- Email: [email protected]
Synthesis, structures, and magnetic properties of one-dimensional Fe–M (M = NiII, CuII) coordination polymers bridged by nitroprusside
Inorganica Chimica Acta 360 (2007) 2523–2531 www.elsevier.com/locate/ica
Synthesis, structures, and magnetic properties of one-dimensional Fe–M (M = NiII, CuII) coordination polymers bridged by nitroprusside Young Sin You a, Jung Hee Yoon a, Jeong Hak Lim a, Hyoung Chan Kim b, Chang Seop Hong a,* a
Department of Chemistry and Center for Electro- and Photo-Responsive Molecules, Korea University, Seoul 136-701, Republic of Korea b Systems Research Team, Research and Development Division, Nuclear Fusion Research Center, Daejeon 305-333, Republic of Korea Received 21 September 2006; received in revised form 2 December 2006; accepted 8 December 2006 Available online 20 December 2006
Abstract Self-assembling [Fe(CN)5(NO)]2 and [M(L)]2+ (M = Ni, Cu; L = macrocycles) led to one-dimensional coordination polymers, [Ni(L1)][Fe(CN)5(NO)] Æ 2H2O (1) with parallel chains and [Cu(L2)][Fe(CN)5(NO)] Æ 3H2O (2) exhibiting a slanted chain structure. Compound 1 contains a planar macrocycle L1 coordinated to a slightly distorted octahedral Ni(II) ion in which the planarity of L1 gives rise to piling up chains in parallel. In contrast, a more flexible macrocyclic ligand L2 in 2 that surrounds a Cu center with a tetragonal elongation has bulky cyclohexyl groups together with pendant methyl side groups. The presence of the methyl groups on L2 in a chain makes the cyclohexyl groups in an adjacent chain tilted against the CuN4 basal plane with the methyl groups, eventually resulting in the slanted chain structure. Magnetic data demonstrate that antiferromagnetic interactions (J 0.13 cm1) are operating although the paramagnetic centers are linked by the long diamagnetic [Fe(CN)5(NO)]2 anion. 2006 Elsevier B.V. All rights reserved. Keywords: Nitroprusside; Coordination polymers; Crystal structures; Magnetic properties
1. Introduction Coordination polymers have been one of the active subjects because of emergent fascinating properties found in molecule-based magnetic materials with high TC [1], photo-induced magnetism [2], and magnetochiral effect [3], molecular nanomagnetism [4], and metal–organic frameworks [5] functioning for storage, exchange, and separation. To achieve such functional coordination materials cyanide-based complexes as bridges to link metal centers have been frequently used, in turn producing fruitful results exhibiting intriguing characters [6,7]. In the construction of magnetic bimetallic systems, the nitroprusside anion [Fe(CN)5(NO)]2 has not been explored extensively compared with other hexacyanometalates [M(CN)6]n (M = FeII/III, CrIII), because the precur*
Corresponding author. E-mail address: [email protected] (C.S. Hong).
0020-1693/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.12.023
sor is diamagnetic [8]. However, the use of the photochromic nitroprusside provided novel photomagnetic materials controlled by light irradiation as exemplified in Ni[Fe(CN)5(NO)] Æ 5.3H2O [9]. Moreover, the study on bimetallic coordination compounds bridged by nitroprusside is still an appealing theme because the nitroprusside bridge can serve as a good building block for multi-dimensional structures. Only a few examples were reported to date with diverse structures ranging from dinuclear molecules [10,11], one-dimensional chains [10,12], to twodimensional networks [10,13]. Since most of them have open polydentate coligands of diamines and triamines, chemical design of specific coordination environments for preprogrammed structures is promptly hampered by more than two binding sites for incoming donor atoms of bridging ligands, and therefore suitable systems aiming to tuning molecular structures merit to be sought. To fabricate tailor-made molecular architectures continual pursuits are to find a rational synthetic route that
2524
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
provides a clue to control overall structural patterns [14,15]. To this end, tetradentate macrocycles whose four nitrogens can coordinate the equatorial positions of an octahedral metal center are one of the proper coligands because the remaining two apical sites are solely available for coordination to bridging ligands and then contacts between molecules are readily influenced by the presence of side groups on the ligands [16]. Hence fine-tuning of molecular structures would result if one employs the macrocyclic ligands with various bulky side groups. Thus, the successful design of coordination compounds with desired structures would be one of the current issues to establish structure–property relationship on coordination materials.
N
HN
NH HN
N
NH HN
NH
L1
L2
Herein we report the syntheses, crystal structures, and magnetic properties of two one-dimensional coordination polymers, [Ni(L1)][Fe(CN)5(NO)] Æ 2H2O (1) and [Cu(L2)][Fe(CN)5(NO)] Æ 3H2O (2), chelated with tetradentate macrocyclic ligands. The molecular structure of compound 1 with a planar macrocyclic ligand L1 is extended by packing chains in parallel while, remarkably, chains in 2 are slanted to each other because of the steric effect of bulky cyclohexyl and methyl side groups on L2. Magnetic data show that the long diamagnetic nitroprusside spacer mediates weak antiferromagnetic interactions between paramagnetic metal centers.
in the dark gave pale yellow crystals in a yield of 55%. Anal. Calc. for C17H28FeN10NiO3: C, 38.2; H, 5.27; N, 26.2. Found: C, 38.0; H, 5.43; N, 26.5%. Selected IR data (KBr pellet): mCN = 2179, 2158, 2145, 2137 cm1, mNO = 1917 cm1. 2.1.3. Synthesis of [Cu(L2)][Fe(CN)5(NO)] Æ 3H2O (2) A DMF solution of [Cu(L2)](ClO4)2 (0.15 mmol) was added to Na2[Fe(CN)5(NO)] Æ 2H2O (0.15 mmol) dissolved in water. After stirring for a few minutes, the resulting solution was filtered. The filtrate was allowed to stand undisturbed in the dark, giving violet crystals in a yield of 68%. Anal. Calc. for C25H46CuFeN10O4: C, 44.8; H, 6.92; N, 20.9. Found: C, 44.7; H, 6.90; N, 20.6%. Selected IR data (KBr pellet): mCN = 2154, 2139 cm1, mNO = 1909 cm1. 2.2. Physical measurements Elemental analyses for C, H, and N were performed at the Elemental Analysis Service Center of Sogang University. Infrared spectra were obtained from KBr pellets with a Bomen MB-104 spectrometer. Magnetic susceptibilities for 1 and 2 were carried out using a Quantum Design MPMS-7 SQUID magnetometer. The susceptibility data were corrected for the sample holder and diamagnetic contributions from the samples using Pascal’s constants. 2.3. Crystallographic structure determination X-ray data for 1 and 2 were collected on a Bruker SMART APEXII diffractometer equipped with graphite ˚ ). The monochromated Mo Ka radiation (k = 0.71073 A reflection data were corrected for Lorentz and polarization factors. The structures were solved by direct methods and refined by full-matrix least-squares analysis using anisotropic thermal parameters for nonhydrogen atoms with
2. Experimental
Table 1 Crystal data and structure refinement for 1 and 2
2.1. Preparations
Compound
2.1.1. Materials [Ni(L1)](ClO4)2 [17] and [Cu(L2)](ClO4)2 [18] were prepared according to the literature methods. All of the other chemicals and solvents are commercially available and used as received. All manipulations were performed under aerobic conditions. Caution: Perchlorate salts of metal compounds with organic ligands are potentially explosive. Only small amounts of material should be cautiously handled. 2.1.2. Synthesis of [Ni(L1)][Fe(CN)5(NO)] Æ 2H2O (1) A DMF solution of [Ni(L1)](ClO4)2 (0.2 mmol) was treated with Na2[Fe(CN)5(NO)] Æ 2H2O (0.20 mmol) dissolved in water. The resultant mixture was stirred for 10 min and filtered. The slow evaporation of the solution
1
Empirical formula C17H28FeN10NiO3 Formula weight 535.05 Crystal system monoclinic Space group P21/n ˚) a (A 11.4040(2) ˚) b (A 14.3070(3) ˚) c (A 14.9021(3) b () 100.3570(10) ˚ 3) V (A 2391.77(8) Z 4 l (mm1) 1.433 1.486 q (g cm3) F(0 0 0) 1112 Goodness-of-fit 1.059 R1a [I > 2r(I)] 0.0570 wR2b [I > 2r(I)] 0.1353 P P a R1 = iFoj jFci/ jFcj. P P b wR2 ¼ ½ wðF 2o F 2c Þ2 = wðF 2o Þ2 1=2 .
2 C25H46CuFeN10O4 670.11 monoclinic Cc 19.0742(5) 8.5204(3) 18.8634(6) 101.3840(10) 3005.36(16) 4 1.239 1.481 1412 1.079 0.0233 0.0642
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
the SHELXTL program [19]. All hydrogen atoms except for hydrogens bound to water molecules were calculated at idealized positions and refined with the riding models. Crystallographic data and the details of data collection are listed in Table 1. 3. Results and discussion 3.1. Synthesis and characterization The title compounds were prepared by a reaction mixture of the [Fe(CN)5(NO)]2 dianion and [M(L)](ClO4)2 (M = Ni, Cu; L = L1, L2) where the reaction progress was readily checked by the absence of the IR peaks characteristic of ClO4 anion of the M precursor. The distinct IR absorption bands in the range 2200–1900 cm1 concern CN and linear NO+ stretchings. The CN vibrations are observed at 2179, 2158, 2145, 2137 cm1 for 1 and 2154, 2139 cm1 for 2, respectively, which are in good agreement with other compounds containing nitroprusside [10–13]. Single strong bands centered at 1917 cm1 for 1 and 1909 cm1 for 2 can be attributed to the NO stretching frequency. The vibrations are situated lower than that observed for the nitroprusside anion (1939 cm1), which also coincides with nitroprusside-linked systems [10–13]. 3.2. Description of the structures 3.2.1. Complex 1 An ORTEP diagram of 1 is depicted in Fig. 1. Selected bond distances and angles are summarized in Table 2. The crystal structure of 1 is formed by nitroprusside anion and [Ni(L1)]2+ cation. The structural aspect around the Fe ion of nitroprusside can be described as a regular octahedron consisting of five CN groups with Fe–C distances spanning ˚ and one NO group with a Fe–N from 1.936 to 1.953 A ˚ , shorter than the Fe–C bond lengths. length of 1.662(4) A The Fe–CN and Fe–NO angles are almost linear, ranging from 172.8 to 179.4. These structural parameters are con-
Fig. 1. ORTEP diagram of 1 with the atom-labeling scheme. Symmetry code: (i) x + 1/2, y + 1/2, z 1/2.
2525
Table 2 ˚ ) and angles () for 1a Selected bond lengths (A Fe(1)–N(6) Fe(1)–C(1) Fe(1)–C(5) N(1)–Ni(1) Ni(1)–N(10) Ni(1)–N(9) N(6)–Fe(1)–C(2) C(2)–Fe(1)–C(1) C(2)–Fe(1)–C(4) N(6)–Fe(1)–C(5) C(1)–Fe(1)–C(5) N(6)–Fe(1)–C(3) C(1)–Fe(1)–C(3) C(5)–Fe(1)–C(3) C(1)–N(1)–Ni(1) N(3)–C(3)–Fe(1) C(4)i–N(4)–Ni(1) O(1)–N(6)–Fe(1) N(10)–Ni(1)–N(9) N(10)–Ni(1)–N(7) N(9)–Ni(1)–N(7) N(8)–Ni(1)–N(1) N(7)–Ni(1)–N(1) N(8)–Ni(1)–N(4) N(7)–Ni(1)–N(4) C(6)–N(7)–Ni(1) C(9)–N(8)–Ni(1) C(12)–N(9)–Ni(1) C(15)–N(10)–Ni(1)
1.662(4) 1.937(4) 1.946(5) 2.090(3) 1.998(5) 2.022(4) 94.92(18) 89.51(16) 88.05(16) 95.44(17) 89.24(16) 178.83(16) 85.41(16) 85.38(17) 161.2(3) 179.4(4) 161.4(3) 177.3(3) 85.9(2) 93.4(2) 176.75(15) 88.17(15) 88.53(14) 90.37(15) 91.13(14) 107.0(3) 145.6(7) 108.0(3) 147.0(7)
Fe(1)–C(2) Fe(1)–C(4) Fe(1)–C(3) N(4)i–Ni(1) Ni(1)–N(8) Ni(1)–N(7) N(6)–Fe(1)–C(1) N(6)–Fe(1)–C(4) C(1)–Fe(1)–C(4) C(2)–Fe(1)–C(5) C(4)–Fe(1)–C(5) C(2)–Fe(1)–C(3) C(4)–Fe(1)–C(3) N(1)–C(1)–Fe(1) N(2)–C(2)–Fe(1) N(4)ii–C(4)–Fe(1) N(5)–C(5)–Fe(1) N(10)–Ni(1)–N(8) N(8)–Ni(1)–N(9) N(8)–Ni(1)–N(7) N(10)–Ni(1)–N(1) N(9)–Ni(1)–N(1) N(10)–Ni(1)–N(4) N(9)–Ni(1)–N(4) N(1)–Ni(1)–N(4) C(17)–N(7)–Ni(1) C(7)–N(8)–Ni(1) C(11)–N(9)–Ni(1) C(13)–N(10)–Ni(1)
1.936(4) 1.942(4) 1.953(4) 2.130(3) 2.003(5) 2.033(4) 95.42(16) 92.69(16) 171.71(17) 169.64(17) 91.73(16) 84.27(18) 86.46(16) 179.2(4) 179.5(4) 172.8(4) 178.7(4) 178.47(18) 94.5(2) 86.3(2) 93.33(15) 88.36(14) 88.14(15) 92.01(14) 178.51(13) 108.7(3) 108.3(4) 109.9(3) 109.1(4)
a Symmetry transformations used to generate equivalent atoms: (i) x + 1/2, y + 1/2, z 1/2; (ii) x 1/2, y + 1/2, z + 1/2.
sistent with those reported for bimetallic compounds with [Fe(CN)5(NO)]2 anion [10–13]. The Ni atom adopts a distorted octahedral geometry composed of four equatorial ˚ ) and two axial N N atoms from L1 (av Ni–N = 2.01(2) A atoms from bridging CN ligands (Ni1–N1 = 2.090(3), ˚ ; i = 0.5 + x, 0.5 y, 0.5 + z). Ni1–N4i = 2.123(3) A The equatorial NiN4 plane is virtually planar with the larg˚ at est deviation from the least-squares plane of 0.0412 A N10. The presence of sp2 carbons (C9 and C15) and nitrogens (N8 and N10) on L1 establishes planarity with linked neighboring atoms, while the other carbon atoms (C6, C11, ˚ C12, C17) on L1 lie with a mean deviation of 0.57(3) A from the basal plane toward N4i. The bridging cyanides axially coordinate to the Ni center, forming a small bent angle of Ni–NC = 161.3(1). The nearly planar structure of L1 is not prone to cause a steric effect toward [Fe(CN)5(NO)]2 unit, which is responsible for such a bending of the Ni–NC angle. The coordination chains of 1, constructed by self-assembling the nitroprusside and Ni precursor, are well packed in a three-dimensional pattern as seen in Fig. 2. The position of the NO groups on nitroprussides is varied alternately along the chain. The shortest intrachain distance is ˚ for Fe–Ni and 10.165 A ˚ for Ni–Ni. In Fig. 2a, 5.099 A the shortest contact between chains is found to be ˚ between N9 on L1 and N5 on CN group, which 3.086 A is smaller than the sum of the van der Waals radii
2526
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
Fig. 2. Extended molecular view of 1 displaying packing feature of chains in the bc-plane (a) and ac-plane (b). The representative shortest contacts between chains are indicated as dotted lines. Colors denote Fe in pink, Ni in green, N in blue, O in red, and C in grey. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
˚ ). The shortest interchain M–M distances are (3.10 A ˚ for Ni–Ni, 8.013 A ˚ for Fe–Ni, and 9.059 A ˚ for 8.270 A Fe–Fe. In comparison, Fig. 2b reveals that the closest sep˚ between C8 aration between chains corresponds to 3.365 A on L1 and O1 on NO group, which is a little longer than ˚ ). The shortest the sum of the van der Waals radii (3.22 A ˚ for Ni–Ni, 8.665 A ˚ interchain M–M distances are 8.531 A ˚ for Fe–Fe. The observation of for Fe–Ni, and 8.574 A the shorter distance for Fe–Ni in Fig. 2a compared with that in Fig. 2b could be pertinent to some kind of interchain interactions occurring between N9 and N5. A number of hydrogen bonds are formed among lattice water molecules, CN, and NO groups. Thus, the inclusion of the planar macrocycle L1 into coordination polymers helps to construct parallel chains by stacking them regularly in this system. 3.2.2. Complex 2 An ORTEP diagram of 2 is displayed in Fig. 3. Selected bond distances and angles are tabulated in Table 3. The structural parameters in an octahedral Fe center ˚ and exhibit an average Fe–C bond length of 1.940(6) A
Fig. 3. Molecular views of (a) the asymmetric unit with the atom-labeling scheme and (b) showing a one-dimensional chain structure of 2. Symmetry code: (i) x + 1/2, y 1/2, z. Colors represent Fe in pink, Cu in brown, N in blue, O in red, and C in grey. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
˚ , which are quite similar to those Fe–N of 1.6585(16) A of 1. The Fe–C(N)–N(O) angles in the range 174.48– 179.35 are close to linearity. The Cu ion resides in a distorted octahedral arrangement, occupied by four equato˚ ) and two rial N atoms from L2 (av Cu–N = 2.04(2) A apical N atoms from bridging CN groups (Cu1– ˚ , Cu1–N2i = 2.5638(17) A ˚ ; i = 0.5 x, N1 = 2.4458(16) A 0.5 + y, z). The tetragonally elongated environment around the Cu center is definitely associated with the Jahn–Teller effect of an octahedral Cu(II) ion. A noticeable structural feature is that the methyl side groups of the macrocycle L2 stand virtually upright with respect to the CuN4 basal plane (Fig. 3b), functioning as a steric object. In fact, the bond angle of Cu–NC (cyanide) remains substantially bent, being 139.96(14) for Cu1– N1–C1, which is quite smaller than the corresponding Ni–NC angle of 161.3(1) for 1. It is also worthy of noting that unlike L1, L2 includes two bulky cyclohexyl groups, which would critically affect the overall structural patterns. The NO groups are on the same side in a chain ˚ for Fe– and the shortest intrachain distances are 5.176 A ˚ Cu and 10.445 A for Cu–Cu. Fig. 4 shows a three-dimensional packing diagram in which two kinds of chains, indicated by blue and orange
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531 Table 3 ˚ ) and angles () for 2a Selected bond lengths (A Fe(1)–N(6) Fe(1)–C(2) Fe(1)–C(3) N(1)–Cu(1) Cu(1)–N(8) Cu(1)–N(9) N(6)–Fe(1)–C(1) C(1)–Fe(1)–C(2) C(1)–Fe(1)–C(5) N(6)–Fe(1)–C(3) C(2)–Fe(1)–C(3) N(6)–Fe(1)–C(4) C(2)–Fe(1)–C(4) C(3)–Fe(1)–C(4) C(1)–N(1)–Cu(1) N(3)–C(3)–Fe(1) N(5)–C(5)–Fe(1) N(8)–Cu(1)–N(10) N(10)–Cu(1)–N(9) N(10)–Cu(1)–N(7) N(8)–Cu(1)–N(1) N(9)–Cu(1)–N(1) C(6)–N(7)–Cu(1) C(12)–N(8)–Cu(1) C(16)–N(9)–Cu(1) C(22)–N(10)–Cu(1)
1.6585(16) 1.9382(18) 1.944(2) 2.4458(16) 2.0213(15) 2.0591(14) 94.98(8) 170.34(8) 90.70(7) 96.32(8) 90.34(7) 178.69(9) 85.24(8) 84.99(8) 139.96(14) 179.21(17) 178.00(17) 179.25(8) 85.01(6) 94.75(6) 89.53(6) 85.19(6) 107.75(11) 114.77(11) 107.93(11) 114.24(11)
Fe(1)–C(1) Fe(1)–C(5) Fe(1)–C(4) Cu(1)–N2i Cu(1)–N(10) Cu(1)–N(7) N(6)–Fe(1)–C(2) N(6)–Fe(1)–C(5) C(2)–Fe(1)–C(5) C(1)–Fe(1)–C(3) C(5)–Fe(1)–C(3) C(1)–Fe(1)–C(4) C(5)–Fe(1)–C(4) N(1)–C(1)–Fe(1) N(2)–C(2)–Fe(1) N(4)–C(4)–Fe(1) O(1)–N(6)–Fe(1) N(8)–Cu(1)–N(9) N(8)–Cu(1)–N(7) N(9)–Cu(1)–N(7) N(10)–Cu(1)–N(1) N(7)–Cu(1)–N(1) C(24)–N(7)–Cu(1) C(11)–N(8)–Cu(1) C(14)–N(9)–Cu(1) C(21)–N(10)–Cu(1)
1.9305(18) 1.9400(19) 1.9457(19) 2.5638(17) 2.0272(15) 2.0627(15) 94.62(8) 93.47(8) 87.63(8) 89.69(7) 170.13(8) 85.15(8) 85.22(8) 177.55(16) 174.48(16) 179.35(18) 177.50(16) 95.20(6) 85.03(6) 178.71(7) 91.20(6) 96.08(6) 121.73(11) 108.39(11) 121.55(11) 107.58(11)
a Symmetry transformations used to generate equivalent atoms: (i) x + 1/2, y 1/2, z.
2527
˚ , N5– propyl backbones on L2 (N3–C23 = 3.395 A ˚ C13 = 3.372 A). The shortest interchain M–M separations ˚ for Fe–Fe and Cu–Cu, 7.826 A ˚ for Fe–Cu. On are 8.520 A the other hand, the respective cyclohexyl groups from orange and blue chains become close as given in Fig. 5b, strikingly leading to the formation of such slanted chains. At contact points of the two chains the shortest distances among cyanides, cyclohexyl, and methyl groups are ˚ for C15–C10, 3.463 A ˚ for N3–C8, 3.569 A ˚ for 4.098 A ˚ N5–C18, and 4.034 A for C25–C20, respectively. The most important factor to govern the observed tilted structure is likely the interchain interactions between the methyl and cyclohexyl groups where a methyl moiety on one orange chain can push away a cyclohexyl unit on the other blue chain and render the ring of the corresponding group slanted with respect to the CuN4 basal plane on the orange chain. The shortest interchain separations between metal ions on the blue and orange chains, respectively, are rather ˚ for Fe–Fe, 9.801 A ˚ for Fe–Cu, longer, being 9.435 A 10.316 for Cu–Cu, which result from the orientation of the bulky cyclohexyl groups between the chains. Consequently, it is manifest that the protruded side groups of the macrocyclic ligand L2 play a pivotal role in attaining the atypical structural type in this system. Many hydrogen bonds among lattice water molecules, CN, and NO groups are present in 2. 3.3. Magnetic properties
colors, are running in a tilted fashion. This structural peculiarity in 2 is wholly intriguing and obviously different from that of 1. As shown in Fig. 5a, the bulky cyclohexyl groups are positioned away from each other and do not participate in stacking the blue chains in a parallel manner. Thus, the close contacts are mainly achieved between cyanide and
For 1, the vmT value of 1.23 cm3 K mol1 at 300 K is close to the spin-only one (1.00 cm3 K mol1) expected for a noninteracting Ni(II) (S = 1) ion (Fig. 6). The [Fe(CN)5(NO)]2 anion is known to be diamagnetic because of the formation of an electron pair between
Fig. 4. Three-dimensional structure in the ab-plane of 2. The blue and orange chains are located tilted to each other. The lattice water molecules are indicated in red. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
2528
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
Fig. 5. Extended molecular structure of 2 illustrating (a) parallel stacked chains (blue) and (b) slanted chains (blue and orange) in the different layers. The closest contacts between adjacent chains are indicated as dotted lines. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
unpaired electrons of the low-spin Fe(III) and nitrosyl free radical [9–13]. As the temperature is lowered, vmT decreases slowly and below 40 K drops down to 0.477 cm3 K mol1 at 1.8 K.
Since the Ni(II) ion in 1 is in the axially distorted octahedral surrounding, the magnetic data can be fitted using the equation including zero-field splitting and ignoring intrachain interactions, defined as
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
vz ¼ ð2Ng2 b2 =kT Þ½expðD=kT Þ=ð1 þ 2 expðD=kT ÞÞ 2 2
vx ¼ ð2Ng b =DÞf½1 expðD=kT Þ=½1 þ 2 expðD=kT Þg vm ¼ ðvz þ 2vx Þ=3 ð1Þ where vz is the parallel magnetic susceptibility, vx the perpendicular magnetic susceptibility, and D the axial zero-field splitting parameter [20]. The best result gives g = 2.211 and D = 6.54 cm1, in accordance with the reported values [21]. But the high-temperature magnetic data were not well reproduced with this model. When temperature-independent paramagnetism (TIP) was included, the parameters are g = 2.21, D = 6.50 cm1, and TIP = 3.0 · 105 cm3 mol1, still giving a poor fit in the high-temperature region. This implies that intrachain magnetic contribution through the diamagnetic nitroprusside spacer could be taken into account. To quantify magnetic interactions along the chain, an analytical expression for S = 1 on the basis of the spin Hamiltonian H = JRiSAi Æ SAi+1 was employed in the temperature range of 20–300 K where the local anisotropy is neglected [22] vm ¼ ðNg2 b2 =kT Þ½ð1:0 þ 0:0194x þ 0:777x2 Þ =ð3:0 þ 4:346x þ 3:232x2 þ 5:834x3 Þ
ð2Þ
with x = jJj/kT. The fitting of the experimental data with Eq. (2) produces g = 2.21, J = 0.13 cm1, and TIP = 0. These magnetic data can also be treated by taking an infinite chain model of classical spins derived by Fisher [23] vm ¼ ½Ng2 b2 SðS þ 1Þ=kT ½ð1 þ uÞ=ð1 uÞ
ð3Þ
with u = coth[JS(S + 1)/kT] kT/[JS(S + 1)]. The fitting result corresponds to g = 2.21, J = 0.14 cm1, and TIP = 0. As shown in the inset of Fig. 6, the theoretical curves of the two magnetic chain models are actually superimposed and well reproduce the vmT product in the high temperature regime. Therefore, despite the long separa˚ ) via [Fe(CN)5(NO)]2 the very weak intrachain tion (>10 A
2529
antiferromagnetic interaction is operative, which is consistent with a one-dimensional Cu–Fe bimetallic system in which the paramagnetic Cu centers are bridged by the nitroprusside [12b]. This has been demonstrated on numerous occasions, for instance, in the case of antiferromagnetic or ferromagnetic interactions mediated by the diamagnetic NiðCNÞ4 2 or ferrocyanide bridges [24,25]. The obtained J value falls into the normal range of magnetic strength for nitroprusside or terephthalate-bridged complexes where ˚ the bridging ligands link two metal centers within 10–11 A [12b,26]. The field dependence of the magnetization for 1 was collected at 1.8 K in the field range 0–7 T (Fig. 7). The magnetization data are lower than the Brillouin curve deduced for an isolated Ni(II) spin with g = 2.21, demonstrating that at 1.8 K the weak antiferromagnetic couplings and zero-field splitting exist. The weak contributions are overcome by raising a magnetic field up to 7 T, eventually reaching a saturation value. For 2, the vmT value is equal to 0.42 cm3 K mol1 at 300 K, consistent with the spin-only one (0.375 cm3 K mol1) expected for an uncoupled Cu(II) ion (Fig. 8). The vmT on coupling goes on a slow decrease and then drops abruptly, arriving at 0.39 cm3 K mol1 at 1.8 K. The magnetic data can be interpreted with a numerical expression based on the spin Hamiltonian H = JRiSAi Æ SAi+1 [27] vm ¼ ðNg2 b2 =kT Þ½ð0:25 þ 0:074975x þ 0:075235x2 Þ =ð1:0 þ 0:9931x þ 0:172135x2 þ 0:757825x3 Þ
ð4Þ
with x = jJj/kT. The best fit yields g = 2.12(1) and J = 0.12(1) cm1, indicating the presence of weak antiferromagnetic interactions mediated by nitroprusside. The magnitude of magnetic exchange coupling in 2 is analogous to 1 and metal compounds bridged by nitroprusside or terephthalate [12b,26]. Such weak couplings are also confirmed by the M(H) data where the magnetization data in the low field regime are slightly lower than the Brillouin curve calculated from g = 2.12 and S = 1/2 (inset of Fig. 8).
1.2 2.0 -1
T (cm K mol )
1.0
1.22
1.5
m
M (N )
3
0.8
m
3
-1
T (cm K mol )
1.23
0.6
1.21 0
100
200
1.0
300
T (K)
0.5
0.4 0
50
100
150
200
250
300
T (K)
0.0 0
Fig. 6. Plot of vmT vs. T for 1. The inset is the blow-up of the vmT product. The theoretical fits are derived from an isolated Ni(II) model containing zero-field splitting with (dashed line) and without TIP (dotted line) and 1D Ni(II) chain models (solid line), respectively.
20000
40000
60000
80000
H (G)
Fig. 7. Field dependence of the magnetization for 1. The Brillouin curve for a noninteracting Ni(II) (S = 1) is drawn at 1.8 K.
2530
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
Basic Research Promotion Fund) (KRF-2005-070C00068) and CRM-KOSEF. We also thank an Operation Program on Shared Research Equipment of KBSI and MOST.
0.45
1.2
M (N )
-1
T (cm K mol )
0.40
m
3
0.35
0.30
0.8
References
0.4
[1] S.M. Holmes, G.S. Girolami, J. Am. Chem. Soc. 121 (1999) 5593. [2] A. Dei, Angew. Chem., Int. Ed. 44 (2005) 1160. [3] E.-Q. Gao, Y.-F. Yue, S.-Q. Bai, Z. He, C.-H. Yan, J. Am. Chem. Soc. 126 (2004) 1419. [4] D. Gatteschi, R. Sessoli, Angew. Chem., Int. Ed. 42 (2003) 268. [5] S.L. James, Chem. Soc. Rev. 32 (2003) 276. [6] (a) S.-i. Ohkoshi, H. Tokoro, T. Hozumi, Y. Zhang, K. Hashimoto, C. Mathonie´re, I. Bord, G. Rombaut, M. Verelst, C. Cartier dit Moulin, F. Villain, J. Am. Chem. Soc. 128 (2006) 270; (b) H. Imai, K. Inoue, K. Kikuchi, Y. Yoshida, M. Ito, T. Sunahara, S. Onaka, Angew. Chem., Int. Ed. 43 (2004) 5618. [7] S. Kitagawa, R. Kitaura, S.-i. Noro, Angew. Chem., Int. Ed. 43 (2004) 2334. [8] (a) M. Ohba, H. Okawa, N. Fukita, Y. Hashimoto, J. Am. Chem. Soc. 119 (1997) 1011; (b) H.-Z. Kou, S. Gao, O. Bai, Z.-M. Wang, Inorg. Chem. 40 (2001) 6287; (c) E. Colacio, M. Ghazi, H. Stoeckli-Evans, F. Lloret, J.M. Moreno, C. Pe´rez, Inorg. Chem. 40 (2001) 4876. [9] Z.-Z. Gu, O. Sato, T. Iyoda, K. Hashimoto, A. Fujishima, Chem. Mater. 9 (1997) 1092. [10] (a) M. Clemente-Leo´n, E. Coronado, J.R. Gala´n-Mascaro´s, C.J. Go´mez-Garcı´a, Th. Woike, J.M. Clemente-Juan, Inorg. Chem. 40 (2001) 87; (b) B. Bellouard, M. Clemente-Leo´n, E. Coronado, J.R. Gla´nMascaro´s, C. Gime´nez-Saiz, C.J. Go´mez-Garcı´a, Th. Woike, Polyhedron 20 (2001) 1615. [11] (a) H.L. Shyu, H.-H. Wei, J. Coord. Chem. 47 (1999) 319; (b) K.L. Zhang, Y. Xu, Z. Wang, C.M. Jin, X.Z. You, Trans. Met. Chem. 27 (2002) 95; (c) Z. Smekal, Z. Travnicek, J. Marek, M. Nadvornik, Aust. J. Chem. 53 (2000) 225. [12] (a) H.L. Shyu, H.H. Wei, Y. Wang, Inorg. Chim. Acta 258 (1997) 81; (b) H.Z. Kou, H.M. Wang, D.Z. Liao, P. Cheng, Z.H. Jiang, S.P. Yan, X.Y. Huang, G.L. Wang, Aust. J. Chem. 51 (1998) 661. [13] N. Shaikh, A. Panja, S. Goswami, P. Banerjee, M. Kubiak, Z. Ciunik, M. Puchalska, J. Legendziewicz, Indian J. Chem. A 43 (2004) 1403. [14] L.M.C. Beltran, J.R. Long, Acc. Chem. Res. 38 (2005) 325. [15] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319. [16] (a) Y.S. You, J.H. Yoon, J.H. Lim, H.C. Kim, C.S. Hong, Inorg. Chem. 44 (2005) 7063; (b) Y.S. You, D. Kim, Y. Do, S.J. Oh, C.S. Hong, Inorg. Chem. 43 (2004) 6899. [17] R.W. Hay, G.A. Lawrence, J. Chem. Soc., Dalton Trans. (1975) 1466. [18] S.-G. Kang, J.K. Kweon, S.-K. Jung, Bull. Korean Chem. Soc. 12 (1991) 483. [19] G.M. Sheldrick, SHELXTL, version 5, Bruker AXS, Madison, Wisconsin, 1995. [20] O. Kahn, Molecular Magnetism, VCH, Weinheim, 1993. [21] (a) R.L. Carlin, C.J. O’Connor, S.N. Bhatia, J. Am. Chem. Soc. 98 (1976) 3523; (b) P. King, R. Cle´rac, W. Wernsdorfer, C.E. Anson, A.K. Powell, Dalton Trans. (2004) 2670. [22] A. Meyer, A. Gleizes, J.J. Girerd, M. Verdaguer, O. Kahn, Inorg. Chem. 21 (1982) 1729. [23] M.E. Fisher, Am. J. Phys. 32 (1964) 343.
0.0 0
20000 40000 60000 80000 H (G)
0.25 0
50
100
150
200
250
300
T (K)
Fig. 8. Plot of vmT vs. T for 2. The solid line shows a best fit with a Cu(II) chain model. The inset provides the field dependence of the magnetization of 2 that is well reproduced by the Brillouin function for a noncoupled Cu(II) ion at 1.8 K.
4. Conclusion Two new coordination polymers assembled by [Fe(CN)5(NO)]2 and [M(macrocycle)]2+ (M = Ni, Cu) have been prepared and characterized in terms of structure and magnetism. Tuning molecular structures have been tested by a judicial choice of macrocyclic ligands that contain different steric motifs. The use of the planar macrocycle L1 allows for parallel chains (1) well stacked in a crystal packing diagram. However, the adoption of the flexible L2 ligand including bulky cyclohexyl and pendant methyl side groups leads to the formation of slanted chains of 2. From the structural analysis, it is elucidated that the close contacts between the bulky groups on L2 play a crucial role in rendering the chains tilted. This finding may benefit the development of new coordination compounds with the desired structures by adjusting bulkiness of side groups on macrocyclic coligands. The magnetic studies reveal that the long diamagnetic bridge, nitroprusside, between paramagnetic metal ions enables to transmit very weak antiferromagnetic couplings. 5. Supplementary material CCDC 620374 and 620375 contain the supplementary crystallographic data for 1 and 2. The data can be obtained free of charge via htpp://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc. cam.ac.uk. Acknowledgments This work was supported by Korea Research Foundation Grant funded by Korea Government (MOEHRD,
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531 [24] P.A. Berseth, J.J. Sokol, M.P. Shores, J.L. Heinrich, J.R. Long, J. Am. Chem. Soc. 122 (2000) 9655. [25] N. Fukita, M. Ohba, H. Okawa, K. Matsuda, H. Iwamura, Inorg. Chem. 37 (1998) 842. [26] (a) C.S. Hong, J.H. Yoon, J.H. Lim, H.H. Ko, Eur. J. Inorg. Chem. (2005) 4818;
2531
(b) C.S. Hong, Y.S. You, Polyhedron 23 (2004) 1379; (c) C.S. Hong, J.H. Yoon, Y.S. You, Inorg. Chim. Acta 358 (2005) 3341. [27] W.E. Estes, D.P. Gavel, W.E. Hatfield, D. Hodgson, Inorg. Chem. 17 (1978) 415.
Synthesis, structures, and magnetic properties of one-dimensional Fe–M (M = NiII, CuII) coordination polymers bridged by nitroprusside Young Sin You a, Jung Hee Yoon a, Jeong Hak Lim a, Hyoung Chan Kim b, Chang Seop Hong a,* a
Department of Chemistry and Center for Electro- and Photo-Responsive Molecules, Korea University, Seoul 136-701, Republic of Korea b Systems Research Team, Research and Development Division, Nuclear Fusion Research Center, Daejeon 305-333, Republic of Korea Received 21 September 2006; received in revised form 2 December 2006; accepted 8 December 2006 Available online 20 December 2006
Abstract Self-assembling [Fe(CN)5(NO)]2 and [M(L)]2+ (M = Ni, Cu; L = macrocycles) led to one-dimensional coordination polymers, [Ni(L1)][Fe(CN)5(NO)] Æ 2H2O (1) with parallel chains and [Cu(L2)][Fe(CN)5(NO)] Æ 3H2O (2) exhibiting a slanted chain structure. Compound 1 contains a planar macrocycle L1 coordinated to a slightly distorted octahedral Ni(II) ion in which the planarity of L1 gives rise to piling up chains in parallel. In contrast, a more flexible macrocyclic ligand L2 in 2 that surrounds a Cu center with a tetragonal elongation has bulky cyclohexyl groups together with pendant methyl side groups. The presence of the methyl groups on L2 in a chain makes the cyclohexyl groups in an adjacent chain tilted against the CuN4 basal plane with the methyl groups, eventually resulting in the slanted chain structure. Magnetic data demonstrate that antiferromagnetic interactions (J 0.13 cm1) are operating although the paramagnetic centers are linked by the long diamagnetic [Fe(CN)5(NO)]2 anion. 2006 Elsevier B.V. All rights reserved. Keywords: Nitroprusside; Coordination polymers; Crystal structures; Magnetic properties
1. Introduction Coordination polymers have been one of the active subjects because of emergent fascinating properties found in molecule-based magnetic materials with high TC [1], photo-induced magnetism [2], and magnetochiral effect [3], molecular nanomagnetism [4], and metal–organic frameworks [5] functioning for storage, exchange, and separation. To achieve such functional coordination materials cyanide-based complexes as bridges to link metal centers have been frequently used, in turn producing fruitful results exhibiting intriguing characters [6,7]. In the construction of magnetic bimetallic systems, the nitroprusside anion [Fe(CN)5(NO)]2 has not been explored extensively compared with other hexacyanometalates [M(CN)6]n (M = FeII/III, CrIII), because the precur*
Corresponding author. E-mail address: [email protected] (C.S. Hong).
0020-1693/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.12.023
sor is diamagnetic [8]. However, the use of the photochromic nitroprusside provided novel photomagnetic materials controlled by light irradiation as exemplified in Ni[Fe(CN)5(NO)] Æ 5.3H2O [9]. Moreover, the study on bimetallic coordination compounds bridged by nitroprusside is still an appealing theme because the nitroprusside bridge can serve as a good building block for multi-dimensional structures. Only a few examples were reported to date with diverse structures ranging from dinuclear molecules [10,11], one-dimensional chains [10,12], to twodimensional networks [10,13]. Since most of them have open polydentate coligands of diamines and triamines, chemical design of specific coordination environments for preprogrammed structures is promptly hampered by more than two binding sites for incoming donor atoms of bridging ligands, and therefore suitable systems aiming to tuning molecular structures merit to be sought. To fabricate tailor-made molecular architectures continual pursuits are to find a rational synthetic route that
2524
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
provides a clue to control overall structural patterns [14,15]. To this end, tetradentate macrocycles whose four nitrogens can coordinate the equatorial positions of an octahedral metal center are one of the proper coligands because the remaining two apical sites are solely available for coordination to bridging ligands and then contacts between molecules are readily influenced by the presence of side groups on the ligands [16]. Hence fine-tuning of molecular structures would result if one employs the macrocyclic ligands with various bulky side groups. Thus, the successful design of coordination compounds with desired structures would be one of the current issues to establish structure–property relationship on coordination materials.
N
HN
NH HN
N
NH HN
NH
L1
L2
Herein we report the syntheses, crystal structures, and magnetic properties of two one-dimensional coordination polymers, [Ni(L1)][Fe(CN)5(NO)] Æ 2H2O (1) and [Cu(L2)][Fe(CN)5(NO)] Æ 3H2O (2), chelated with tetradentate macrocyclic ligands. The molecular structure of compound 1 with a planar macrocyclic ligand L1 is extended by packing chains in parallel while, remarkably, chains in 2 are slanted to each other because of the steric effect of bulky cyclohexyl and methyl side groups on L2. Magnetic data show that the long diamagnetic nitroprusside spacer mediates weak antiferromagnetic interactions between paramagnetic metal centers.
in the dark gave pale yellow crystals in a yield of 55%. Anal. Calc. for C17H28FeN10NiO3: C, 38.2; H, 5.27; N, 26.2. Found: C, 38.0; H, 5.43; N, 26.5%. Selected IR data (KBr pellet): mCN = 2179, 2158, 2145, 2137 cm1, mNO = 1917 cm1. 2.1.3. Synthesis of [Cu(L2)][Fe(CN)5(NO)] Æ 3H2O (2) A DMF solution of [Cu(L2)](ClO4)2 (0.15 mmol) was added to Na2[Fe(CN)5(NO)] Æ 2H2O (0.15 mmol) dissolved in water. After stirring for a few minutes, the resulting solution was filtered. The filtrate was allowed to stand undisturbed in the dark, giving violet crystals in a yield of 68%. Anal. Calc. for C25H46CuFeN10O4: C, 44.8; H, 6.92; N, 20.9. Found: C, 44.7; H, 6.90; N, 20.6%. Selected IR data (KBr pellet): mCN = 2154, 2139 cm1, mNO = 1909 cm1. 2.2. Physical measurements Elemental analyses for C, H, and N were performed at the Elemental Analysis Service Center of Sogang University. Infrared spectra were obtained from KBr pellets with a Bomen MB-104 spectrometer. Magnetic susceptibilities for 1 and 2 were carried out using a Quantum Design MPMS-7 SQUID magnetometer. The susceptibility data were corrected for the sample holder and diamagnetic contributions from the samples using Pascal’s constants. 2.3. Crystallographic structure determination X-ray data for 1 and 2 were collected on a Bruker SMART APEXII diffractometer equipped with graphite ˚ ). The monochromated Mo Ka radiation (k = 0.71073 A reflection data were corrected for Lorentz and polarization factors. The structures were solved by direct methods and refined by full-matrix least-squares analysis using anisotropic thermal parameters for nonhydrogen atoms with
2. Experimental
Table 1 Crystal data and structure refinement for 1 and 2
2.1. Preparations
Compound
2.1.1. Materials [Ni(L1)](ClO4)2 [17] and [Cu(L2)](ClO4)2 [18] were prepared according to the literature methods. All of the other chemicals and solvents are commercially available and used as received. All manipulations were performed under aerobic conditions. Caution: Perchlorate salts of metal compounds with organic ligands are potentially explosive. Only small amounts of material should be cautiously handled. 2.1.2. Synthesis of [Ni(L1)][Fe(CN)5(NO)] Æ 2H2O (1) A DMF solution of [Ni(L1)](ClO4)2 (0.2 mmol) was treated with Na2[Fe(CN)5(NO)] Æ 2H2O (0.20 mmol) dissolved in water. The resultant mixture was stirred for 10 min and filtered. The slow evaporation of the solution
1
Empirical formula C17H28FeN10NiO3 Formula weight 535.05 Crystal system monoclinic Space group P21/n ˚) a (A 11.4040(2) ˚) b (A 14.3070(3) ˚) c (A 14.9021(3) b () 100.3570(10) ˚ 3) V (A 2391.77(8) Z 4 l (mm1) 1.433 1.486 q (g cm3) F(0 0 0) 1112 Goodness-of-fit 1.059 R1a [I > 2r(I)] 0.0570 wR2b [I > 2r(I)] 0.1353 P P a R1 = iFoj jFci/ jFcj. P P b wR2 ¼ ½ wðF 2o F 2c Þ2 = wðF 2o Þ2 1=2 .
2 C25H46CuFeN10O4 670.11 monoclinic Cc 19.0742(5) 8.5204(3) 18.8634(6) 101.3840(10) 3005.36(16) 4 1.239 1.481 1412 1.079 0.0233 0.0642
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
the SHELXTL program [19]. All hydrogen atoms except for hydrogens bound to water molecules were calculated at idealized positions and refined with the riding models. Crystallographic data and the details of data collection are listed in Table 1. 3. Results and discussion 3.1. Synthesis and characterization The title compounds were prepared by a reaction mixture of the [Fe(CN)5(NO)]2 dianion and [M(L)](ClO4)2 (M = Ni, Cu; L = L1, L2) where the reaction progress was readily checked by the absence of the IR peaks characteristic of ClO4 anion of the M precursor. The distinct IR absorption bands in the range 2200–1900 cm1 concern CN and linear NO+ stretchings. The CN vibrations are observed at 2179, 2158, 2145, 2137 cm1 for 1 and 2154, 2139 cm1 for 2, respectively, which are in good agreement with other compounds containing nitroprusside [10–13]. Single strong bands centered at 1917 cm1 for 1 and 1909 cm1 for 2 can be attributed to the NO stretching frequency. The vibrations are situated lower than that observed for the nitroprusside anion (1939 cm1), which also coincides with nitroprusside-linked systems [10–13]. 3.2. Description of the structures 3.2.1. Complex 1 An ORTEP diagram of 1 is depicted in Fig. 1. Selected bond distances and angles are summarized in Table 2. The crystal structure of 1 is formed by nitroprusside anion and [Ni(L1)]2+ cation. The structural aspect around the Fe ion of nitroprusside can be described as a regular octahedron consisting of five CN groups with Fe–C distances spanning ˚ and one NO group with a Fe–N from 1.936 to 1.953 A ˚ , shorter than the Fe–C bond lengths. length of 1.662(4) A The Fe–CN and Fe–NO angles are almost linear, ranging from 172.8 to 179.4. These structural parameters are con-
Fig. 1. ORTEP diagram of 1 with the atom-labeling scheme. Symmetry code: (i) x + 1/2, y + 1/2, z 1/2.
2525
Table 2 ˚ ) and angles () for 1a Selected bond lengths (A Fe(1)–N(6) Fe(1)–C(1) Fe(1)–C(5) N(1)–Ni(1) Ni(1)–N(10) Ni(1)–N(9) N(6)–Fe(1)–C(2) C(2)–Fe(1)–C(1) C(2)–Fe(1)–C(4) N(6)–Fe(1)–C(5) C(1)–Fe(1)–C(5) N(6)–Fe(1)–C(3) C(1)–Fe(1)–C(3) C(5)–Fe(1)–C(3) C(1)–N(1)–Ni(1) N(3)–C(3)–Fe(1) C(4)i–N(4)–Ni(1) O(1)–N(6)–Fe(1) N(10)–Ni(1)–N(9) N(10)–Ni(1)–N(7) N(9)–Ni(1)–N(7) N(8)–Ni(1)–N(1) N(7)–Ni(1)–N(1) N(8)–Ni(1)–N(4) N(7)–Ni(1)–N(4) C(6)–N(7)–Ni(1) C(9)–N(8)–Ni(1) C(12)–N(9)–Ni(1) C(15)–N(10)–Ni(1)
1.662(4) 1.937(4) 1.946(5) 2.090(3) 1.998(5) 2.022(4) 94.92(18) 89.51(16) 88.05(16) 95.44(17) 89.24(16) 178.83(16) 85.41(16) 85.38(17) 161.2(3) 179.4(4) 161.4(3) 177.3(3) 85.9(2) 93.4(2) 176.75(15) 88.17(15) 88.53(14) 90.37(15) 91.13(14) 107.0(3) 145.6(7) 108.0(3) 147.0(7)
Fe(1)–C(2) Fe(1)–C(4) Fe(1)–C(3) N(4)i–Ni(1) Ni(1)–N(8) Ni(1)–N(7) N(6)–Fe(1)–C(1) N(6)–Fe(1)–C(4) C(1)–Fe(1)–C(4) C(2)–Fe(1)–C(5) C(4)–Fe(1)–C(5) C(2)–Fe(1)–C(3) C(4)–Fe(1)–C(3) N(1)–C(1)–Fe(1) N(2)–C(2)–Fe(1) N(4)ii–C(4)–Fe(1) N(5)–C(5)–Fe(1) N(10)–Ni(1)–N(8) N(8)–Ni(1)–N(9) N(8)–Ni(1)–N(7) N(10)–Ni(1)–N(1) N(9)–Ni(1)–N(1) N(10)–Ni(1)–N(4) N(9)–Ni(1)–N(4) N(1)–Ni(1)–N(4) C(17)–N(7)–Ni(1) C(7)–N(8)–Ni(1) C(11)–N(9)–Ni(1) C(13)–N(10)–Ni(1)
1.936(4) 1.942(4) 1.953(4) 2.130(3) 2.003(5) 2.033(4) 95.42(16) 92.69(16) 171.71(17) 169.64(17) 91.73(16) 84.27(18) 86.46(16) 179.2(4) 179.5(4) 172.8(4) 178.7(4) 178.47(18) 94.5(2) 86.3(2) 93.33(15) 88.36(14) 88.14(15) 92.01(14) 178.51(13) 108.7(3) 108.3(4) 109.9(3) 109.1(4)
a Symmetry transformations used to generate equivalent atoms: (i) x + 1/2, y + 1/2, z 1/2; (ii) x 1/2, y + 1/2, z + 1/2.
sistent with those reported for bimetallic compounds with [Fe(CN)5(NO)]2 anion [10–13]. The Ni atom adopts a distorted octahedral geometry composed of four equatorial ˚ ) and two axial N N atoms from L1 (av Ni–N = 2.01(2) A atoms from bridging CN ligands (Ni1–N1 = 2.090(3), ˚ ; i = 0.5 + x, 0.5 y, 0.5 + z). Ni1–N4i = 2.123(3) A The equatorial NiN4 plane is virtually planar with the larg˚ at est deviation from the least-squares plane of 0.0412 A N10. The presence of sp2 carbons (C9 and C15) and nitrogens (N8 and N10) on L1 establishes planarity with linked neighboring atoms, while the other carbon atoms (C6, C11, ˚ C12, C17) on L1 lie with a mean deviation of 0.57(3) A from the basal plane toward N4i. The bridging cyanides axially coordinate to the Ni center, forming a small bent angle of Ni–NC = 161.3(1). The nearly planar structure of L1 is not prone to cause a steric effect toward [Fe(CN)5(NO)]2 unit, which is responsible for such a bending of the Ni–NC angle. The coordination chains of 1, constructed by self-assembling the nitroprusside and Ni precursor, are well packed in a three-dimensional pattern as seen in Fig. 2. The position of the NO groups on nitroprussides is varied alternately along the chain. The shortest intrachain distance is ˚ for Fe–Ni and 10.165 A ˚ for Ni–Ni. In Fig. 2a, 5.099 A the shortest contact between chains is found to be ˚ between N9 on L1 and N5 on CN group, which 3.086 A is smaller than the sum of the van der Waals radii
2526
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
Fig. 2. Extended molecular view of 1 displaying packing feature of chains in the bc-plane (a) and ac-plane (b). The representative shortest contacts between chains are indicated as dotted lines. Colors denote Fe in pink, Ni in green, N in blue, O in red, and C in grey. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
˚ ). The shortest interchain M–M distances are (3.10 A ˚ for Ni–Ni, 8.013 A ˚ for Fe–Ni, and 9.059 A ˚ for 8.270 A Fe–Fe. In comparison, Fig. 2b reveals that the closest sep˚ between C8 aration between chains corresponds to 3.365 A on L1 and O1 on NO group, which is a little longer than ˚ ). The shortest the sum of the van der Waals radii (3.22 A ˚ for Ni–Ni, 8.665 A ˚ interchain M–M distances are 8.531 A ˚ for Fe–Fe. The observation of for Fe–Ni, and 8.574 A the shorter distance for Fe–Ni in Fig. 2a compared with that in Fig. 2b could be pertinent to some kind of interchain interactions occurring between N9 and N5. A number of hydrogen bonds are formed among lattice water molecules, CN, and NO groups. Thus, the inclusion of the planar macrocycle L1 into coordination polymers helps to construct parallel chains by stacking them regularly in this system. 3.2.2. Complex 2 An ORTEP diagram of 2 is displayed in Fig. 3. Selected bond distances and angles are tabulated in Table 3. The structural parameters in an octahedral Fe center ˚ and exhibit an average Fe–C bond length of 1.940(6) A
Fig. 3. Molecular views of (a) the asymmetric unit with the atom-labeling scheme and (b) showing a one-dimensional chain structure of 2. Symmetry code: (i) x + 1/2, y 1/2, z. Colors represent Fe in pink, Cu in brown, N in blue, O in red, and C in grey. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
˚ , which are quite similar to those Fe–N of 1.6585(16) A of 1. The Fe–C(N)–N(O) angles in the range 174.48– 179.35 are close to linearity. The Cu ion resides in a distorted octahedral arrangement, occupied by four equato˚ ) and two rial N atoms from L2 (av Cu–N = 2.04(2) A apical N atoms from bridging CN groups (Cu1– ˚ , Cu1–N2i = 2.5638(17) A ˚ ; i = 0.5 x, N1 = 2.4458(16) A 0.5 + y, z). The tetragonally elongated environment around the Cu center is definitely associated with the Jahn–Teller effect of an octahedral Cu(II) ion. A noticeable structural feature is that the methyl side groups of the macrocycle L2 stand virtually upright with respect to the CuN4 basal plane (Fig. 3b), functioning as a steric object. In fact, the bond angle of Cu–NC (cyanide) remains substantially bent, being 139.96(14) for Cu1– N1–C1, which is quite smaller than the corresponding Ni–NC angle of 161.3(1) for 1. It is also worthy of noting that unlike L1, L2 includes two bulky cyclohexyl groups, which would critically affect the overall structural patterns. The NO groups are on the same side in a chain ˚ for Fe– and the shortest intrachain distances are 5.176 A ˚ Cu and 10.445 A for Cu–Cu. Fig. 4 shows a three-dimensional packing diagram in which two kinds of chains, indicated by blue and orange
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531 Table 3 ˚ ) and angles () for 2a Selected bond lengths (A Fe(1)–N(6) Fe(1)–C(2) Fe(1)–C(3) N(1)–Cu(1) Cu(1)–N(8) Cu(1)–N(9) N(6)–Fe(1)–C(1) C(1)–Fe(1)–C(2) C(1)–Fe(1)–C(5) N(6)–Fe(1)–C(3) C(2)–Fe(1)–C(3) N(6)–Fe(1)–C(4) C(2)–Fe(1)–C(4) C(3)–Fe(1)–C(4) C(1)–N(1)–Cu(1) N(3)–C(3)–Fe(1) N(5)–C(5)–Fe(1) N(8)–Cu(1)–N(10) N(10)–Cu(1)–N(9) N(10)–Cu(1)–N(7) N(8)–Cu(1)–N(1) N(9)–Cu(1)–N(1) C(6)–N(7)–Cu(1) C(12)–N(8)–Cu(1) C(16)–N(9)–Cu(1) C(22)–N(10)–Cu(1)
1.6585(16) 1.9382(18) 1.944(2) 2.4458(16) 2.0213(15) 2.0591(14) 94.98(8) 170.34(8) 90.70(7) 96.32(8) 90.34(7) 178.69(9) 85.24(8) 84.99(8) 139.96(14) 179.21(17) 178.00(17) 179.25(8) 85.01(6) 94.75(6) 89.53(6) 85.19(6) 107.75(11) 114.77(11) 107.93(11) 114.24(11)
Fe(1)–C(1) Fe(1)–C(5) Fe(1)–C(4) Cu(1)–N2i Cu(1)–N(10) Cu(1)–N(7) N(6)–Fe(1)–C(2) N(6)–Fe(1)–C(5) C(2)–Fe(1)–C(5) C(1)–Fe(1)–C(3) C(5)–Fe(1)–C(3) C(1)–Fe(1)–C(4) C(5)–Fe(1)–C(4) N(1)–C(1)–Fe(1) N(2)–C(2)–Fe(1) N(4)–C(4)–Fe(1) O(1)–N(6)–Fe(1) N(8)–Cu(1)–N(9) N(8)–Cu(1)–N(7) N(9)–Cu(1)–N(7) N(10)–Cu(1)–N(1) N(7)–Cu(1)–N(1) C(24)–N(7)–Cu(1) C(11)–N(8)–Cu(1) C(14)–N(9)–Cu(1) C(21)–N(10)–Cu(1)
1.9305(18) 1.9400(19) 1.9457(19) 2.5638(17) 2.0272(15) 2.0627(15) 94.62(8) 93.47(8) 87.63(8) 89.69(7) 170.13(8) 85.15(8) 85.22(8) 177.55(16) 174.48(16) 179.35(18) 177.50(16) 95.20(6) 85.03(6) 178.71(7) 91.20(6) 96.08(6) 121.73(11) 108.39(11) 121.55(11) 107.58(11)
a Symmetry transformations used to generate equivalent atoms: (i) x + 1/2, y 1/2, z.
2527
˚ , N5– propyl backbones on L2 (N3–C23 = 3.395 A ˚ C13 = 3.372 A). The shortest interchain M–M separations ˚ for Fe–Fe and Cu–Cu, 7.826 A ˚ for Fe–Cu. On are 8.520 A the other hand, the respective cyclohexyl groups from orange and blue chains become close as given in Fig. 5b, strikingly leading to the formation of such slanted chains. At contact points of the two chains the shortest distances among cyanides, cyclohexyl, and methyl groups are ˚ for C15–C10, 3.463 A ˚ for N3–C8, 3.569 A ˚ for 4.098 A ˚ N5–C18, and 4.034 A for C25–C20, respectively. The most important factor to govern the observed tilted structure is likely the interchain interactions between the methyl and cyclohexyl groups where a methyl moiety on one orange chain can push away a cyclohexyl unit on the other blue chain and render the ring of the corresponding group slanted with respect to the CuN4 basal plane on the orange chain. The shortest interchain separations between metal ions on the blue and orange chains, respectively, are rather ˚ for Fe–Fe, 9.801 A ˚ for Fe–Cu, longer, being 9.435 A 10.316 for Cu–Cu, which result from the orientation of the bulky cyclohexyl groups between the chains. Consequently, it is manifest that the protruded side groups of the macrocyclic ligand L2 play a pivotal role in attaining the atypical structural type in this system. Many hydrogen bonds among lattice water molecules, CN, and NO groups are present in 2. 3.3. Magnetic properties
colors, are running in a tilted fashion. This structural peculiarity in 2 is wholly intriguing and obviously different from that of 1. As shown in Fig. 5a, the bulky cyclohexyl groups are positioned away from each other and do not participate in stacking the blue chains in a parallel manner. Thus, the close contacts are mainly achieved between cyanide and
For 1, the vmT value of 1.23 cm3 K mol1 at 300 K is close to the spin-only one (1.00 cm3 K mol1) expected for a noninteracting Ni(II) (S = 1) ion (Fig. 6). The [Fe(CN)5(NO)]2 anion is known to be diamagnetic because of the formation of an electron pair between
Fig. 4. Three-dimensional structure in the ab-plane of 2. The blue and orange chains are located tilted to each other. The lattice water molecules are indicated in red. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
2528
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
Fig. 5. Extended molecular structure of 2 illustrating (a) parallel stacked chains (blue) and (b) slanted chains (blue and orange) in the different layers. The closest contacts between adjacent chains are indicated as dotted lines. (For interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)
unpaired electrons of the low-spin Fe(III) and nitrosyl free radical [9–13]. As the temperature is lowered, vmT decreases slowly and below 40 K drops down to 0.477 cm3 K mol1 at 1.8 K.
Since the Ni(II) ion in 1 is in the axially distorted octahedral surrounding, the magnetic data can be fitted using the equation including zero-field splitting and ignoring intrachain interactions, defined as
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
vz ¼ ð2Ng2 b2 =kT Þ½expðD=kT Þ=ð1 þ 2 expðD=kT ÞÞ 2 2
vx ¼ ð2Ng b =DÞf½1 expðD=kT Þ=½1 þ 2 expðD=kT Þg vm ¼ ðvz þ 2vx Þ=3 ð1Þ where vz is the parallel magnetic susceptibility, vx the perpendicular magnetic susceptibility, and D the axial zero-field splitting parameter [20]. The best result gives g = 2.211 and D = 6.54 cm1, in accordance with the reported values [21]. But the high-temperature magnetic data were not well reproduced with this model. When temperature-independent paramagnetism (TIP) was included, the parameters are g = 2.21, D = 6.50 cm1, and TIP = 3.0 · 105 cm3 mol1, still giving a poor fit in the high-temperature region. This implies that intrachain magnetic contribution through the diamagnetic nitroprusside spacer could be taken into account. To quantify magnetic interactions along the chain, an analytical expression for S = 1 on the basis of the spin Hamiltonian H = JRiSAi Æ SAi+1 was employed in the temperature range of 20–300 K where the local anisotropy is neglected [22] vm ¼ ðNg2 b2 =kT Þ½ð1:0 þ 0:0194x þ 0:777x2 Þ =ð3:0 þ 4:346x þ 3:232x2 þ 5:834x3 Þ
ð2Þ
with x = jJj/kT. The fitting of the experimental data with Eq. (2) produces g = 2.21, J = 0.13 cm1, and TIP = 0. These magnetic data can also be treated by taking an infinite chain model of classical spins derived by Fisher [23] vm ¼ ½Ng2 b2 SðS þ 1Þ=kT ½ð1 þ uÞ=ð1 uÞ
ð3Þ
with u = coth[JS(S + 1)/kT] kT/[JS(S + 1)]. The fitting result corresponds to g = 2.21, J = 0.14 cm1, and TIP = 0. As shown in the inset of Fig. 6, the theoretical curves of the two magnetic chain models are actually superimposed and well reproduce the vmT product in the high temperature regime. Therefore, despite the long separa˚ ) via [Fe(CN)5(NO)]2 the very weak intrachain tion (>10 A
2529
antiferromagnetic interaction is operative, which is consistent with a one-dimensional Cu–Fe bimetallic system in which the paramagnetic Cu centers are bridged by the nitroprusside [12b]. This has been demonstrated on numerous occasions, for instance, in the case of antiferromagnetic or ferromagnetic interactions mediated by the diamagnetic NiðCNÞ4 2 or ferrocyanide bridges [24,25]. The obtained J value falls into the normal range of magnetic strength for nitroprusside or terephthalate-bridged complexes where ˚ the bridging ligands link two metal centers within 10–11 A [12b,26]. The field dependence of the magnetization for 1 was collected at 1.8 K in the field range 0–7 T (Fig. 7). The magnetization data are lower than the Brillouin curve deduced for an isolated Ni(II) spin with g = 2.21, demonstrating that at 1.8 K the weak antiferromagnetic couplings and zero-field splitting exist. The weak contributions are overcome by raising a magnetic field up to 7 T, eventually reaching a saturation value. For 2, the vmT value is equal to 0.42 cm3 K mol1 at 300 K, consistent with the spin-only one (0.375 cm3 K mol1) expected for an uncoupled Cu(II) ion (Fig. 8). The vmT on coupling goes on a slow decrease and then drops abruptly, arriving at 0.39 cm3 K mol1 at 1.8 K. The magnetic data can be interpreted with a numerical expression based on the spin Hamiltonian H = JRiSAi Æ SAi+1 [27] vm ¼ ðNg2 b2 =kT Þ½ð0:25 þ 0:074975x þ 0:075235x2 Þ =ð1:0 þ 0:9931x þ 0:172135x2 þ 0:757825x3 Þ
ð4Þ
with x = jJj/kT. The best fit yields g = 2.12(1) and J = 0.12(1) cm1, indicating the presence of weak antiferromagnetic interactions mediated by nitroprusside. The magnitude of magnetic exchange coupling in 2 is analogous to 1 and metal compounds bridged by nitroprusside or terephthalate [12b,26]. Such weak couplings are also confirmed by the M(H) data where the magnetization data in the low field regime are slightly lower than the Brillouin curve calculated from g = 2.12 and S = 1/2 (inset of Fig. 8).
1.2 2.0 -1
T (cm K mol )
1.0
1.22
1.5
m
M (N )
3
0.8
m
3
-1
T (cm K mol )
1.23
0.6
1.21 0
100
200
1.0
300
T (K)
0.5
0.4 0
50
100
150
200
250
300
T (K)
0.0 0
Fig. 6. Plot of vmT vs. T for 1. The inset is the blow-up of the vmT product. The theoretical fits are derived from an isolated Ni(II) model containing zero-field splitting with (dashed line) and without TIP (dotted line) and 1D Ni(II) chain models (solid line), respectively.
20000
40000
60000
80000
H (G)
Fig. 7. Field dependence of the magnetization for 1. The Brillouin curve for a noninteracting Ni(II) (S = 1) is drawn at 1.8 K.
2530
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531
Basic Research Promotion Fund) (KRF-2005-070C00068) and CRM-KOSEF. We also thank an Operation Program on Shared Research Equipment of KBSI and MOST.
0.45
1.2
M (N )
-1
T (cm K mol )
0.40
m
3
0.35
0.30
0.8
References
0.4
[1] S.M. Holmes, G.S. Girolami, J. Am. Chem. Soc. 121 (1999) 5593. [2] A. Dei, Angew. Chem., Int. Ed. 44 (2005) 1160. [3] E.-Q. Gao, Y.-F. Yue, S.-Q. Bai, Z. He, C.-H. Yan, J. Am. Chem. Soc. 126 (2004) 1419. [4] D. Gatteschi, R. Sessoli, Angew. Chem., Int. Ed. 42 (2003) 268. [5] S.L. James, Chem. Soc. Rev. 32 (2003) 276. [6] (a) S.-i. Ohkoshi, H. Tokoro, T. Hozumi, Y. Zhang, K. Hashimoto, C. Mathonie´re, I. Bord, G. Rombaut, M. Verelst, C. Cartier dit Moulin, F. Villain, J. Am. Chem. Soc. 128 (2006) 270; (b) H. Imai, K. Inoue, K. Kikuchi, Y. Yoshida, M. Ito, T. Sunahara, S. Onaka, Angew. Chem., Int. Ed. 43 (2004) 5618. [7] S. Kitagawa, R. Kitaura, S.-i. Noro, Angew. Chem., Int. Ed. 43 (2004) 2334. [8] (a) M. Ohba, H. Okawa, N. Fukita, Y. Hashimoto, J. Am. Chem. Soc. 119 (1997) 1011; (b) H.-Z. Kou, S. Gao, O. Bai, Z.-M. Wang, Inorg. Chem. 40 (2001) 6287; (c) E. Colacio, M. Ghazi, H. Stoeckli-Evans, F. Lloret, J.M. Moreno, C. Pe´rez, Inorg. Chem. 40 (2001) 4876. [9] Z.-Z. Gu, O. Sato, T. Iyoda, K. Hashimoto, A. Fujishima, Chem. Mater. 9 (1997) 1092. [10] (a) M. Clemente-Leo´n, E. Coronado, J.R. Gala´n-Mascaro´s, C.J. Go´mez-Garcı´a, Th. Woike, J.M. Clemente-Juan, Inorg. Chem. 40 (2001) 87; (b) B. Bellouard, M. Clemente-Leo´n, E. Coronado, J.R. Gla´nMascaro´s, C. Gime´nez-Saiz, C.J. Go´mez-Garcı´a, Th. Woike, Polyhedron 20 (2001) 1615. [11] (a) H.L. Shyu, H.-H. Wei, J. Coord. Chem. 47 (1999) 319; (b) K.L. Zhang, Y. Xu, Z. Wang, C.M. Jin, X.Z. You, Trans. Met. Chem. 27 (2002) 95; (c) Z. Smekal, Z. Travnicek, J. Marek, M. Nadvornik, Aust. J. Chem. 53 (2000) 225. [12] (a) H.L. Shyu, H.H. Wei, Y. Wang, Inorg. Chim. Acta 258 (1997) 81; (b) H.Z. Kou, H.M. Wang, D.Z. Liao, P. Cheng, Z.H. Jiang, S.P. Yan, X.Y. Huang, G.L. Wang, Aust. J. Chem. 51 (1998) 661. [13] N. Shaikh, A. Panja, S. Goswami, P. Banerjee, M. Kubiak, Z. Ciunik, M. Puchalska, J. Legendziewicz, Indian J. Chem. A 43 (2004) 1403. [14] L.M.C. Beltran, J.R. Long, Acc. Chem. Res. 38 (2005) 325. [15] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319. [16] (a) Y.S. You, J.H. Yoon, J.H. Lim, H.C. Kim, C.S. Hong, Inorg. Chem. 44 (2005) 7063; (b) Y.S. You, D. Kim, Y. Do, S.J. Oh, C.S. Hong, Inorg. Chem. 43 (2004) 6899. [17] R.W. Hay, G.A. Lawrence, J. Chem. Soc., Dalton Trans. (1975) 1466. [18] S.-G. Kang, J.K. Kweon, S.-K. Jung, Bull. Korean Chem. Soc. 12 (1991) 483. [19] G.M. Sheldrick, SHELXTL, version 5, Bruker AXS, Madison, Wisconsin, 1995. [20] O. Kahn, Molecular Magnetism, VCH, Weinheim, 1993. [21] (a) R.L. Carlin, C.J. O’Connor, S.N. Bhatia, J. Am. Chem. Soc. 98 (1976) 3523; (b) P. King, R. Cle´rac, W. Wernsdorfer, C.E. Anson, A.K. Powell, Dalton Trans. (2004) 2670. [22] A. Meyer, A. Gleizes, J.J. Girerd, M. Verdaguer, O. Kahn, Inorg. Chem. 21 (1982) 1729. [23] M.E. Fisher, Am. J. Phys. 32 (1964) 343.
0.0 0
20000 40000 60000 80000 H (G)
0.25 0
50
100
150
200
250
300
T (K)
Fig. 8. Plot of vmT vs. T for 2. The solid line shows a best fit with a Cu(II) chain model. The inset provides the field dependence of the magnetization of 2 that is well reproduced by the Brillouin function for a noncoupled Cu(II) ion at 1.8 K.
4. Conclusion Two new coordination polymers assembled by [Fe(CN)5(NO)]2 and [M(macrocycle)]2+ (M = Ni, Cu) have been prepared and characterized in terms of structure and magnetism. Tuning molecular structures have been tested by a judicial choice of macrocyclic ligands that contain different steric motifs. The use of the planar macrocycle L1 allows for parallel chains (1) well stacked in a crystal packing diagram. However, the adoption of the flexible L2 ligand including bulky cyclohexyl and pendant methyl side groups leads to the formation of slanted chains of 2. From the structural analysis, it is elucidated that the close contacts between the bulky groups on L2 play a crucial role in rendering the chains tilted. This finding may benefit the development of new coordination compounds with the desired structures by adjusting bulkiness of side groups on macrocyclic coligands. The magnetic studies reveal that the long diamagnetic bridge, nitroprusside, between paramagnetic metal ions enables to transmit very weak antiferromagnetic couplings. 5. Supplementary material CCDC 620374 and 620375 contain the supplementary crystallographic data for 1 and 2. The data can be obtained free of charge via htpp://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc. cam.ac.uk. Acknowledgments This work was supported by Korea Research Foundation Grant funded by Korea Government (MOEHRD,
Y.S. You et al. / Inorganica Chimica Acta 360 (2007) 2523–2531 [24] P.A. Berseth, J.J. Sokol, M.P. Shores, J.L. Heinrich, J.R. Long, J. Am. Chem. Soc. 122 (2000) 9655. [25] N. Fukita, M. Ohba, H. Okawa, K. Matsuda, H. Iwamura, Inorg. Chem. 37 (1998) 842. [26] (a) C.S. Hong, J.H. Yoon, J.H. Lim, H.H. Ko, Eur. J. Inorg. Chem. (2005) 4818;
2531
(b) C.S. Hong, Y.S. You, Polyhedron 23 (2004) 1379; (c) C.S. Hong, J.H. Yoon, Y.S. You, Inorg. Chim. Acta 358 (2005) 3341. [27] W.E. Estes, D.P. Gavel, W.E. Hatfield, D. Hodgson, Inorg. Chem. 17 (1978) 415.