supplementary materials


zl2518 scheme

Acta Cryst. (2013). E69, m24-m25    [ doi:10.1107/S1600536812049380 ]

Aqua{2-(pyridin-2-yl)-N-[(pyridin-2-yl)methylidene]ethanamine-[kappa]3N,N',N''}(sulfato-[kappa]2O,O')copper(II) tetrahydrate

D. Tinguiano, M. M. Sow, F. B. Tamboura, A. H. Barry and M. Gaye

Abstract top

The title complex, [Cu(SO4)(C13H13N3)(H2O)]·4H2O, was obtained by mixing copper sulfate pentahydrate and 2-(pyridin-2-yl)-N-(pyridin-2-ylmethylidene)ethanamine in ethanol under reflux conditions. The CuII ion shows a Jahn-Teller-distorted octahedral geometry, with equatorial positions occupied by three N atoms from the tridentate ligand (average Cu-N = 2.004 Å) and one O atom from a bidentate sulfate anion [Cu-O = 1.963 (2) Å]. The axial positions are occupied by one O atom from a coordinating water molecule [Cu-O = 2.230 (3) Å] and one weakly bonded O atom [Cu-O = 2.750 (2) Å] from the bidentate sulfate ion. The complex molecules are connected through O-H...O hydrogen bonds between the coordinating water molecules and sulfate ions from neighboring complexes, forming a double chain parallel to the c axis. The chains are stabilized through additional hydrogen bonds by one of the non-coordinating water molecules bridging between neighboring strands of the double chains. The remaining three water molecules fill the interstitial space between the double chains and are involved in an intricate hydrogen-bonding network that consolidates the structure.

Comment top

The title complex, [Cu(SO4)(H2O)(C13H13N3)](H2O)4, was obtained by mixing copper sulfate pentahydrate and 2-(pyridin-2-yl)-N-(pyridin-2-ylmethylidene)ethanamine in ethanol under reflux conditions. It consists of a mononuclear Cu(II) complex and solvate water molecules with one neutral complex molecule and four not coordinated water molecules in the asymmetric unit (Fig. 1). The Cu(II) ion displays a six coordinated-geometry where the Cu atom is coordinated by three nitrogen atoms from the ligand molecule, two O atoms from the SO42- sulfate moiety and one O atom from a coordinated water molecule. The bond distances between the N atoms and the metal ion vary between 1.965 (3) Å [Cu1—N3] and 2.030 (3) Å [Cu1—N1]. These values are comparable to the bond lengths in a similar copper complex [1.971 (4)–2.021 (3) Å] (de Bettencourt-Dias et al., 2010). The Cu—O bond distance for Cu1—O1 of the sulfate ion is 1.963 (2) Å, which is in the typical range (Liu et al., 2010). The remaining positions are occupied by one O atom from a coordinated water molecule (Cu—O = 2.230 (3) Å) and one weakly coordinated O (Cu—O = 2.750 (2) Å) atom from the bidentate sulfate ion. The angle between the central metal ion and the O atoms [O1—Cu1—O5W] is equal to 98.24 (10) °. The angles between the CuII ion and the coordinating N atoms vary between 80.77 (13) ° [N3—Cu1—N1] and 174.29 (12) ° [N2—Cu1—N1]. The Cu(II) center of the molecule complex thus adopts a distorted octahedral geometry. Atoms [N1, N2, N3, O1] are arranged in the equatorial plane with some deviations from the ideal geometry. The axial positions are occupied by the oxygen atom of the coordinated water molecule and one O atom from the bidentate sulfate. The axial bond lengths between the CuII ion and the O atoms are considerably longer than the equatorial bond distances between the CuII ion and the O atom of the sulfate ligand as a consequence of the Jahn–Teller effect (Jahn & Teller, 1937).

The sulfate anion has a slightly distorted tetrahedral geometry due to the fact that two of the oxygen atoms of the sulfate group are coordinated to the metal center, with one of the Cu—O distances being considerably longer than the other one (1.963 (2) and 2.750 (2) Å). The S—O bond lengths (S—O4 = 1.450 (3); S—O3 = 1.459 (3); S—O2 = 1.462 (3) and S—O1 = 1.517 (2) Å) indicate a S—O single bond for the tightly copper bonded O atom and S—O bonds between single and double bond character for the other three. The O—S—O angles, which range from 107.01 (15) to 111.23 (16) °, are close to the ideal tetrahedral angle value of 109.5 °.

Neighboring [Cu(SO4)(H2O)(C13H13N3)] units are connected with each other through hydrogen bonds creating double chains that stretch parallel to the c axis direction (Fig 2, Fig. 3). The coordinated water molecules are connected with complexes through OW—H···O—SO3 hydrogen bonds between O5W and O2 and O1 of neighboring complexes' sulfate ions. The double chains thus created are in addition connected with each other through O—H···O hydrogen bonds mediated by the uncoordinated water molecule of O7W which acts as bridge between two sulfate groups of two molecules belonging to parallel strands of the double chains (SO3—O···H—OW—H···O—SO3) (Table 1). The interstitial space between the double chains is filled by the three remaining lattice water molecules which are involved in an intricate hydrogen bonding network that consolidates the crystal packing.

Related literature top

For related structures: see: de Bettencourt-Dias et al. (2010); Liu et al. (2010). For the Jahn–Teller effect, see: Jahn & Teller (1937).

Experimental top

2-(Pyridin-2-yl)-N-(pyridin-2-ylmethylidene)ethanamine (0.2111 g, 1 mmol) was dissolved in 10 ml of ethanol. To the resulting solution, Cu(SO4).5H2O (0.2497 g, 1 mmol) was added. The mixture was stirred at room temperature for 2 h. The green solution was filtered off and left for slow evaporation. Crystals that separated from the green solution, were filtered off and recrystallized from dimethylformamide. On standing for two weeks, crystals suitable for X-ray diffraction analysis were obtained. Yield: 74.5%. Anal. Calc. for [C13H23N3O9SCu] (%): C, 33.87; H, 5.03; N, 9.12; S, 6.96. Found: C, 33.84; H, 5.01; N, 9.09; S, 6.98. Decomposition point: 305 °C. Selected IR data (cm-1, KBr pellet): 3445 s (νOH), 1646 s (νCN), 1598 m, 1109 m (νasSO4), 774 m.

Refinement top

H atoms of the water molecule were located in the Fourier difference maps and refined with O—H distance restraints of 0.82 (2) Å. Additional H···O distance restraints were used for H atoms of two water molecules (O8W and O9W). H atoms of =CH and CH2 groups were placed geometrically and refined using a riding model with C—H distantces between 0.93 and 0.97 Å with Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. An ORTEP view of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are plotted at the 50% probability level.
[Figure 2] Fig. 2. Molecular representation of the compound showing hydrogen bonds in the bc plane.
[Figure 3] Fig. 3. View of the structure along the c axis.
Aqua{2-(pyridin-2-yl)-N-[(pyridin-2-yl)methylidene]ethanamine- κ3N,N',N''}(sulfato-κ2O,O')copper(II) tetrahydrate top
Crystal data top
[Cu(SO4)(C13H13N3)(H2O)]·4H2OF(000) = 956
Mr = 460.94Dx = 1.591 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 25 reflections
a = 10.7315 (17) Åθ = 11–15°
b = 23.605 (4) ŵ = 1.29 mm1
c = 7.6478 (12) ÅT = 293 K
β = 96.523 (3)°Prismatic, blue
V = 1924.8 (5) Å30.10 × 0.07 × 0.05 mm
Z = 4
Data collection top
Enraf–Nonius CAD-4
diffractometer
Rint = 0.039
Radiation source: fine-focus sealed tubeθmax = 25.1°, θmin = 1.7°
Graphite monochromatorh = 1212
π scansk = 2828
14560 measured reflectionsl = 89
3403 independent reflections2 standard reflections every 60 min
2620 reflections with I > 2σ(I) intensity decay: none
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)] = 0.037Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.103H atoms treated by a mixture of independent and constrained refinement
S = 1.04 w = 1/[σ2(Fo2) + (0.0448P)2 + 2.5709P]
where P = (Fo2 + 2Fc2)/3
3403 reflections(Δ/σ)max = 0.001
274 parametersΔρmax = 0.57 e Å3
17 restraintsΔρmin = 0.39 e Å3
Crystal data top
[Cu(SO4)(C13H13N3)(H2O)]·4H2OV = 1924.8 (5) Å3
Mr = 460.94Z = 4
Monoclinic, P21/cMo Kα radiation
a = 10.7315 (17) ŵ = 1.29 mm1
b = 23.605 (4) ÅT = 293 K
c = 7.6478 (12) Å0.10 × 0.07 × 0.05 mm
β = 96.523 (3)°
Data collection top
Enraf–Nonius CAD-4
diffractometer
Rint = 0.039
14560 measured reflectionsθmax = 25.1°
3403 independent reflections2 standard reflections every 60 min
2620 reflections with I > 2σ(I) intensity decay: none
Refinement top
R[F2 > 2σ(F2)] = 0.037H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.103Δρmax = 0.57 e Å3
S = 1.04Δρmin = 0.39 e Å3
3403 reflectionsAbsolute structure: ?
274 parametersFlack parameter: ?
17 restraintsRogers parameter: ?
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
xyzUiso*/Ueq
Cu10.34621 (4)0.409141 (17)0.46361 (5)0.03121 (15)
S10.34297 (8)0.41815 (3)0.84451 (11)0.0315 (2)
N10.2175 (3)0.47177 (13)0.4132 (4)0.0385 (7)
N20.4622 (3)0.34185 (12)0.4987 (4)0.0362 (7)
N30.2371 (3)0.37299 (13)0.2717 (4)0.0405 (7)
O10.4070 (2)0.44192 (9)0.6934 (3)0.0348 (6)
O20.4420 (2)0.39896 (11)0.9786 (3)0.0437 (6)
O30.2646 (3)0.37097 (11)0.7753 (4)0.0485 (7)
O40.2680 (3)0.46243 (11)0.9121 (4)0.0506 (7)
O5W0.4827 (3)0.45044 (11)0.3049 (3)0.0424 (6)
H5WA0.473 (4)0.4385 (19)0.207 (3)0.064*
H5WB0.498 (4)0.4833 (9)0.301 (6)0.064*
O6W0.0350 (4)0.3126 (2)0.7184 (8)0.1132 (17)
H6WA0.038 (5)0.308 (4)0.609 (3)0.170*
H6WB0.103 (4)0.328 (3)0.719 (10)0.170*
O7W0.3003 (3)0.57344 (17)1.0390 (7)0.0916 (13)
H7WA0.372 (3)0.583 (2)1.034 (10)0.137*
H7WB0.287 (6)0.5420 (15)0.996 (9)0.137*
O8W0.0444 (6)0.2896 (3)0.3565 (9)0.158 (2)
H8WA0.086 (7)0.307 (5)0.275 (8)0.237*
H8WB0.026 (12)0.2552 (16)0.348 (9)0.237*
O9W0.1188 (4)0.3475 (2)0.0284 (9)0.1241 (18)
H9WA0.185 (5)0.367 (3)0.025 (11)0.186*
H9WB0.086 (7)0.332 (3)0.054 (9)0.186*
C10.2128 (4)0.52248 (16)0.4895 (6)0.0470 (10)
H10.27460.53240.57950.056*
C20.1173 (4)0.56075 (18)0.4370 (6)0.0567 (12)
H20.11720.59630.48930.068*
C30.0239 (4)0.5461 (2)0.3089 (6)0.0580 (12)
H30.04150.57110.27540.070*
C40.0278 (4)0.4941 (2)0.2304 (6)0.0541 (11)
H40.03510.48310.14330.065*
C50.1269 (4)0.45822 (17)0.2829 (5)0.0430 (9)
C60.1431 (4)0.40272 (18)0.2065 (5)0.0482 (10)
H60.08740.38930.11380.058*
C70.2575 (4)0.31678 (16)0.2077 (5)0.0503 (10)
H7A0.32070.31790.12660.060*
H7B0.18040.30240.14490.060*
C80.3000 (4)0.27820 (16)0.3600 (5)0.0500 (10)
H8A0.24290.28240.44870.060*
H8B0.29420.23930.31890.060*
C90.4305 (4)0.28867 (14)0.4440 (5)0.0392 (9)
C100.5785 (4)0.35136 (17)0.5752 (5)0.0471 (10)
H100.59990.38790.61240.056*
C110.6683 (4)0.3095 (2)0.6015 (7)0.0625 (12)
H110.74860.31770.65440.075*
C120.6360 (5)0.2554 (2)0.5476 (7)0.0686 (14)
H120.69420.22620.56450.082*
C130.5164 (5)0.24484 (17)0.4684 (6)0.0547 (11)
H130.49360.20840.43140.066*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cu10.0333 (3)0.0289 (2)0.0306 (2)0.00165 (18)0.00006 (17)0.00066 (17)
S10.0346 (5)0.0302 (4)0.0292 (4)0.0022 (4)0.0015 (4)0.0004 (3)
N10.0333 (17)0.0444 (18)0.0375 (17)0.0019 (14)0.0036 (14)0.0055 (14)
N20.0410 (18)0.0299 (16)0.0383 (17)0.0020 (13)0.0066 (14)0.0004 (13)
N30.0452 (19)0.0429 (18)0.0338 (17)0.0106 (15)0.0058 (15)0.0040 (14)
O10.0449 (15)0.0314 (13)0.0277 (13)0.0065 (11)0.0029 (11)0.0003 (10)
O20.0460 (16)0.0490 (16)0.0342 (14)0.0025 (12)0.0033 (12)0.0082 (11)
O30.0494 (16)0.0459 (16)0.0499 (16)0.0195 (13)0.0044 (13)0.0039 (12)
O40.0543 (17)0.0475 (16)0.0516 (17)0.0106 (13)0.0135 (14)0.0051 (13)
O5W0.0552 (17)0.0403 (15)0.0321 (14)0.0134 (13)0.0071 (13)0.0004 (12)
O6W0.073 (3)0.067 (3)0.190 (5)0.012 (2)0.029 (3)0.005 (3)
O7W0.053 (2)0.075 (3)0.150 (4)0.0019 (18)0.021 (3)0.035 (3)
O8W0.113 (4)0.190 (7)0.169 (6)0.042 (5)0.009 (4)0.019 (5)
O9W0.068 (3)0.108 (4)0.190 (6)0.001 (3)0.012 (3)0.029 (4)
C10.045 (2)0.039 (2)0.056 (3)0.0024 (18)0.004 (2)0.0026 (18)
C20.054 (3)0.038 (2)0.079 (3)0.011 (2)0.014 (3)0.009 (2)
C30.042 (3)0.059 (3)0.073 (3)0.012 (2)0.012 (2)0.025 (2)
C40.040 (2)0.071 (3)0.050 (3)0.008 (2)0.0033 (19)0.016 (2)
C50.039 (2)0.049 (2)0.040 (2)0.0007 (18)0.0015 (17)0.0068 (18)
C60.046 (2)0.059 (3)0.037 (2)0.004 (2)0.0036 (18)0.0018 (19)
C70.062 (3)0.044 (2)0.045 (2)0.012 (2)0.009 (2)0.0068 (18)
C80.062 (3)0.036 (2)0.052 (2)0.0040 (19)0.008 (2)0.0066 (18)
C90.052 (2)0.0287 (18)0.038 (2)0.0014 (17)0.0127 (18)0.0010 (15)
C100.045 (2)0.040 (2)0.056 (3)0.0015 (18)0.006 (2)0.0012 (18)
C110.046 (3)0.061 (3)0.079 (3)0.010 (2)0.001 (2)0.002 (2)
C120.067 (3)0.054 (3)0.086 (4)0.027 (2)0.013 (3)0.008 (3)
C130.074 (3)0.032 (2)0.060 (3)0.008 (2)0.016 (2)0.0025 (19)
Geometric parameters (Å, º) top
Cu1—O11.963 (2)C1—C21.390 (5)
Cu1—N31.965 (3)C1—H10.9300
Cu1—N22.017 (3)C2—C31.364 (6)
Cu1—N12.030 (3)C2—H20.9300
Cu1—O5W2.230 (3)C3—C41.370 (6)
S1—O41.450 (3)C3—H30.9300
S1—O31.459 (3)C4—C51.383 (5)
S1—O21.462 (3)C4—H40.9300
S1—O11.517 (2)C5—C61.453 (6)
N1—C11.335 (5)C6—H60.9300
N1—C51.349 (5)C7—C81.508 (6)
N2—C101.336 (5)C7—H7A0.9700
N2—C91.354 (4)C7—H7B0.9700
N3—C61.282 (5)C8—C91.494 (6)
N3—C71.440 (5)C8—H8A0.9700
O5W—H5WA0.796 (19)C8—H8B0.9700
O5W—H5WB0.793 (19)C9—C131.384 (5)
O6W—H6WA0.844 (19)C10—C111.379 (6)
O6W—H6WB0.822 (17)C10—H100.9300
O7W—H7WA0.81 (2)C11—C121.374 (7)
O7W—H7WB0.817 (19)C11—H110.9300
O8W—H8WA0.828 (19)C12—C131.378 (7)
O8W—H8WB0.84 (2)C12—H120.9300
O9W—H9WA0.840 (19)C13—H130.9300
O9W—H9WB0.843 (18)
O1—Cu1—N3161.62 (12)C2—C3—C4119.0 (4)
O1—Cu1—N293.10 (11)C2—C3—H3120.5
N3—Cu1—N293.65 (13)C4—C3—H3120.5
O1—Cu1—N191.87 (11)C3—C4—C5118.9 (4)
N3—Cu1—N180.77 (13)C3—C4—H4120.6
N2—Cu1—N1174.28 (12)C5—C4—H4120.6
O1—Cu1—O5W98.24 (10)N1—C5—C4122.3 (4)
N3—Cu1—O5W98.95 (11)N1—C5—C6113.7 (3)
N2—Cu1—O5W89.05 (11)C4—C5—C6124.0 (4)
N1—Cu1—O5W93.05 (11)N3—C6—C5117.5 (4)
O4—S1—O3111.05 (17)N3—C6—H6121.2
O4—S1—O2111.23 (16)C5—C6—H6121.2
O3—S1—O2111.19 (16)N3—C7—C8109.8 (3)
O4—S1—O1108.81 (15)N3—C7—H7A109.7
O3—S1—O1107.35 (14)C8—C7—H7A109.7
O2—S1—O1107.01 (15)N3—C7—H7B109.7
C1—N1—C5118.4 (3)C8—C7—H7B109.7
C1—N1—Cu1129.0 (3)H7A—C7—H7B108.2
C5—N1—Cu1112.7 (2)C9—C8—C7114.8 (3)
C10—N2—C9118.7 (3)C9—C8—H8A108.6
C10—N2—Cu1117.2 (2)C7—C8—H8A108.6
C9—N2—Cu1124.0 (3)C9—C8—H8B108.6
C6—N3—C7121.0 (3)C7—C8—H8B108.6
C6—N3—Cu1115.4 (3)H8A—C8—H8B107.5
C7—N3—Cu1123.6 (3)N2—C9—C13120.8 (4)
S1—O1—Cu1113.77 (13)N2—C9—C8118.4 (3)
Cu1—O5W—H5WA110 (3)C13—C9—C8120.8 (4)
Cu1—O5W—H5WB127 (3)N2—C10—C11123.1 (4)
H5WA—O5W—H5WB109 (5)N2—C10—H10118.4
H6WA—O6W—H6WB85 (6)C11—C10—H10118.4
H7WA—O7W—H7WB112 (3)C12—C11—C10118.2 (4)
H8WA—O8W—H8WB122 (10)C12—C11—H11120.9
H9WA—O9W—H9WB130 (9)C10—C11—H11120.9
N1—C1—C2121.3 (4)C11—C12—C13119.4 (4)
N1—C1—H1119.3C11—C12—H12120.3
C2—C1—H1119.3C13—C12—H12120.3
C3—C2—C1120.0 (4)C12—C13—C9119.7 (4)
C3—C2—H2120.0C12—C13—H13120.1
C1—C2—H2120.0C9—C13—H13120.1
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O5W—H5WA···O2i0.80 (2)1.97 (2)2.765 (4)172 (5)
O5W—H5WB···O1ii0.79 (2)2.04 (2)2.803 (3)162 (5)
O6W—H6WA···O8W0.84 (2)2.08 (2)2.854 (9)152 (5)
O6W—H6WB···O30.82 (2)2.01 (2)2.814 (5)167 (8)
O7W—H7WA···O2iii0.81 (2)2.05 (2)2.859 (5)175 (6)
O7W—H7WB···O40.82 (2)1.99 (2)2.802 (5)174 (7)
O8W—H8WA···O9W0.83 (2)2.11 (2)2.890 (10)156 (6)
O9W—H9WA···O7Wiv0.84 (2)1.91 (2)2.705 (6)158 (6)
O9W—H9WB···O6Wi0.84 (2)2.33 (2)3.148 (8)164 (7)
C1—H1···O10.932.663.107 (5)111
C6—H6···O9W0.932.443.254 (6)146
C7—H7A···O2i0.972.643.398 (5)135
C10—H10···O10.932.573.025 (5)111
Symmetry codes: (i) x, y, z1; (ii) x+1, y+1, z+1; (iii) x+1, y+1, z+2; (iv) x, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O5W—H5WA···O2i0.796 (19)1.97 (2)2.765 (4)172 (5)
O5W—H5WB···O1ii0.793 (19)2.04 (2)2.803 (3)162 (5)
O6W—H6WA···O8W0.844 (19)2.082 (19)2.854 (9)152 (5)
O6W—H6WB···O30.822 (17)2.007 (17)2.814 (5)167 (8)
O7W—H7WA···O2iii0.81 (2)2.05 (2)2.859 (5)175 (6)
O7W—H7WB···O40.817 (19)1.99 (2)2.802 (5)174 (7)
O8W—H8WA···O9W0.828 (19)2.11 (2)2.890 (10)156 (6)
O9W—H9WA···O7Wiv0.840 (19)1.906 (19)2.705 (6)158 (6)
O9W—H9WB···O6Wi0.843 (18)2.328 (18)3.148 (8)164 (7)
C1—H1···O10.932.663.107 (5)110.5
C6—H6···O9W0.932.443.254 (6)145.7
C7—H7A···O2i0.972.643.398 (5)135.0
C10—H10···O10.932.573.025 (5)110.9
Symmetry codes: (i) x, y, z1; (ii) x+1, y+1, z+1; (iii) x+1, y+1, z+2; (iv) x, y+1, z+1.
references
References top

Bettencourt-Dias, A. de, Scott, V. J. & Hugdal, S. (2010). Inorg. Chim. Acta, 363, 4088–4095.

Enraf–Nonius (1994). CAD-4 EXPRESS. Enraf–Nonius, Delft, The Netherlands.

Fair, C. K. (1990). MolEN. Enraf–Nonius, Delft, The Netherlands.

Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854.

Jahn, H. A. & Teller, E. (1937). Proc. R. Soc. London Ser. A, 161, 220–235.

Liu, K., Zhu, X., Wang, J., Li, B. & Zhang, Y. (2010). Inorg. Chem. Commun. 13, 976–980.

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