supplementary materials


HTML versionpdf versioncif file3d viewstructure factorssupplementary materialsCIF check reportsimilar papers Open access

bt5260 scheme

Acta Cryst. (2010). E66, m620    [ doi:10.1107/S1600536810016041 ]

{3,3',5,5'-Tetramethoxy-2,2'-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}nickel(II)

G. E. Assey, R. J. Butcher and Y. Gultneh

Abstract top

The title square-planar nickel complex, [Ni(C20H22N2O6)], has Ni-N and Ni-O bond lengths of 1.8448 (14)/1.8478 (14) and 1.8536 (12)/1.8520 (12) Å. There is a slight twist in the two benzene rings at each end of the complex [dihedral angle = 11.11 (5)°]. All the atoms of the methoxy substitutents are in the plane of the ring to which they are attached except for one which deviates slightly [0.365 (3) Å]. In the crystal, weak C-H...O intermolecular interactions connect the molecules.

Comment top

Complexes of Ni(II) with N2O2 Schiff bases derived from salicylaldehyde have been studied for a long time as homogeneous catalysts due to their high activity and selectivity (Silva et al. 2002, Santos et al. 2000). These types of complexes have been described in the literature as catalytically active in oxidation and reduction reactions both as homogeneous and heterogeneous catalysts (Yoon & Burrows, 1988). Other areas where coordination chemistry has found application are in the areas of molecular adsorption, liquid-liquid extraction, ion exchange and metalloenzymes. They have been designed as potential transition metal host systems in host-guest chemistry in the similar way to that of enzyme substrate.

The importance of nickel salen complexes with aromatic substituents range from biological (Bal and Ülküseven, 2004), activation of O2 under very mild conditions (Soto-Garrodo, & Salas-Reyes, 2000) and mesogenic properties of substituted complexes. (Blake et al. 1995) reported metallomesogens based on nickel alkyl and alkoxy substituted salen.

The central Ni is in a square planar coordination environment of O1 O2, N1 and N2 with rms deviation of 0.0461 (6) Å (deviation from plane for Ni of 0.0034 (7) Å). The Ni—N and Ni—O bond distances are in the normal range for Ni-salen type complexes (Allen et al., 1987) at 1.8448 (14), and 1.8478 (14) Å for Ni—N and 1.8536 (12) Å and 1.8520 (12) Å for Ni—O. There is a slight twist in the two phenyl rings at each end of the complex (dihedral angle of 11.11 (5)°. All the atoms of the methoxy substitutents are in the plane of the ring to which they are attached except C19 which deviates slightly (0.365 (3) °). There are weak C—H···O intermolecular interactions connecting the molecules in the solid state.

Related literature top

For nickel–salen complexes with aromatic substituents, see: Bal & Ülküseven (2004). For their activation of O2, see: Soto-Garrodo & Salas-Reyes (2000); For their catalytic activity: Silva et al. (2002); Santos et al. (2000); Yoon & Burrows (1988). For the mesogenic properties of substituted complexes, see: Blake et al. (1995). For bond-length data, see: Allen et al. (1987).

Experimental top

The ligand synthesis was accomplished by adding a solution of (2 g, 33.3 mmol) ethylenediamine in 25 mls of methanol to a solution of (12.13 g, 66.6 mmol) 4,6-dimethoxysalicylaldehyde in 40 ml of methanol. The mixture was refluxed overnight while stirring. Then the mixture was evaporated under reduced pressure to afford yellow solids.

The complex was synthesized by mixing a solution of (0.38 g, 1 mmol) N,N-ethylenebis(4,6-dimethoxysalicylaldimine) in 5 ml of CH2Cl2 with a solution of (0.29 g, 1 mmol) nickel nitrate hexahydrate in 5 ml methanol. The solution mixture was stirred for 1 hour then filtered and layered with diethyl ether for crystallization. Single crystals of X-ray quality were obtained.

Refinement top

H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with a C—H distances of 0.95 and 0.99 Å Uiso(H) = 1.2Ueq(C) and 0.98 Å for CH3 [Uiso(H) = 1.5Ueq(C)].

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2007); cell refinement: CrysAlis PRO (Oxford Diffraction, 2007); data reduction: CrysAlis PRO (Oxford Diffraction, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Diagram of the square planar nickel complex C20H22N2NiO6 showing atom labeling.
[Figure 2] Fig. 2. The molecular packing for C20H22N2NiO6 viewed down the a axis.
{3,3',5,5'-Tetramethoxy-2,2'-[ethane-1,2- diylbis(nitrilomethylidyne)]diphenolato}nickel(II) top
Crystal data top
[Ni(C20H22N2O6)]F(000) = 928
Mr = 445.11Dx = 1.617 Mg m−3
Monoclinic, P21/cCu Kα radiation, λ = 1.54184 Å
Hall symbol: -P 2ybcCell parameters from 5663 reflections
a = 7.41599 (12) Åθ = 5.6–74.0°
b = 15.6945 (2) ŵ = 1.91 mm−1
c = 15.7203 (2) ÅT = 110 K
β = 91.9153 (13)°Needle, red
V = 1828.67 (5) Å30.53 × 0.15 × 0.12 mm
Z = 4
Data collection top
Oxford Diffraction Xcalibur Ruby Gemini
diffractometer		3603 independent reflections
Radiation source: Enhance (Cu) X-ray Source3370 reflections with I > 2σ(I)
graphiteRint = 0.022
Detector resolution: 10.5081 pixels mm-1θmax = 74.2°, θmin = 5.6°
ω scansh = −9→8
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2007)		k = −11→19
Tmin = 0.602, Tmax = 1.000l = −18→19
6746 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.036Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.098H-atom parameters constrained
S = 1.04 w = 1/[σ2(Fo2) + (0.0641P)2 + 1.0294P]
where P = (Fo2 + 2Fc2)/3
3603 reflections(Δ/σ)max < 0.001
266 parametersΔρmax = 0.42 e Å−3
0 restraintsΔρmin = −0.47 e Å−3
Crystal data top
[Ni(C20H22N2O6)]V = 1828.67 (5) Å3
Mr = 445.11Z = 4
Monoclinic, P21/cCu Kα radiation
a = 7.41599 (12) ŵ = 1.91 mm−1
b = 15.6945 (2) ÅT = 110 K
c = 15.7203 (2) Å0.53 × 0.15 × 0.12 mm
β = 91.9153 (13)°
Data collection top
Oxford Diffraction Xcalibur Ruby Gemini
diffractometer		3603 independent reflections
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2007)		3370 reflections with I > 2σ(I)
Tmin = 0.602, Tmax = 1.000Rint = 0.022
6746 measured reflectionsθmax = 74.2°
Refinement top
R[F2 > 2σ(F2)] = 0.036H-atom parameters constrained
wR(F2) = 0.098Δρmax = 0.42 e Å−3
S = 1.04Δρmin = −0.47 e Å−3
3603 reflectionsAbsolute structure: ?
266 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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
xyzUiso*/Ueq
Ni0.25525 (4)0.522587 (16)0.436449 (16)0.01249 (11)
O10.25637 (17)0.49637 (8)0.32150 (7)0.0166 (2)
O20.25493 (17)0.63580 (7)0.40321 (7)0.0168 (2)
O30.36236 (18)0.33461 (8)0.07279 (8)0.0209 (3)
O40.45100 (16)0.20821 (7)0.34353 (7)0.0183 (3)
O50.10218 (18)0.76296 (8)0.66590 (7)0.0192 (3)
O60.13141 (19)0.93215 (8)0.41651 (8)0.0230 (3)
N10.26710 (19)0.41000 (9)0.46989 (8)0.0143 (3)
N20.24084 (18)0.54755 (10)0.55089 (9)0.0145 (3)
C10.3028 (2)0.42368 (10)0.28756 (10)0.0142 (3)
C20.3067 (2)0.41965 (10)0.19756 (10)0.0158 (3)
H2A0.27430.46820.16430.019*
C30.3576 (2)0.34513 (11)0.15833 (10)0.0163 (3)
C40.4124 (2)0.27279 (11)0.20515 (11)0.0171 (3)
H4A0.45390.22330.17710.020*
C50.4047 (2)0.27513 (10)0.29228 (11)0.0150 (3)
C60.3462 (2)0.34938 (10)0.33579 (11)0.0152 (3)
C70.3154 (2)0.34535 (10)0.42475 (11)0.0145 (3)
H7A0.33130.29200.45260.017*
C80.2141 (2)0.39623 (11)0.55814 (10)0.0164 (3)
H8A0.27320.34450.58200.020*
H8B0.08180.38910.56050.020*
C90.2745 (2)0.47426 (10)0.60768 (11)0.0171 (3)
H9A0.20510.48010.66010.020*
H9B0.40440.47020.62390.020*
C100.2071 (2)0.62123 (11)0.58443 (10)0.0155 (3)
H10A0.19730.62390.64450.019*
C110.1837 (2)0.69804 (11)0.53782 (10)0.0155 (3)
C120.1328 (2)0.77404 (11)0.58121 (10)0.0165 (3)
C130.1162 (2)0.85044 (11)0.53987 (11)0.0188 (3)
H13A0.08310.90050.56950.023*
C140.1498 (2)0.85285 (11)0.45184 (11)0.0171 (3)
C150.1950 (2)0.78148 (11)0.40677 (10)0.0165 (3)
H15A0.21380.78530.34740.020*
C160.2134 (2)0.70230 (10)0.44895 (10)0.0144 (3)
C170.3271 (3)0.40816 (12)0.02106 (11)0.0264 (4)
H17A0.33330.3925−0.03910.040*
H17B0.41740.45210.03470.040*
H17C0.20650.43020.03220.040*
C180.5069 (3)0.13184 (11)0.30218 (12)0.0213 (4)
H18A0.54850.09030.34510.032*
H18B0.60560.14500.26430.032*
H18C0.40500.10800.26880.032*
C190.0109 (2)0.83006 (11)0.70858 (11)0.0203 (4)
H19A−0.02070.81090.76550.030*
H19B−0.09920.84530.67590.030*
H19C0.09010.87990.71360.030*
C200.1620 (3)0.93901 (11)0.32755 (12)0.0232 (4)
H20A0.14520.99830.30940.035*
H20B0.07630.90250.29580.035*
H20C0.28550.92090.31640.035*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ni0.01826 (18)0.00876 (17)0.01067 (17)0.00064 (10)0.00377 (11)−0.00065 (9)
O10.0266 (6)0.0109 (5)0.0127 (5)0.0024 (5)0.0038 (4)−0.0009 (4)
O20.0253 (6)0.0111 (5)0.0144 (6)0.0006 (5)0.0071 (4)−0.0013 (4)
O30.0311 (7)0.0181 (6)0.0139 (6)0.0004 (5)0.0046 (5)−0.0034 (5)
O40.0253 (6)0.0112 (5)0.0185 (6)0.0045 (5)0.0019 (5)−0.0026 (4)
O50.0298 (7)0.0148 (6)0.0135 (6)0.0034 (5)0.0054 (5)−0.0033 (4)
O60.0381 (8)0.0110 (6)0.0205 (6)0.0021 (5)0.0089 (5)0.0003 (5)
N10.0170 (7)0.0130 (6)0.0130 (6)0.0002 (5)0.0033 (5)0.0006 (5)
N20.0174 (7)0.0133 (7)0.0129 (6)0.0001 (5)0.0024 (5)0.0007 (5)
C10.0143 (7)0.0117 (7)0.0167 (8)−0.0022 (6)0.0027 (6)−0.0022 (6)
C20.0188 (8)0.0128 (8)0.0158 (8)−0.0016 (6)0.0029 (6)−0.0002 (6)
C30.0162 (8)0.0180 (8)0.0149 (8)−0.0035 (6)0.0045 (6)−0.0033 (6)
C40.0178 (8)0.0137 (8)0.0200 (8)−0.0006 (6)0.0042 (6)−0.0061 (6)
C50.0138 (7)0.0118 (7)0.0195 (8)−0.0010 (6)0.0020 (6)−0.0022 (6)
C60.0156 (7)0.0127 (8)0.0175 (8)−0.0012 (6)0.0023 (6)−0.0025 (6)
C70.0154 (8)0.0103 (7)0.0178 (8)0.0005 (6)0.0012 (6)−0.0004 (6)
C80.0229 (8)0.0131 (8)0.0134 (8)0.0023 (6)0.0046 (6)0.0025 (6)
C90.0229 (9)0.0161 (8)0.0122 (7)0.0024 (6)0.0023 (6)0.0011 (6)
C100.0176 (8)0.0164 (8)0.0128 (7)−0.0002 (6)0.0031 (6)−0.0025 (6)
C110.0173 (8)0.0127 (8)0.0166 (8)−0.0009 (6)0.0022 (6)−0.0030 (6)
C120.0192 (8)0.0159 (8)0.0145 (7)−0.0010 (6)0.0028 (6)−0.0039 (6)
C130.0244 (9)0.0127 (8)0.0196 (8)0.0001 (6)0.0044 (6)−0.0051 (6)
C140.0202 (8)0.0109 (7)0.0204 (8)−0.0006 (6)0.0027 (6)0.0006 (6)
C150.0213 (8)0.0131 (8)0.0154 (7)−0.0019 (6)0.0050 (6)−0.0012 (6)
C160.0148 (7)0.0118 (7)0.0169 (8)−0.0026 (6)0.0037 (6)−0.0023 (6)
C170.0445 (12)0.0206 (9)0.0144 (8)−0.0075 (8)0.0067 (7)0.0003 (7)
C180.0266 (9)0.0127 (8)0.0249 (9)0.0053 (7)0.0051 (7)−0.0042 (6)
C190.0239 (9)0.0187 (8)0.0186 (8)0.0024 (7)0.0061 (6)−0.0051 (6)
C200.0318 (10)0.0153 (8)0.0231 (9)0.0041 (7)0.0105 (7)0.0053 (7)
Geometric parameters (Å, °) top
Ni—N11.8448 (14)C8—C91.511 (2)
Ni—N21.8478 (14)C8—H8A0.9900
Ni—O21.8520 (12)C8—H8B0.9900
Ni—O11.8536 (12)C9—H9A0.9900
O1—C11.310 (2)C9—H9B0.9900
O2—C161.310 (2)C10—C111.418 (2)
O3—C31.356 (2)C10—H10A0.9500
O3—C171.431 (2)C11—C161.423 (2)
O4—C51.361 (2)C11—C121.431 (2)
O4—C181.4316 (19)C12—C131.368 (2)
O5—C121.369 (2)C13—C141.415 (2)
O5—C191.4311 (19)C13—H13A0.9500
O6—C141.368 (2)C14—C151.373 (2)
O6—C201.428 (2)C15—C161.413 (2)
N1—C71.295 (2)C15—H15A0.9500
N1—C81.4705 (19)C17—H17A0.9800
N2—C101.299 (2)C17—H17B0.9800
N2—C91.472 (2)C17—H17C0.9800
C1—C21.418 (2)C18—H18A0.9800
C1—C61.422 (2)C18—H18B0.9800
C2—C31.381 (2)C18—H18C0.9800
C2—H2A0.9500C19—H19A0.9800
C3—C41.406 (2)C19—H19B0.9800
C4—C51.373 (2)C19—H19C0.9800
C4—H4A0.9500C20—H20A0.9800
C5—C61.426 (2)C20—H20B0.9800
C6—C71.426 (2)C20—H20C0.9800
C7—H7A0.9500
N1—Ni—N285.95 (6)N2—C9—H9B110.5
N1—Ni—O2177.34 (6)C8—C9—H9B110.5
N2—Ni—O294.11 (6)H9A—C9—H9B108.7
N1—Ni—O193.64 (6)N2—C10—C11124.68 (15)
N2—Ni—O1176.89 (6)N2—C10—H10A117.7
O2—Ni—O186.44 (5)C11—C10—H10A117.7
C1—O1—Ni126.87 (11)C10—C11—C16121.80 (15)
C16—O2—Ni127.42 (10)C10—C11—C12119.46 (15)
C3—O3—C17117.05 (13)C16—C11—C12118.73 (15)
C5—O4—C18116.65 (13)C13—C12—O5123.95 (15)
C12—O5—C19117.32 (13)C13—C12—C11121.68 (15)
C14—O6—C20116.69 (13)O5—C12—C11114.37 (14)
C7—N1—C8119.28 (14)C12—C13—C14118.19 (15)
C7—N1—Ni127.27 (12)C12—C13—H13A120.9
C8—N1—Ni113.45 (10)C14—C13—H13A120.9
C10—N2—C9118.73 (13)O6—C14—C15123.75 (15)
C10—N2—Ni127.03 (12)O6—C14—C13113.77 (15)
C9—N2—Ni114.24 (11)C15—C14—C13122.48 (15)
O1—C1—C2117.36 (14)C14—C15—C16119.78 (15)
O1—C1—C6123.69 (15)C14—C15—H15A120.1
C2—C1—C6118.94 (14)C16—C15—H15A120.1
C3—C2—C1119.91 (15)O2—C16—C15117.64 (14)
C3—C2—H2A120.0O2—C16—C11123.25 (15)
C1—C2—H2A120.0C15—C16—C11119.11 (15)
O3—C3—C2124.24 (16)O3—C17—H17A109.5
O3—C3—C4113.82 (15)O3—C17—H17B109.5
C2—C3—C4121.94 (15)H17A—C17—H17B109.5
C5—C4—C3118.66 (15)O3—C17—H17C109.5
C5—C4—H4A120.7H17A—C17—H17C109.5
C3—C4—H4A120.7H17B—C17—H17C109.5
O4—C5—C4123.50 (15)O4—C18—H18A109.5
O4—C5—C6114.92 (14)O4—C18—H18B109.5
C4—C5—C6121.58 (15)H18A—C18—H18B109.5
C1—C6—C7121.24 (15)O4—C18—H18C109.5
C1—C6—C5118.77 (15)H18A—C18—H18C109.5
C7—C6—C5119.70 (15)H18B—C18—H18C109.5
N1—C7—C6123.96 (15)O5—C19—H19A109.5
N1—C7—H7A118.0O5—C19—H19B109.5
C6—C7—H7A118.0H19A—C19—H19B109.5
N1—C8—C9106.45 (13)O5—C19—H19C109.5
N1—C8—H8A110.4H19A—C19—H19C109.5
C9—C8—H8A110.4H19B—C19—H19C109.5
N1—C8—H8B110.4O6—C20—H20A109.5
C9—C8—H8B110.4O6—C20—H20B109.5
H8A—C8—H8B108.6H20A—C20—H20B109.5
N2—C9—C8106.22 (13)O6—C20—H20C109.5
N2—C9—H9A110.5H20A—C20—H20C109.5
C8—C9—H9A110.5H20B—C20—H20C109.5
N1—Ni—O1—C1−16.22 (14)O4—C5—C6—C7−8.9 (2)
N2—Ni—O1—C1−98.5 (11)C4—C5—C6—C7171.01 (15)
O2—Ni—O1—C1161.12 (14)C8—N1—C7—C6171.34 (15)
N1—Ni—O2—C16−105.1 (12)Ni—N1—C7—C6−8.6 (2)
N2—Ni—O2—C16−13.82 (14)C1—C6—C7—N1−8.2 (3)
O1—Ni—O2—C16163.11 (14)C5—C6—C7—N1177.99 (16)
N2—Ni—N1—C7−165.37 (15)C7—N1—C8—C9146.29 (15)
O2—Ni—N1—C7−73.9 (12)Ni—N1—C8—C9−33.74 (16)
O1—Ni—N1—C717.72 (15)C10—N2—C9—C8151.31 (15)
N2—Ni—N1—C814.66 (12)Ni—N2—C9—C8−29.43 (16)
O2—Ni—N1—C8106.1 (12)N1—C8—C9—N238.49 (17)
O1—Ni—N1—C8−162.25 (11)C9—N2—C10—C11175.76 (15)
N1—Ni—N2—C10−171.54 (15)Ni—N2—C10—C11−3.4 (3)
O2—Ni—N2—C1011.12 (15)N2—C10—C11—C16−6.4 (3)
O1—Ni—N2—C10−89.0 (11)N2—C10—C11—C12175.06 (16)
N1—Ni—N2—C99.28 (12)C19—O5—C12—C1314.1 (2)
O2—Ni—N2—C9−168.06 (11)C19—O5—C12—C11−165.63 (15)
O1—Ni—N2—C991.8 (11)C10—C11—C12—C13177.11 (16)
Ni—O1—C1—C2−175.30 (11)C16—C11—C12—C13−1.5 (3)
Ni—O1—C1—C65.7 (2)C10—C11—C12—O5−3.2 (2)
O1—C1—C2—C3178.92 (15)C16—C11—C12—O5178.18 (14)
C6—C1—C2—C3−2.0 (2)O5—C12—C13—C14−179.25 (16)
C17—O3—C3—C25.6 (2)C11—C12—C13—C140.4 (3)
C17—O3—C3—C4−173.47 (16)C20—O6—C14—C15−0.1 (3)
C1—C2—C3—O3178.78 (15)C20—O6—C14—C13−179.51 (15)
C1—C2—C3—C4−2.2 (3)C12—C13—C14—O6−179.43 (16)
O3—C3—C4—C5−177.02 (15)C12—C13—C14—C151.1 (3)
C2—C3—C4—C53.9 (2)O6—C14—C15—C16179.13 (16)
C18—O4—C5—C4−1.1 (2)C13—C14—C15—C16−1.5 (3)
C18—O4—C5—C6178.73 (14)Ni—O2—C16—C15−170.27 (11)
C3—C4—C5—O4178.62 (15)Ni—O2—C16—C118.7 (2)
C3—C4—C5—C6−1.2 (2)C14—C15—C16—O2179.34 (15)
O1—C1—C6—C79.7 (3)C14—C15—C16—C110.3 (2)
C2—C1—C6—C7−169.32 (15)C10—C11—C16—O23.6 (3)
O1—C1—C6—C5−176.52 (15)C12—C11—C16—O2−177.85 (15)
C2—C1—C6—C54.5 (2)C10—C11—C16—C15−177.45 (15)
O4—C5—C6—C1177.22 (14)C12—C11—C16—C151.1 (2)
C4—C5—C6—C1−2.9 (2)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C8—H8B···O2i0.992.613.587 (2)169
C17—H17A···O4ii0.982.603.484 (2)150
Symmetry codes: (i) −x, −y+1, −z+1; (ii) x, −y+1/2, z−1/2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C8—H8B···O2i0.992.613.587 (2)169
C17—H17A···O4ii0.982.603.484 (2)150
Symmetry codes: (i) −x, −y+1, −z+1; (ii) x, −y+1/2, z−1/2.
Acknowledgements top

RJB wishes to acknowledge the NSF-MRI program (grant CHE-0619278) for funds to purchase the diffractometer.

references
References top

Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1–19.

Bal, T. & Ülküseven, B. (2004). Transition Met. Chem. 29, 880–884.

Blake, A. B., Chipperfield, J. R., Hussain, W., Paschke, R. & Sinn, E. (1995). Inorg. Chem. 34, 1125–1129.

Oxford Diffraction (2007). CrysAlis PRO. Oxford Diffraction Ltd, Abingdon, England.

Santos, I. C., Vilas-Boas, M., Piedade, M. F. M., Freire, C., Duarte, M. T. & De Castro, B. (2000). Polyhedron, 19, 655–664.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Silva, A. R., Martins, M., Freitas, M. M. A., Valente, A., Castro de, B. & Figueirodo, J. L. (2002). Micropor. Mesopor. Mater. 55, 275–284.

Soto-Garrodo, G. & Salas-Reyes, V. (2000). Transition Met. Chem. 25, 192–195.

Yoon, H. & Burrows, C. J. (1988). J. Am. Chem. Soc. 110, 4087–4089.