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Acta Cryst. (2007). E63, m2255    [ doi:10.1107/S1600536807037129 ]

Bis{methyl [1-(6-acetyl-2-pyridyl)ethylidene]hydrazinecarbodithioato}nickel(II)

M. Akbar Ali, A. H. Mirza and P. V. Bernhardt

Abstract top

The title compound, [Ni(C11H12N3OS2)2], is a six-coordinate NiII complex that is similar to other bis-tridentate N,N',S-coordinated Schiff bases, but in this case an acetyl substituent adjacent to the coordinated pyridyl N atom elongates the Ni-N bond by more than 0.06 Å relative to the complex where no substituent is present. A related 6-methyl-substituted Ni complex also shows a similar Ni-N bond elongation.

Comment top

The potentially pentadendate Schiff base ligand (I) and its close relatives have been shown to favour pentagonal bipyramidal structures when complexed with metals such Sn(IV) (Akbar Ali et al., 2004), Zn(II) and Cd(II) (Akbar Ali, Mirza, Voo et al., 2003). In the synthesis of (I) it has been reported that the intermediate one-armed analogue (II) is also a product of the condensation reaction between 2,6-diacetylpyridine and S-methyldithiocarbate (Akbar Ali, Mirza, Keng & Butcher, 2003). The Pd(II) complex of (II) was structurally characterized. Herein we report the crystal structure of the bis-ligated six-coordinate NiII complex (III).

The structure of (III) reveals a distorted octahedral coordination geometry (Fig. 1). Each ligand deprotonates at N1a/b and the C1a/b-N1/a/b bonds approach double bond order due to the preferred ene-thiolate form of the coordinated monoanionic ligand (Table 2). The ligands each bind as a tridentate N,N,S chelate and the planar nature of the ligand enforces a meridional coordination mode. The shortest bond lengths are the central Ni—N bonds as expected. A point of interest is the rather long Ni—N3a/b bonds in comparison with the homologous complex (IV) (av. 2.12 Å) which lacks any substituents on the 6-positions of its pyridyl rings (Su et al., 1998). In this case the Ni—N bond lengths are more than 0.06 Å longer than found in the structure of (IV). Steric interactions between the non-coordinating acetyl groups and the adjacent ligand result in this bond elongation. The structure of the 6-methyl substituted analog (V) also exhibits a similar lengthening of the Ni—Npyr coordinate bonds (Akbar Ali et al., 1997). It is also notable that these coordinate bond distortions are localized at the pyridyl groups as the remaining Ni—N and Ni—S coordinate bonds are the same within experimental error as those reported for (IV).

In conclusion, the absence of a second chelating arm in the ligand (II) leads to a preferred bis-tridentate coordination mode in complex with NiII and the 6-acetyl substituents on the pyridyl rings play a role in lengthening the Ni—Npyr bonds substantially.

Related literature top

For related literature, see: Akbar Ali, Mahbub-ul-Haque Majumder, Butcher, Jasinski & Jasinski (1997); Akbar Ali, Mirza, Keng & Butcher (2003); Akbar Ali, Mirza, Tan, Wei & Bernhardt (2004); Akbar Ali, Mirza, Voo, Tan & Bernhardt (2003); Su et al. (1998).

Experimental top

To a solution of nickel(II) chloride hexahydrate (0.03 g; 1.25 x 10 −4 mol) in boiling methanol (20 ml), conc. HCl (ca 0.3 ml) was added. The solution was mixed with a hot solution of the Schiff base, 2,6-diacetylpyridinebis(S-methyldithiocarbazonate, (I)) (0.09 g; 2.5 x 10 −4 mol) in methanol (50 ml) and the mixture was heated on a water bath for about one minute. On standing, the reaction mixture deposited crystals of the complex which were filtered off, washed with methanol and dried in a desiccator over anhydrous silica gel. Hydrolysis of (I) to (II) during the reaction was confirmed by isolation of its NiII complex (III).

Refinement top

All H atoms were treated as riding with C—H distances ranging from 0.93 to 0.96 Å and Uiso(H) values equal to 1.5 (methyl H atoms) or 1.2 (all other atoms) times Ueq of the parent atom. Only a unique (octant) data set was measured for the orthorhombic system so the Rint value is undetermined. Also the Flack parameter is only nominal given the lack of Friedel pairs in the data set.

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Version 1.64.02; Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. ORTEP-3 plot of (III) (30% probability ellipsoids). H-atoms have been omitted for clarity. Atom labelling on ligand B follows that shown on ligand A.
[Figure 2] Fig. 2. The structures of compounds (I)–(V).
Bis{methyl [1-(6-acetyl-2-pyridyl)ethylidene]hydrazinecarbodithioato}nickel(II) top
Crystal data top
[Ni(C11H12N3O1S2)2]F000 = 1224
Mr = 591.42Dx = 1.51 Mg m−3
Orthorhombic, P212121Mo Kα radiation
λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 25 reflections
a = 10.6343 (8) Åθ = 11.5–13.5º
b = 10.8217 (7) ŵ = 1.10 mm−1
c = 22.603 (2) ÅT = 293 (2) K
V = 2601.2 (3) Å3Prism, brown
Z = 40.6 × 0.6 × 0.3 mm
Data collection top
Enraf–Nonius CAD-4
diffractometer		Rint = 0
Monochromator: graphiteθmax = 25.0º
T = 293(2) Kθmin = 1.8º
non–profiled ω/2θ scansh = 0→12
Absorption correction: ψ scan
(North et al., 1968)		k = 0→12
Tmin = 0.558, Tmax = 0.734l = 0→26
2601 measured reflections3 standard reflections
2601 independent reflections every 120 min
2197 reflections with I > 2σ(I) intensity decay: 1%
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-atom parameters constrained
R[F2 > 2σ(F2)] = 0.027  w = 1/[σ2(Fo2) + (0.0488P)2 + 0.1306P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.075(Δ/σ)max < 0.001
S = 1.05Δρmax = 0.36 e Å−3
2601 reflectionsΔρmin = −0.23 e Å−3
316 parametersExtinction correction: none
Primary atom site location: structure-invariant direct methodsAbsolute structure: Flack (1983), with how many Friedel pairs?
Secondary atom site location: difference Fourier mapFlack parameter: 0.032 (17)
Crystal data top
[Ni(C11H12N3O1S2)2]V = 2601.2 (3) Å3
Mr = 591.42Z = 4
Orthorhombic, P212121Mo Kα
a = 10.6343 (8) ŵ = 1.10 mm−1
b = 10.8217 (7) ÅT = 293 (2) K
c = 22.603 (2) Å0.6 × 0.6 × 0.3 mm
Data collection top
Enraf–Nonius CAD-4
diffractometer		2197 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)		Rint = 0
Tmin = 0.558, Tmax = 0.7343 standard reflections
2601 measured reflections every 120 min
2601 independent reflections intensity decay: 1%
Refinement top
R[F2 > 2σ(F2)] = 0.027H-atom parameters constrained
wR(F2) = 0.075Δρmax = 0.36 e Å−3
S = 1.05Δρmin = −0.23 e Å−3
2601 reflectionsAbsolute structure: Flack (1983), with how many Friedel pairs?
316 parametersFlack parameter: 0.032 (17)
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 > 2sigma(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
xyzUiso*/Ueq
Ni10.73584 (4)0.93441 (4)0.12063 (2)0.03305 (14)
C1A0.7000 (4)0.7464 (4)0.21782 (18)0.0388 (9)
C1B0.5642 (4)0.9426 (4)0.01415 (17)0.0409 (9)
C2A0.6984 (6)0.6758 (5)0.33646 (19)0.0660 (15)
H2A10.69930.60940.36460.099*
H2A20.62350.72410.34170.099*
H2A30.77090.72730.34240.099*
C2B0.5101 (5)0.9472 (6)−0.10626 (19)0.0710 (15)
H2B10.4470.9499−0.13660.107*
H2B20.55950.8735−0.11070.107*
H2B30.56361.0183−0.10960.107*
C3A0.6694 (4)1.0590 (4)0.22846 (16)0.0376 (9)
C3B0.8810 (4)0.9067 (4)0.01403 (19)0.0424 (10)
C4A0.6422 (5)1.0822 (4)0.29212 (17)0.0531 (11)
H4A10.63891.00490.31290.08*
H4A20.56291.12370.29580.08*
H4A30.70741.13290.30870.08*
C4B0.9165 (5)0.8986 (5)−0.05007 (18)0.0612 (14)
H4B10.84240.9058−0.0740.092*
H4B20.95630.8205−0.05760.092*
H4B30.97370.9643−0.05960.092*
C5A0.6787 (4)1.1619 (4)0.18649 (19)0.0380 (9)
C5B0.9791 (4)0.8978 (4)0.06058 (19)0.0400 (10)
C6A0.6311 (4)1.2788 (4)0.1985 (2)0.0475 (11)
H6A0.59371.29540.23490.057*
C6B1.1035 (4)0.8744 (5)0.0466 (2)0.0545 (12)
H6B1.12790.86580.00730.065*
C7A0.6397 (5)1.3698 (4)0.1562 (2)0.0573 (12)
H7A0.60521.44740.16310.069*
C7B1.1902 (4)0.8640 (5)0.0910 (2)0.0605 (13)
H7B1.27410.84790.08250.073*
C8A0.6995 (5)1.3451 (4)0.1041 (2)0.0542 (12)
H8A0.70581.40550.07490.065*
C8B1.1505 (4)0.8780 (4)0.1483 (2)0.0578 (13)
H8B1.20740.86970.17930.069*
C9A0.7504 (4)1.2290 (4)0.09532 (18)0.0442 (9)
C9B1.0268 (4)0.9041 (4)0.15966 (19)0.0432 (10)
C10A0.8309 (6)1.2056 (4)0.0410 (2)0.0630 (14)
C10B0.9866 (4)0.9276 (4)0.22341 (19)0.0481 (10)
C11A0.7768 (8)1.2393 (6)−0.0167 (2)0.103 (3)
H11D0.83641.2215−0.04750.155*
H11E0.75711.3258−0.0170.155*
H11F0.70141.1924−0.02330.155*
C11B1.0123 (6)0.8259 (5)0.2656 (2)0.0741 (16)
H11A0.98430.84940.30440.111*
H11B1.1010.80940.26660.111*
H11C0.96830.75290.25320.111*
N1A0.6847 (3)0.8516 (3)0.24452 (15)0.0412 (8)
N1B0.6739 (3)0.9282 (3)−0.00883 (13)0.0403 (7)
N2A0.6903 (3)0.9504 (3)0.20621 (13)0.0355 (7)
N2B0.7690 (3)0.9214 (3)0.03321 (13)0.0361 (7)
N3A0.7383 (3)1.1368 (3)0.13456 (13)0.0353 (7)
N3B0.9405 (3)0.9159 (3)0.11689 (15)0.0378 (7)
S1A0.71898 (12)0.71710 (10)0.14389 (5)0.0465 (3)
S1B0.52284 (9)0.95535 (12)0.08710 (4)0.0471 (3)
S2A0.70145 (14)0.61389 (11)0.26300 (5)0.0592 (3)
S2B0.43594 (11)0.94696 (14)−0.03511 (5)0.0573 (3)
O1A0.9365 (4)1.1685 (4)0.04757 (19)0.0833 (13)
O1B0.9389 (3)1.0233 (3)0.23694 (15)0.0592 (9)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ni10.0334 (2)0.0345 (2)0.0312 (2)−0.0014 (2)0.0013 (2)−0.0021 (2)
C1A0.036 (2)0.037 (2)0.044 (2)−0.0014 (18)−0.0042 (18)0.0084 (18)
C1B0.046 (2)0.033 (2)0.044 (2)0.001 (2)−0.0068 (18)−0.003 (2)
C2A0.092 (4)0.063 (3)0.043 (3)−0.003 (3)0.003 (3)0.012 (2)
C2B0.075 (3)0.096 (4)0.042 (2)−0.009 (3)−0.010 (2)0.009 (3)
C3A0.0350 (19)0.040 (2)0.0376 (19)−0.003 (2)0.0012 (16)−0.0049 (19)
C3B0.046 (2)0.038 (2)0.044 (2)−0.0020 (19)0.0095 (19)−0.0023 (19)
C4A0.068 (3)0.052 (3)0.039 (2)−0.004 (3)0.007 (2)−0.007 (2)
C4B0.057 (3)0.084 (4)0.043 (2)0.004 (3)0.015 (2)−0.004 (2)
C5A0.035 (2)0.034 (2)0.045 (2)−0.0054 (17)−0.006 (2)−0.0063 (18)
C5B0.038 (2)0.033 (2)0.049 (2)−0.0027 (17)0.0031 (19)−0.0017 (18)
C6A0.049 (3)0.039 (2)0.054 (3)0.002 (2)0.006 (2)−0.013 (2)
C6B0.037 (2)0.053 (3)0.073 (3)−0.004 (2)0.012 (2)−0.006 (3)
C7A0.061 (3)0.032 (2)0.079 (3)0.005 (2)0.002 (3)−0.004 (2)
C7B0.028 (2)0.058 (3)0.095 (4)0.002 (2)0.004 (2)−0.011 (3)
C8A0.062 (3)0.033 (2)0.067 (3)0.000 (2)0.005 (2)0.010 (2)
C8B0.034 (2)0.053 (3)0.086 (3)0.002 (2)−0.016 (2)−0.010 (3)
C9A0.045 (2)0.040 (2)0.048 (2)−0.005 (2)−0.001 (2)0.0049 (18)
C9B0.038 (2)0.034 (2)0.058 (3)−0.0058 (18)−0.006 (2)−0.0061 (19)
C10A0.097 (4)0.033 (2)0.060 (3)−0.009 (3)0.023 (3)0.007 (2)
C10B0.039 (2)0.051 (3)0.054 (2)−0.004 (2)−0.0140 (19)−0.011 (2)
C11A0.172 (8)0.086 (4)0.052 (3)−0.007 (5)0.020 (4)0.009 (3)
C11B0.083 (4)0.074 (4)0.065 (4)0.011 (3)−0.013 (3)0.006 (3)
N1A0.0463 (19)0.0378 (19)0.0394 (18)−0.0045 (16)0.0008 (16)0.0074 (16)
N1B0.0421 (18)0.0453 (19)0.0336 (16)0.0015 (18)−0.0038 (14)0.0003 (17)
N2A0.0364 (17)0.0354 (18)0.0347 (16)−0.0019 (15)−0.0012 (13)0.0003 (14)
N2B0.0364 (16)0.0369 (17)0.0351 (15)0.0005 (17)0.0048 (15)−0.0003 (14)
N3A0.0354 (17)0.0336 (16)0.0367 (17)0.0007 (15)0.0030 (15)0.0003 (13)
N3B0.0317 (15)0.0347 (18)0.0470 (18)−0.0014 (14)−0.0029 (15)−0.0028 (17)
S1A0.0627 (7)0.0349 (5)0.0417 (5)−0.0032 (5)0.0036 (5)−0.0027 (4)
S1B0.0327 (5)0.0656 (8)0.0428 (5)−0.0014 (5)0.0003 (4)−0.0091 (6)
S2A0.0878 (9)0.0398 (6)0.0500 (7)−0.0036 (6)−0.0048 (6)0.0104 (5)
S2B0.0481 (6)0.0739 (9)0.0499 (6)0.0051 (7)−0.0147 (5)−0.0001 (7)
O1A0.086 (3)0.065 (3)0.098 (3)0.009 (2)0.048 (3)0.013 (2)
O1B0.058 (2)0.0513 (19)0.069 (2)0.0038 (17)−0.0120 (17)−0.0159 (17)
Geometric parameters (Å, °) top
Ni1—N2A2.002 (3)C5A—N3A1.361 (5)
Ni1—N2B2.012 (3)C5A—C6A1.390 (6)
Ni1—N3B2.188 (3)C5B—N3B1.351 (5)
Ni1—N3A2.213 (3)C5B—C6B1.383 (6)
Ni1—S1B2.399 (1)C6A—C7A1.375 (6)
Ni1—S1A2.416 (1)C6A—H6A0.93
C1A—N1A1.299 (5)C6B—C7B1.368 (7)
C1A—S1A1.713 (4)C6B—H6B0.93
C1A—S2A1.760 (4)C7A—C8A1.366 (6)
C1B—N1B1.286 (5)C7A—H7A0.93
C1B—S1B1.712 (4)C7B—C8B1.370 (7)
C1B—S2B1.761 (4)C7B—H7B0.93
C2A—S2A1.791 (5)C8A—C9A1.382 (6)
C2A—H2A10.96C8A—H8A0.93
C2A—H2A20.96C8B—C9B1.371 (6)
C2A—H2A30.96C8B—H8B0.93
C2B—S2B1.791 (5)C9A—N3A1.342 (5)
C2B—H2B10.96C9A—C10A1.518 (7)
C2B—H2B20.96C9B—N3B1.338 (5)
C2B—H2B30.96C9B—C10B1.524 (6)
C3A—N2A1.297 (5)C10A—O1A1.201 (7)
C3A—C5A1.466 (6)C10A—C11A1.473 (8)
C3A—C4A1.489 (5)C10B—O1B1.193 (5)
C3B—N2B1.277 (5)C10B—C11B1.482 (6)
C3B—C5B1.485 (6)C11A—H11D0.96
C3B—C4B1.500 (5)C11A—H11E0.96
C4A—H4A10.96C11A—H11F0.96
C4A—H4A20.96C11B—H11A0.96
C4A—H4A30.96C11B—H11B0.96
C4B—H4B10.96C11B—H11C0.96
C4B—H4B20.96N1A—N2A1.377 (4)
C4B—H4B30.96N1B—N2B1.390 (4)
N2A—Ni1—N2B176.0 (1)C5A—C6A—H6A120.3
N2A—Ni1—N3B106.6 (1)C7B—C6B—C5B119.4 (5)
N2B—Ni1—N3B77.4 (1)C7B—C6B—H6B120.3
N2A—Ni1—N3A77.3 (1)C5B—C6B—H6B120.3
N2B—Ni1—N3A102.0 (1)C8A—C7A—C6A119.4 (4)
N3B—Ni1—N3A94.8 (1)C8A—C7A—H7A120.3
N2A—Ni1—S1B93.92 (9)C6A—C7A—H7A120.3
N2B—Ni1—S1B82.07 (9)C6B—C7B—C8B118.5 (4)
N3B—Ni1—S1B159.4 (1)C6B—C7B—H7B120.7
N3A—Ni1—S1B87.85 (9)C8B—C7B—H7B120.7
N2A—Ni1—S1A81.7 (1)C7A—C8A—C9A118.9 (4)
N2B—Ni1—S1A99.12 (9)C7A—C8A—H8A120.5
N3B—Ni1—S1A89.61 (9)C9A—C8A—H8A120.5
N3A—Ni1—S1A158.93 (8)C7B—C8B—C9B119.7 (4)
S1B—Ni1—S1A95.20 (5)C7B—C8B—H8B120.2
N1A—C1A—S1A129.0 (3)C9B—C8B—H8B120.2
N1A—C1A—S2A116.5 (3)N3A—C9A—C8A123.0 (4)
S1A—C1A—S2A114.5 (2)N3A—C9A—C10A117.7 (4)
N1B—C1B—S1B129.2 (3)C8A—C9A—C10A119.3 (4)
N1B—C1B—S2B116.8 (3)N3B—C9B—C8B122.8 (4)
S1B—C1B—S2B114.1 (2)N3B—C9B—C10B118.4 (3)
S2A—C2A—H2A1109.5C8B—C9B—C10B118.7 (4)
S2A—C2A—H2A2109.5O1A—C10A—C11A123.9 (6)
H2A1—C2A—H2A2109.5O1A—C10A—C9A118.9 (5)
S2A—C2A—H2A3109.5C11A—C10A—C9A117.0 (5)
H2A1—C2A—H2A3109.5O1B—C10B—C11B123.9 (4)
H2A2—C2A—H2A3109.5O1B—C10B—C9B120.4 (4)
S2B—C2B—H2B1109.5C11B—C10B—C9B115.7 (4)
S2B—C2B—H2B2109.5C10A—C11A—H11D109.5
H2B1—C2B—H2B2109.5C10A—C11A—H11E109.5
S2B—C2B—H2B3109.5H11D—C11A—H11E109.5
H2B1—C2B—H2B3109.5C10A—C11A—H11F109.5
H2B2—C2B—H2B3109.5H11D—C11A—H11F109.5
N2A—C3A—C5A115.2 (3)H11E—C11A—H11F109.5
N2A—C3A—C4A124.1 (4)C10B—C11B—H11A109.5
C5A—C3A—C4A120.7 (4)C10B—C11B—H11B109.5
N2B—C3B—C5B115.0 (4)H11A—C11B—H11B109.5
N2B—C3B—C4B124.8 (4)C10B—C11B—H11C109.5
C5B—C3B—C4B120.2 (4)H11A—C11B—H11C109.5
C3A—C4A—H4A1109.5H11B—C11B—H11C109.5
C3A—C4A—H4A2109.5C1A—N1A—N2A112.5 (3)
H4A1—C4A—H4A2109.5C1B—N1B—N2B113.0 (3)
C3A—C4A—H4A3109.5C3A—N2A—N1A116.9 (3)
H4A1—C4A—H4A3109.5C3A—N2A—Ni1119.6 (3)
H4A2—C4A—H4A3109.5N1A—N2A—Ni1123.4 (2)
C3B—C4B—H4B1109.5C3B—N2B—N1B117.0 (3)
C3B—C4B—H4B2109.5C3B—N2B—Ni1120.4 (3)
H4B1—C4B—H4B2109.5N1B—N2B—Ni1122.7 (2)
C3B—C4B—H4B3109.5C9A—N3A—C5A117.8 (3)
H4B1—C4B—H4B3109.5C9A—N3A—Ni1130.1 (3)
H4B2—C4B—H4B3109.5C5A—N3A—Ni1108.4 (2)
N3A—C5A—C6A121.3 (4)C9B—N3B—C5B117.3 (3)
N3A—C5A—C3A115.9 (3)C9B—N3B—Ni1131.5 (3)
C6A—C5A—C3A122.7 (4)C5B—N3B—Ni1110.6 (3)
N3B—C5B—C6B122.2 (4)C1A—S1A—Ni192.36 (14)
N3B—C5B—C3B116.4 (3)C1B—S1B—Ni193.10 (14)
C6B—C5B—C3B121.4 (4)C1A—S2A—C2A103.5 (2)
C7A—C6A—C5A119.4 (4)C1B—S2B—C2B103.1 (2)
C7A—C6A—H6A120.3
Acknowledgements top

Support from the Australian Research Council and the University of Queensland is gratefully acknowledged.

references
References top

Akbar Ali, M., Mahbub-ul-Haque Majumder, S. M., Butcher, R. J., Jasinski, J. P. & Jasinski, J. M. (1997). Polyhedron, 16, 2749–2754.

Akbar Ali, M., Mirza, A. H., Keng, S. T. W. & Butcher, R. J. (2003). Transition Met. Chem. 28, 241–245.

Akbar Ali, M., Mirza, A. H., Tan, A. L., Wei, L. K. & Bernhardt, P. V. (2004). Polyhedron, 23, 2037–2043.

Akbar Ali, M., Mirza, A. H., Voo, C. W., Tan, A. L. & Bernhardt, P. V. (2003). Polyhedron, 22, 3433–3438.

Enraf–Nonius (1994). CAD-4 EXPRESS. Version 5.1/1.2. Enraf–Nonius, Delft, The Netherlands.

Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565–?.

Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.

Flack, H. D. (1983). Acta Cryst. A39, 876–881.

Harms, K. & Wocadlo, S. (1995). XCAD4. University of Marburg, Germany.

North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359.

Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.

Su, C.-Y., Zhang, Z.-F., Zhou, Q., Yang, X.-P., Wang, L.-G. & Kang, B.-S. (1998). J. Chem. Crystallogr. 28, 871–874.