the former complex is the same as the present case, but the latter complex has an achiral unit composed of two enantiomers of 4pds. These examples demonstrate that the 2:2 M:L ring can have both chiral and achiral structures. In the present complexes, the sizes of the rectangular cavities are 9.3 Å (S‚‚‚S distance) by 10.8 Å (M‚‚‚M distance) for 3 and 4, and ca. 9.8 Å by ca. 10.2 Å for 5 and 6. Therefore, the cavities in the latter complexes are closer to square. To see the origin of the differences, the C-S-S-C torsion angles in 4pds in 1-6 and relevant complexes are compared in Table 6. It was found that 4pds is a rather rigid ligand that maintains the 90° bent angle, but 5 and 6 are exceptions, exhibit-
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Crystal Growth & Design, Vol. 5, No. 1, 2005
ing significantly smaller angles of 78°. This is because of the narrower space needed for the accommodation of the trifluoromethyl group, as compared with guests such as chloroform in the others, and this smaller angle leads to the expansion and reduction of the S‚‚‚S and the M‚‚‚M distances, respectively. Thus, the C-S-S-C bond can act as a hinge, and the cavity can change its shape just by torsion. Among the complexes in Table 5, deviation from square is remarkable in [(Et3P)4Pt2(4pds)2](NO3)4,24 which probably occurs because the complex only has an achiral unit and is thus exceptional. Thermal Properties of Metallamacrocyclic Complexes 3-6. Complexes 3 and 4 easily release the guest molecules at room temperature, and after they dry, the solids become insoluble in the usual organic solvents and only slightly soluble in DMF, whereas 3 and 4 themselves are soluble in common organic solvents such as chloroform. The dried samples also lost their crystallinity, as revealed by powder X-ray diffraction experiments. Therefore, the escape of the solvent molecules is probably accompanied by the deformation and entangling of the macrocyclic structure, which is presumably the cause of the decreased solubility. On the other hand, compounds 5 and 6 are more stable under air and soluble in common organic solvents such as diethyl ether, benzene, chlorobenzene, hot tetrachloromethane, and DMF. Thus, recrystallization of these compounds from different solvents was possible; we obtained orange microcrystalline solids of [Co(hfac)2(4pds)]2‚H2O‚CCl4 (5‚CCl4) from tetrachloromethane and [Co(hfac)2(4pds)]2‚H2O‚C6H5Cl (5‚C6H5Cl) from chlorobenzene and performed TG analysis to investigate guest release upon heating. Unfortunately, we failed to obtain satisfactory crystallographic data for these complexes. The TG curve of 5‚CCl4, shown in Figure 4a, shows a single weight loss between 100 and 167 °C of 10.2% of the original weight, corresponding to the loss of a water molecule and tetrachloromethane molecule (calculated 11.0%). The TG curve of 5‚C6H5Cl is shown in Figure 4b, which displays the losses of a water molecule between 98 and 118 °C (2.0% weight loss observed; 1.2% calculated) and a chlorobenzene molecule between 120 and 180 °C (7.1% weight loss observed; 7.5% calculated). In both complexes, the TG traces decreased abruptly around 200 °C and above, corresponding to sublimation. TG analysis of 5 also showed a weight loss between 250 and 300 °C due to sublimation, as shown in Figure 4c. We confirmed that TG traces of the raw materials, 4pds and Co(hfac)2‚2H2O, also showed sublimation at around 180 and 140 °C, respectively. Therefore, the macrocycles were shown to sublime at higher temperatures than the starting materials. For comparison purposes, TG analysis of the dried sample of 3 was performed, as shown in Figure 4d. The material was also found to exhibit sublimation in the temperature range of 270-320 °C, which is significantly higher than that of 5. This indicates that the simple macrocyclic structure is not maintained after drying, being consistent with the lower solubility of these materials in organic solvents. Conclusion We have systematically synthesized and structurally characterized supramolecules from M(hfac)2 and 4pds. Among the various possible structures emerging from the combination of cis/trans isomers of M(hfac)2 and P/M
Horikoshi et al.
Figure 4. TG curves for (a) 5‚CCl4, (b) 5‚C6H5Cl, (c) 5 (dried sample), and (d) 3 (dried sample).
enantiomers of 4pds, simple periodic structures with a minimum of crystallographically independent units have been isolated. Several different architectures were found under the topological limitations; the metal and solvent dependence of their supramolecular structures as well as a phenomenon of supramolecular isomerism have been found and discussed here. The results show that coordination polymers are formed for both the cis and the trans forms of M(hfac)2, but macrocycles are of the cis form only. This is a reasonable consequence because a macrocyclic structure for trans-M(hfac)2 would contain a 4:4 M:L ratio and is therefore not realistic. A question remains as to why no macrocycles have been formed for the cis forms of M(hfac)2 with M ) Mn and Cu, in contrast to the case of M ) Co and Ni, despite their geometrical similarity. It is to be noted that in the case of 4pds complexes, the ligand chirality is independent of supramolecular topology, because both chiral and achiral combinations of the ligands can produce similar supramolecular structures. The chirality of the constituents is interesting from the viewpoint of asymmetric crystal engineering, but chiral crystals have not been isolated so far in the metal complexes of 4pds. The introduction of chiral guests may be interesting to achieve chiral resolution. Acknowledgment. This work was performed using facilities of the Institute for Solid State Physics, the University of Tokyo. We thank Prof. T. Kitazawa (Toho
Complexes from 4,4′-Dipyridyl Disulfide and M(hfac)2
University) for his help with TG measurements. We also thank Prof. T. Sugawara and Dr. M. M. Matsushita (The University of Tokyo) for their help with X-ray measurements. We are indebted to Dr. K. Yoza [Bruker AXS (K.K.)] for his help with X-ray analysis. We acknowledge H. Yoshioka and H. Yamada (Kwansei Gakuin University) for their help with powder X-ray analysis. Supporting Information Available: X-ray crystallographic information files (CIF) and tables with X-ray structural information for 2-6. This material is available free of charge via the Internet at http://pubs.acs.org.
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