Tetra-μ-benzoato-bis­[(quinoxaline)copper(II)]

Lee, E.Y.; Park, B.K.; Kim, C.; Kim, S.-J.; Kim, Y.

doi:10.1107/S1600536807067876

metal-organic compounds

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ISSN: 2056-9890

Volume 64| Part 2| February 2008| Page m286

doi:10.1107/S1600536807067876

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Tetra-μ-benzoato-bis[(quinoxaline)copper(II)]

Eun Yong Lee,^a Byeong Kwon Park,^a Cheal Kim,^a ^* Sung-Jin Kim ^b and Youngmee Kim ^b ^*

^aDepartment of Fine Chemistry, Eco-Product and Materials Education Center, Seoul National University of Technology, Seoul 139-743, Republic of Korea, and ^bDivision of Nano Sciences, Ewha Womans University, Seoul 120-750, Republic of Korea
^*Correspondence e-mail: chealkim@sunt.ac.kr, ymeekim@ewha.ac.kr

(Received 6 December 2007; accepted 20 December 2007; online 4 January 2008)

The paddlewheel-type centrosymmetric dinuclear title complex, [Cu₂(C₇H₅O₂)₄(C₈H₆N₂)₂], contains four bridging benzoate groups and two terminal quinoxaline ligands. The octahedral coordination around each Cu atom, with four O atoms in the equatorial plane, is completed by an N atom of a quinoxaline molecule [Cu—N = 2.2465 (18) Å] and by the second Cu atom [Cu⋯Cu = 2.668 (5) Å]. The Cu atom is 0.216 Å out of the plane of the four O atoms.

Related literature

For the related structure, Cu₂(O₂CPh)₄(py)₂ (py = pyridine), see: Speier & Fülöp (1989 ). For background information, see: Cotton & Walton (1993 ); Pichon et al. (2007 ); Goto et al. (2007 ); Takamizawa et al. (2004 ); Casarin et al. (2005 ); Deka et al. (2006 ).

Experimental

Crystal data

[Cu₂(C₇H₅O₂)₄(C₈H₆N₂)₂]
M_r = 871.82
Triclinic, $[P \overline 1]$
a = 10.1423 (16) Å
b = 10.3400 (17) Å
c = 10.5148 (17) Å
α = 65.459 (2)°
β = 73.063 (3)°
γ = 82.142 (3)°
V = 959.4 (3) Å³
Z = 1
Mo Kα radiation
μ = 1.17 mm⁻¹
T = 293 (2) K
0.15 × 0.10 × 0.08 mm

Data collection

Bruker SMART CCD area-detector diffractometer
Absorption correction: none
5377 measured reflections
3668 independent reflections
2983 reflections with I > 2σ(I)
R_int = 0.031

Refinement

R[F² > 2σ(F²)] = 0.033
wR(F²) = 0.080
S = 0.96
3668 reflections
262 parameters
H-atom parameters constrained
Δρ_max = 0.28 e Å⁻³
Δρ_min = −0.41 e Å⁻³

Data collection: SMART (Bruker, 1997 ); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998 ); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536807067876/dn2301sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536807067876/dn2301Isup2.hkl

checkCIF report

Comment top

The dinuclear metal carboxylates, M₂(O₂CR)₄, are important for the study of structures and metal-metal interaction (Cotton & Walton, 1993). Among them copper(II) carboxylates are used as building blocks to form a pillard-grid MOF with large pores (Pichon et al., 2007), and copper(II) benzoate pyrazine is used as the organic-inorganic hybrid complex that adsorbs gas molecules through clathrate formation (Goto et al., 2007, Takamizawa et al., 2004). Due to different coordination modes of carboxylates (Casarin et al., 2005), it is essential to have control on the binding of carboxylate to a metal ion in specific manner in the presence of other ligands (Deka et al., 2006). Controlling the binding of carboxylate will make it possible to synthesize complexes having new structures. We report here on the structure of new copper(II) benzoate with quinoxaline.

Asymmetric unit contains half of whole molecule, and there is an inversion center in the middle of Cu—Cu bond. Symmetric operation (-x + 2, -y + 1, -z + 1) produces a paddle-wheel type dinuclear copper-benzoate complex (Fig. 1). The paddle-wheel type dinuclear complex is constructed by four bridging benzoate groups and two terminal quinoxaline ligands. The octahedral coordination around the copper atom is completed by nitrogen atom of quinoxaline molecule (Cu—N 2.2465 (18) Å) and by the second copper atom (Cu···Cu 2.668 (5) Å). The copper atom is 0.216 Å out of the plane of the four oxygen atoms.

Related literature top

For the related structure, Cu₂(O₂CPh)₄(py)₂, see: Speier & Fülöp (1989) [please define Ph and py]. For background information, see: Cotton & Walton (1993); Pichon et al. (2007); Goto et al. (2007); Takamizawa et al. (2004); Casarin et al. (2005); Deka et al. (2006).

Experimental top

19.0 mg (0.1 mmol) of Cu(NO₃)₂.2.5H₂O and 28.0 mg (0.2 mmol) of C₆H₅COONH₄ were dissolved in 4 ml me thanol and carefully layered by 4 ml acetone solution of quinoxaline ligand (26.0 mg, 0.2 mmol). Suitable crystals of the title compound for X-ray analysis were obtained in a few weeks.

Computing details top

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: SHELXTL (Bruker, 1998).

Figures top

Fig. 1. The structure of the title compound showing the atom-labeling scheme. Displacement ellipsoids are shown at the 30% probability level.

Tetra-µ-benzoato-bis[(quinoxaline)copper(II)] top

Crystal data top

[Cu₂(C₇H₅O₂)₄(C₈H₆N₂)₂]	Z = 1
M_r = 871.82	F(000) = 446
Triclinic, P1	D_x = 1.509 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 10.1423 (16) Å	Cell parameters from 2414 reflections
b = 10.3400 (17) Å	θ = 2.4–27.2°
c = 10.5148 (17) Å	µ = 1.17 mm⁻¹
α = 65.459 (2)°	T = 293 K
β = 73.063 (3)°	Block, blue
γ = 82.142 (3)°	0.15 × 0.10 × 0.08 mm
V = 959.4 (3) Å³

Data collection top

Bruker SMART CCD area-detector diffractometer	2983 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.031
Graphite monochromator	θ_max = 26.0°, θ_min = 2.1°
ϕ and ω scans	h = −6→12
5377 measured reflections	k = −12→12
3668 independent reflections	l = −11→12

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.080	H-atom parameters constrained
S = 0.96	w = 1/[σ²(F_o²) + (0.0403P)²] where P = (F_o² + 2F_c²)/3
3668 reflections	(Δ/σ)_max = 0.002
262 parameters	Δρ_max = 0.28 e Å⁻³
0 restraints	Δρ_min = −0.41 e Å⁻³

Crystal data top

[Cu₂(C₇H₅O₂)₄(C₈H₆N₂)₂]	γ = 82.142 (3)°
M_r = 871.82	V = 959.4 (3) Å³
Triclinic, P1	Z = 1
a = 10.1423 (16) Å	Mo Kα radiation
b = 10.3400 (17) Å	µ = 1.17 mm⁻¹
c = 10.5148 (17) Å	T = 293 K
α = 65.459 (2)°	0.15 × 0.10 × 0.08 mm
β = 73.063 (3)°

Data collection top

Bruker SMART CCD area-detector diffractometer	2983 reflections with I > 2σ(I)
5377 measured reflections	R_int = 0.031
3668 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.033	0 restraints
wR(F²) = 0.080	H-atom parameters constrained
S = 0.96	Δρ_max = 0.28 e Å⁻³
3668 reflections	Δρ_min = −0.41 e Å⁻³
262 parameters

Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cu1	1.11111 (3)	0.47628 (3)	0.40624 (3)	0.03419 (11)
O11	0.99508 (16)	0.32526 (17)	0.43180 (19)	0.0499 (5)
O12	1.18983 (16)	0.63828 (16)	0.40754 (17)	0.0440 (4)
C11	0.8752 (2)	0.2967 (2)	0.5137 (2)	0.0369 (5)
C12	0.8048 (2)	0.1757 (2)	0.5189 (2)	0.0351 (5)
C13	0.8728 (3)	0.0988 (3)	0.4383 (3)	0.0492 (6)
H13	0.9618	0.1230	0.3800	0.059*
C14	0.8095 (3)	−0.0143 (3)	0.4433 (3)	0.0568 (7)
H14	0.8564	−0.0666	0.3897	0.068*
C15	0.6776 (3)	−0.0490 (3)	0.5274 (3)	0.0498 (7)
H15	0.6349	−0.1247	0.5306	0.060*
C16	0.6087 (3)	0.0279 (3)	0.6069 (3)	0.0470 (6)
H16	0.5191	0.0044	0.6637	0.056*
C17	0.6716 (2)	0.1398 (2)	0.6030 (2)	0.0408 (6)
H17	0.6243	0.1916	0.6572	0.049*
O21	1.02164 (17)	0.60977 (18)	0.25640 (18)	0.0495 (4)
O22	1.16461 (17)	0.35143 (16)	0.58557 (17)	0.0452 (4)
C21	0.9089 (2)	0.6714 (2)	0.2873 (2)	0.0370 (5)
C22	0.8591 (2)	0.7841 (2)	0.1645 (2)	0.0382 (5)
C23	0.7344 (3)	0.8541 (3)	0.1901 (3)	0.0535 (7)
H23	0.6771	0.8249	0.2837	0.064*
C24	0.6936 (3)	0.9660 (3)	0.0797 (3)	0.0694 (9)
H24	0.6096	1.0123	0.0993	0.083*
C25	0.7761 (4)	1.0094 (3)	−0.0586 (3)	0.0678 (9)
H25	0.7497	1.0866	−0.1329	0.081*
C26	0.8975 (3)	0.9385 (3)	−0.0869 (3)	0.0666 (8)
H26	0.9523	0.9660	−0.1815	0.080*
C27	0.9401 (3)	0.8263 (3)	0.0233 (3)	0.0540 (7)
H27	1.0232	0.7791	0.0026	0.065*
N31	1.28562 (19)	0.41356 (19)	0.25284 (19)	0.0354 (4)
N32	1.4763 (2)	0.2919 (2)	0.0746 (2)	0.0522 (6)
C31	1.2485 (3)	0.3591 (3)	0.1760 (3)	0.0457 (6)
H31	1.1554	0.3601	0.1804	0.055*
C32	1.3443 (3)	0.2991 (3)	0.0868 (3)	0.0519 (7)
H32	1.3115	0.2631	0.0344	0.062*
C33	1.5184 (2)	0.3494 (2)	0.1517 (3)	0.0443 (6)
C34	1.6606 (3)	0.3475 (3)	0.1428 (3)	0.0615 (8)
H34	1.7237	0.3059	0.0862	0.074*
C35	1.7047 (3)	0.4059 (3)	0.2163 (3)	0.0684 (9)
H35	1.7984	0.4048	0.2089	0.082*
C36	1.6121 (3)	0.4678 (3)	0.3030 (3)	0.0608 (8)
H36	1.6448	0.5078	0.3523	0.073*
C37	1.4736 (3)	0.4702 (3)	0.3163 (3)	0.0468 (6)
H37	1.4124	0.5106	0.3753	0.056*
C38	1.4240 (2)	0.4112 (2)	0.2406 (2)	0.0363 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.03083 (17)	0.03639 (17)	0.04054 (18)	−0.00078 (11)	−0.00605 (12)	−0.02234 (13)
O11	0.0379 (10)	0.0541 (11)	0.0676 (12)	−0.0115 (8)	0.0016 (9)	−0.0407 (9)
O12	0.0422 (10)	0.0443 (10)	0.0528 (10)	−0.0082 (8)	−0.0025 (8)	−0.0307 (8)
C11	0.0375 (14)	0.0357 (13)	0.0414 (13)	−0.0001 (11)	−0.0138 (12)	−0.0168 (11)
C12	0.0380 (13)	0.0327 (12)	0.0396 (13)	−0.0006 (10)	−0.0150 (11)	−0.0159 (10)
C13	0.0387 (14)	0.0505 (15)	0.0651 (17)	−0.0080 (12)	−0.0026 (13)	−0.0344 (14)
C14	0.0577 (18)	0.0534 (17)	0.0745 (19)	−0.0017 (14)	−0.0120 (15)	−0.0430 (15)
C15	0.0589 (18)	0.0380 (14)	0.0593 (16)	−0.0103 (12)	−0.0237 (14)	−0.0174 (12)
C16	0.0423 (15)	0.0473 (15)	0.0485 (15)	−0.0119 (12)	−0.0099 (12)	−0.0141 (12)
C17	0.0433 (14)	0.0411 (14)	0.0403 (13)	−0.0041 (11)	−0.0112 (11)	−0.0172 (11)
O21	0.0420 (10)	0.0636 (11)	0.0481 (10)	0.0139 (9)	−0.0157 (8)	−0.0291 (9)
O22	0.0435 (10)	0.0467 (10)	0.0421 (10)	0.0063 (8)	−0.0103 (8)	−0.0171 (8)
C21	0.0380 (14)	0.0378 (13)	0.0463 (14)	−0.0037 (11)	−0.0137 (12)	−0.0246 (11)
C22	0.0433 (14)	0.0392 (13)	0.0408 (13)	−0.0027 (11)	−0.0134 (11)	−0.0220 (11)
C23	0.0600 (18)	0.0604 (17)	0.0413 (14)	0.0139 (14)	−0.0151 (13)	−0.0246 (13)
C24	0.089 (2)	0.067 (2)	0.0587 (19)	0.0328 (18)	−0.0347 (18)	−0.0315 (16)
C25	0.100 (3)	0.0545 (18)	0.0569 (19)	0.0055 (18)	−0.0405 (19)	−0.0190 (15)
C26	0.081 (2)	0.076 (2)	0.0396 (16)	−0.0212 (18)	−0.0102 (16)	−0.0173 (15)
C27	0.0476 (16)	0.0667 (19)	0.0508 (16)	−0.0041 (14)	−0.0096 (14)	−0.0275 (14)
N31	0.0364 (11)	0.0353 (10)	0.0357 (10)	−0.0006 (8)	−0.0072 (9)	−0.0169 (9)
N32	0.0573 (15)	0.0457 (13)	0.0505 (13)	0.0041 (11)	−0.0010 (11)	−0.0263 (11)
C31	0.0421 (15)	0.0506 (15)	0.0452 (14)	−0.0046 (12)	−0.0048 (12)	−0.0230 (12)
C32	0.0621 (19)	0.0520 (16)	0.0474 (15)	−0.0075 (14)	−0.0044 (14)	−0.0299 (13)
C33	0.0401 (14)	0.0364 (13)	0.0419 (14)	0.0056 (11)	−0.0030 (12)	−0.0084 (11)
C34	0.0439 (16)	0.0628 (19)	0.0628 (19)	0.0138 (14)	−0.0055 (15)	−0.0205 (15)
C35	0.0355 (16)	0.084 (2)	0.065 (2)	0.0011 (15)	−0.0125 (15)	−0.0107 (17)
C36	0.0482 (17)	0.078 (2)	0.0540 (17)	−0.0079 (15)	−0.0188 (15)	−0.0183 (15)
C37	0.0422 (15)	0.0528 (16)	0.0447 (14)	−0.0024 (12)	−0.0100 (12)	−0.0189 (12)
C38	0.0356 (13)	0.0332 (12)	0.0331 (12)	0.0000 (10)	−0.0055 (10)	−0.0089 (10)

Geometric parameters (Å, º) top

Cu1—O12	1.9582 (15)	C23—C24	1.375 (3)
Cu1—O11	1.9660 (15)	C23—H23	0.9300
Cu1—O21	1.9735 (16)	C24—C25	1.367 (4)
Cu1—O22	1.9746 (16)	C24—H24	0.9300
Cu1—N31	2.2465 (18)	C25—C26	1.366 (4)
Cu1—Cu1ⁱ	2.6683 (6)	C25—H25	0.9300
O11—C11	1.258 (3)	C26—C27	1.383 (4)
O12—C11ⁱ	1.263 (2)	C26—H26	0.9300
C11—O12ⁱ	1.263 (2)	C27—H27	0.9300
C11—C12	1.498 (3)	N31—C31	1.313 (3)
C12—C13	1.377 (3)	N31—C38	1.370 (3)
C12—C17	1.383 (3)	N32—C32	1.302 (3)
C13—C14	1.383 (3)	N32—C33	1.366 (3)
C13—H13	0.9300	C31—C32	1.413 (3)
C14—C15	1.370 (4)	C31—H31	0.9300
C14—H14	0.9300	C32—H32	0.9300
C15—C16	1.371 (3)	C33—C34	1.415 (4)
C15—H15	0.9300	C33—C38	1.416 (3)
C16—C17	1.376 (3)	C34—C35	1.351 (4)
C16—H16	0.9300	C34—H34	0.9300
C17—H17	0.9300	C35—C36	1.395 (4)
O21—C21	1.255 (3)	C35—H35	0.9300
O22—C21ⁱ	1.267 (3)	C36—C37	1.369 (3)
C21—O22ⁱ	1.267 (3)	C36—H36	0.9300
C21—C22	1.500 (3)	C37—C38	1.407 (3)
C22—C23	1.381 (3)	C37—H37	0.9300
C22—C27	1.386 (3)

O12—Cu1—O11	167.30 (6)	C27—C22—C21	120.9 (2)
O12—Cu1—O21	89.25 (7)	C24—C23—C22	121.2 (3)
O11—Cu1—O21	88.44 (7)	C24—C23—H23	119.4
O12—Cu1—O22	89.63 (7)	C22—C23—H23	119.4
O11—Cu1—O22	89.93 (7)	C25—C24—C23	120.2 (3)
O21—Cu1—O22	167.48 (6)	C25—C24—H24	119.9
O12—Cu1—N31	101.20 (7)	C23—C24—H24	119.9
O11—Cu1—N31	91.45 (6)	C26—C25—C24	119.5 (3)
O21—Cu1—N31	95.59 (7)	C26—C25—H25	120.3
O22—Cu1—N31	96.86 (7)	C24—C25—H25	120.3
O12—Cu1—Cu1ⁱ	85.49 (5)	C25—C26—C27	120.9 (3)
O11—Cu1—Cu1ⁱ	81.87 (5)	C25—C26—H26	119.6
O21—Cu1—Cu1ⁱ	85.08 (5)	C27—C26—H26	119.6
O22—Cu1—Cu1ⁱ	82.40 (5)	C26—C27—C22	120.0 (3)
N31—Cu1—Cu1ⁱ	173.27 (5)	C26—C27—H27	120.0
C11—O11—Cu1	125.83 (15)	C22—C27—H27	120.0
C11ⁱ—O12—Cu1	121.79 (15)	C31—N31—C38	116.26 (19)
O11—C11—O12ⁱ	125.0 (2)	C31—N31—Cu1	115.16 (15)
O11—C11—C12	117.4 (2)	C38—N31—Cu1	128.20 (14)
O12ⁱ—C11—C12	117.6 (2)	C32—N32—C33	115.7 (2)
C13—C12—C17	119.0 (2)	N31—C31—C32	122.6 (2)
C13—C12—C11	119.8 (2)	N31—C31—H31	118.7
C17—C12—C11	121.1 (2)	C32—C31—H31	118.7
C12—C13—C14	120.4 (2)	N32—C32—C31	123.1 (2)
C12—C13—H13	119.8	N32—C32—H32	118.5
C14—C13—H13	119.8	C31—C32—H32	118.5
C15—C14—C13	120.0 (2)	N32—C33—C34	119.2 (2)
C15—C14—H14	120.0	N32—C33—C38	122.0 (2)
C13—C14—H14	120.0	C34—C33—C38	118.9 (2)
C14—C15—C16	120.0 (2)	C35—C34—C33	120.1 (3)
C14—C15—H15	120.0	C35—C34—H34	119.9
C16—C15—H15	120.0	C33—C34—H34	119.9
C15—C16—C17	120.3 (2)	C34—C35—C36	121.1 (3)
C15—C16—H16	119.9	C34—C35—H35	119.4
C17—C16—H16	119.9	C36—C35—H35	119.4
C16—C17—C12	120.3 (2)	C37—C36—C35	120.6 (3)
C16—C17—H17	119.8	C37—C36—H36	119.7
C12—C17—H17	119.8	C35—C36—H36	119.7
C21—O21—Cu1	122.18 (16)	C36—C37—C38	119.8 (2)
C21ⁱ—O22—Cu1	125.03 (15)	C36—C37—H37	120.1
O21—C21—O22ⁱ	125.1 (2)	C38—C37—H37	120.1
O21—C21—C22	117.6 (2)	N31—C38—C37	120.2 (2)
O22ⁱ—C21—C22	117.2 (2)	N31—C38—C33	120.3 (2)
C23—C22—C27	118.2 (2)	C37—C38—C33	119.4 (2)
C23—C22—C21	120.8 (2)

Symmetry code: (i) −x+2, −y+1, −z+1.

Experimental details

Crystal data
Chemical formula	[Cu₂(C₇H₅O₂)₄(C₈H₆N₂)₂]
M_r	871.82
Crystal system, space group	Triclinic, P1
Temperature (K)	293
a, b, c (Å)	10.1423 (16), 10.3400 (17), 10.5148 (17)
α, β, γ (°)	65.459 (2), 73.063 (3), 82.142 (3)
V (Å³)	959.4 (3)
Z	1
Radiation type	Mo Kα
µ (mm⁻¹)	1.17
Crystal size (mm)	0.15 × 0.10 × 0.08

Data collection
Diffractometer	Bruker SMART CCD area-detector diffractometer
Absorption correction	–
No. of measured, independent and observed [I > 2σ(I)] reflections	5377, 3668, 2983
R_int	0.031
(sin θ/λ)_max (Å⁻¹)	0.617

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.033, 0.080, 0.96
No. of reflections	3668
No. of parameters	262
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.28, −0.41

Computer programs: SMART (Bruker, 1997), SAINT (Bruker, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 1998).

Acknowledgements

Financial support from the Environmental Technology Educational Innovation Program (2006) of the Ministry of the Environment is gratefully acknowledged.

References

Bruker (1997). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (1998). SHELXTL. Version 5.10. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Casarin, M., Corvaja, C., Nicola, C. D., Falcomer, D., Franco, L., Monari, M., Pandolfo, L., Pettinari, C. & Piccinelli, F. (2005). Inorg. Chem. 44, 6265–6276. Web of Science CSD CrossRef PubMed CAS Google Scholar
Cotton, F. A. & Walton, R. A. (1993). Multiple Bonds Between Metal Atoms, 2nd ed. New York: Oxford University Press. Google Scholar
Deka, K., Sarma, R. & Baruah, J. B. (2006). Inorg. Chem. Commun. 9, 931–934. Web of Science CSD CrossRef CAS Google Scholar
Goto, M., Furukawa, M., Miyamoto, J., Kanoh, H. & Kaneko, K. (2007). Langmuir, 23, 5264–5266. Web of Science CrossRef PubMed CAS Google Scholar
Pichon, A., Fierro, C. M., Nieuwenhuyzen, M. & James, L. (2007). CrystEngComm, 9, 449–451. Web of Science CSD CrossRef CAS Google Scholar
Sheldrick, G. M. (1997). SHELXL97 and SHELXS97. University of Göttingen, Germany. Google Scholar
Speier, G. & Fülöp, V. (1989). J. Chem. Soc. Dalton Trans. pp. 2331–2333. CSD CrossRef Web of Science Google Scholar
Takamizawa, S., Nakata, E. & Saito, T. (2004). Inorg. Chem. Commun. 7, 1–3. Web of Science CSD CrossRef CAS Google Scholar