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Acta Cryst. (2007). E63, m2872-m2873    [ doi:10.1107/S1600536807053998 ]

Diaquabis[5-(pyrimidin-2-yl-[kappa]N)tetrazolato-[kappa]N1]nickel(II)

Y.-E. Qiu

Abstract top

In the title complex, [Ni(C5H3N6)2(H2O)2], the NiII atom is located in a general position and is coordinated by four N atoms from two 5-(pyrimidin-2-yl)tetrazolate ligands and O atoms of two water molecules in a distorted octahedral geometry. The bond distances and angles around the metal center lie in the ranges 2.051 (5)-2.097 (5) Å and 78.88 (19)-101.22 (19)°, respectively. The title complex is isostructural with its MnII and CuII analogues; it is, however, structurally different from an NiII complex obtained by direct reaction of 2-(1H-tetrazol-5-yl)pyrimidine with an NiII salt under hydrothermal conditions. In the crystal structure, molecules are linked together by O-H...N hydrogen bonds, forming a two-dimensional network parallel to the (001) plane.

Comment top

The syntheses and crystal structures of NaII, MnII, FeII, CoII, NiII, CuII and ZnII complexes with 5-(pyrimidin-2-yl)tetrazolate group have been reported (Jin et al., 2007; Liu & Fan, 2007a,b; Rodríguez et al., 2005, 2006, 2007; Zhang et al., 2007). Such complexes were obtained by different methods and the ligand performed several coordination modes. Except the MnII and CuII complexes, which are mononuclear being similar to the title complex, other complexes have an extended structure. It is interesting to note that the two NiII complexes of this ligand obtained by different synthesis methods, the direct reaction of 2-(1H-tetrazol-5-yl)pyrimidine and the in situ reaction (this report) from pyrimidine-2-carbonitrile in the presence of NaN3 with nickel(II) salt under the hydrothermal condition, have different structures, indicating the influence of synthesis method on the formation of complexes and the coordination diversity of the ligand.

The title complex has a mononuclear structure (Fig. 1). The NiII atom, located in a general position, is coordinated by two ligands using pyrimidine and tetrazole N atoms in the 1-position and two water molecules in the trans positions. The coordination bond distances and angles are normal (Table 1). In the crystal structure, the complex molecules are linked via Ow—H···N hydrogen bonds, forming a two-dimensional network parallel to the (0 0 1) plane (Fig. 2). The hydrogen bond parameters are listed in Table 2.

Related literature top

For related literature, see: Jin et al. (2007); Liu & Fan (2007a,b); Rodríguez et al. (2005, 2006, 2007); Zhang et al. (2007).

Experimental top

A mixture of NiCl2·6H2O (24 mg, 0.1 mmol), NaN3 (26 mg, 0.4 mmol) and pyrimidine-2-carbonitrile (21 mg, 0.2 mmol) in water (8 ml) was placed in a Teflon-lined stainless-steel Parr bomb that was heated at 393 K for 48 h. Pale purple crystals of the title compound were collected after the bomb was subsequently allowed to cool to room temperature (yield 10%). Caution: Azide and tetrazole derivatives are potentially explosive. Although we have met no problems in this work, only a small amount of them should be prepared and handled with great caution.

Refinement top

H atoms of water molecules were located in a difference map and refined with bond restraints O—H = 0.85 (2) Å, and with Uiso(H) = 1.5Ueq(O). The remaining H atoms were included in calculated positions and treated in the subsequent refinement as riding atoms, with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT (Bruker, 1998); 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
[Figure 1] Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. Part of a hydrogen-bonded (dashed lines) two-dimensional network in the title compound.
Diaquabis[5-(pyrimidin-2-yl-κN)tetrazolato-κN1]nickel(II) top
Crystal data top
[Ni(C5H3N6)2(H2O)2]F000 = 792
Mr = 389.01Dx = 1.819 Mg m−3
Monoclinic, P21/cMo Kα radiation
λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3850 reflections
a = 7.1271 (14) Åθ = 2.1–27.9º
b = 12.707 (3) ŵ = 1.41 mm−1
c = 16.401 (4) ÅT = 113 (2) K
β = 106.95 (3)ºBlock, pink
V = 1420.8 (6) Å30.20 × 0.20 × 0.18 mm
Z = 4
Data collection top
Bruker Smart CCD area-detector
diffractometer		2556 independent reflections
Radiation source: fine-focus sealed tube2113 reflections with I > 2σ(I)
Monochromator: graphiteRint = 0.086
T = 113(2) Kθmax = 25.3º
φ and ω scansθmin = 2.1º
Absorption correction: multi-scan
(SADABS; Bruker, 1998)		h = −8→8
Tmin = 0.766, Tmax = 1.000k = −15→15
8530 measured reflectionsl = −19→13
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.079H atoms treated by a mixture of
independent and constrained refinement
wR(F2) = 0.189  w = 1/[σ2(Fo2) + (0.086P)2 + 8.6013P]
where P = (Fo2 + 2Fc2)/3
S = 1.00(Δ/σ)max = 0.001
2556 reflectionsΔρmax = 0.55 e Å−3
238 parametersΔρmin = −0.66 e Å−3
30 restraintsExtinction correction: none
Primary atom site location: structure-invariant direct methods
Crystal data top
[Ni(C5H3N6)2(H2O)2]V = 1420.8 (6) Å3
Mr = 389.01Z = 4
Monoclinic, P21/cMo Kα
a = 7.1271 (14) ŵ = 1.41 mm−1
b = 12.707 (3) ÅT = 113 (2) K
c = 16.401 (4) Å0.20 × 0.20 × 0.18 mm
β = 106.95 (3)º
Data collection top
Bruker Smart CCD area-detector
diffractometer		2556 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 1998)		2113 reflections with I > 2σ(I)
Tmin = 0.766, Tmax = 1.000Rint = 0.086
8530 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.07930 restraints
wR(F2) = 0.189H atoms treated by a mixture of
independent and constrained refinement
S = 1.00Δρmax = 0.55 e Å−3
2556 reflectionsΔρmin = −0.66 e Å−3
238 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
xyzUiso*/Ueq
Ni10.25242 (11)0.47686 (6)0.24666 (5)0.0118 (3)
N10.2788 (7)0.3174 (4)0.2683 (3)0.0132 (11)
N20.3804 (7)0.2494 (4)0.3253 (3)0.0152 (11)
N30.3235 (7)0.1528 (4)0.2983 (3)0.0143 (11)
N40.1851 (7)0.1586 (4)0.2219 (3)0.0157 (11)
N50.0297 (7)0.4194 (4)0.1424 (3)0.0126 (11)
N6−0.0996 (7)0.2598 (4)0.0717 (3)0.0194 (12)
N70.2223 (7)0.6361 (4)0.2268 (3)0.0155 (12)
N80.1181 (7)0.7071 (4)0.1701 (3)0.0150 (11)
N90.1716 (8)0.8014 (4)0.2017 (3)0.0162 (11)
N100.3094 (7)0.7949 (4)0.2779 (3)0.0139 (11)
N110.4738 (7)0.5319 (4)0.3520 (3)0.0141 (11)
N120.5935 (8)0.6925 (4)0.4264 (3)0.0176 (12)
C10.0196 (8)0.3148 (5)0.1342 (4)0.0124 (13)
C20.1624 (9)0.2607 (5)0.2061 (4)0.0135 (13)
C3−0.1014 (10)0.4764 (5)0.0838 (4)0.0201 (14)
H3A−0.10060.55100.08800.024*
C4−0.2378 (9)0.4268 (6)0.0170 (4)0.0215 (15)
H4A−0.33380.4658−0.02430.026*
C5−0.2285 (9)0.3175 (5)0.0131 (4)0.0180 (14)
H5A−0.31770.2823−0.03340.022*
C60.3364 (9)0.6922 (4)0.2920 (4)0.0127 (13)
C70.4767 (9)0.6372 (5)0.3631 (4)0.0165 (14)
C80.6065 (9)0.4777 (5)0.4115 (4)0.0159 (13)
H8A0.61170.40330.40660.019*
C90.7352 (10)0.5264 (5)0.4795 (4)0.0227 (15)
H9A0.83020.48720.52110.027*
C100.7228 (9)0.6333 (6)0.4856 (4)0.0227 (15)
H10A0.80880.66770.53350.027*
O1W0.4472 (6)0.4697 (3)0.1733 (3)0.0163 (10)
H1WA0.539 (6)0.425 (3)0.185 (4)0.024*
H1WB0.499 (8)0.530 (2)0.179 (4)0.024*
O2W0.0576 (6)0.4839 (3)0.3208 (3)0.0150 (9)
H2WA−0.021 (7)0.433 (3)0.316 (4)0.022*
H2WB−0.004 (8)0.541 (2)0.320 (4)0.022*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ni10.0069 (4)0.0118 (5)0.0172 (5)0.0002 (3)0.0041 (3)0.0011 (3)
N10.009 (3)0.010 (3)0.022 (3)0.0056 (19)0.008 (2)0.009 (2)
N20.008 (3)0.018 (3)0.022 (3)0.003 (2)0.009 (2)0.001 (2)
N30.007 (3)0.014 (3)0.020 (3)−0.001 (2)0.001 (2)0.001 (2)
N40.011 (3)0.018 (3)0.021 (3)0.003 (2)0.009 (2)−0.003 (2)
N50.008 (2)0.017 (3)0.013 (3)0.001 (2)0.0042 (19)0.003 (2)
N60.010 (3)0.027 (3)0.022 (3)−0.006 (2)0.007 (2)−0.003 (2)
N70.014 (3)0.010 (3)0.023 (3)−0.001 (2)0.007 (2)−0.006 (2)
N80.010 (3)0.008 (2)0.025 (3)0.002 (2)0.003 (2)0.007 (2)
N90.020 (3)0.010 (2)0.027 (3)0.003 (2)0.020 (2)0.000 (2)
N100.013 (3)0.013 (3)0.016 (3)−0.001 (2)0.005 (2)−0.001 (2)
N110.007 (3)0.016 (3)0.019 (3)−0.001 (2)0.003 (2)0.000 (2)
N120.015 (3)0.023 (3)0.017 (3)−0.007 (2)0.007 (2)−0.009 (2)
C10.006 (3)0.013 (3)0.021 (3)−0.004 (2)0.009 (2)−0.002 (2)
C20.014 (3)0.013 (3)0.017 (3)0.004 (2)0.009 (2)0.004 (2)
C30.016 (3)0.023 (4)0.022 (3)0.001 (3)0.007 (3)0.001 (3)
C40.008 (3)0.032 (4)0.024 (3)0.003 (3)0.004 (2)0.006 (3)
C50.006 (3)0.030 (4)0.019 (3)−0.006 (2)0.006 (2)−0.004 (3)
C60.014 (3)0.006 (3)0.026 (3)−0.003 (2)0.017 (3)−0.002 (2)
C70.013 (3)0.026 (4)0.014 (3)−0.004 (3)0.008 (2)−0.003 (3)
C80.005 (3)0.020 (3)0.024 (3)0.002 (2)0.007 (2)0.002 (2)
C90.011 (3)0.033 (4)0.026 (4)0.005 (3)0.008 (3)0.004 (3)
C100.012 (3)0.037 (4)0.017 (3)−0.004 (3)0.002 (2)−0.006 (3)
O1W0.013 (2)0.015 (2)0.020 (2)−0.0012 (17)0.0040 (18)0.0015 (18)
O2W0.011 (2)0.009 (2)0.024 (2)−0.0030 (16)0.0043 (18)−0.0013 (17)
Geometric parameters (Å, °) top
Ni1—N12.057 (5)N11—C81.336 (8)
Ni1—N52.096 (5)N11—C71.349 (8)
Ni1—N72.051 (5)N12—C71.327 (7)
Ni1—N112.092 (5)N12—C101.355 (8)
Ni1—O1W2.087 (5)C1—C21.482 (8)
Ni1—O2W2.097 (5)C3—C41.386 (9)
N1—N21.323 (7)C3—H3A0.95
N1—C21.324 (8)C4—C51.394 (9)
N2—N31.327 (7)C4—H4A0.95
N3—N41.351 (7)C5—H5A0.95
N4—C21.324 (8)C6—C71.473 (8)
N5—C11.337 (8)C8—C91.368 (9)
N5—C31.341 (8)C8—H8A0.95
N6—C11.324 (7)C9—C101.366 (10)
N6—C51.339 (8)C9—H9A0.95
N7—C61.344 (8)C10—H10A0.95
N7—N81.351 (7)O1W—H1WA0.85 (2)
N8—N91.318 (7)O1W—H1WB0.84 (2)
N9—N101.348 (7)O2W—H2WA0.84 (2)
N10—C61.329 (7)O2W—H2WB0.85 (2)
N1—Ni1—N578.88 (19)N6—C1—C2120.5 (5)
N1—Ni1—N11100.25 (19)N5—C1—C2112.1 (5)
N1—Ni1—O1W90.80 (19)N4—C2—N1111.6 (5)
N1—Ni1—O2W89.12 (19)N4—C2—C1128.8 (5)
N5—Ni1—O2W90.91 (18)N1—C2—C1119.5 (5)
N7—Ni1—N1178.7 (2)N5—C3—C4120.2 (6)
N7—Ni1—N5101.22 (19)N5—C3—H3A119.9
N7—Ni1—N1179.63 (19)C4—C3—H3A119.9
N7—Ni1—O1W90.45 (19)C3—C4—C5117.3 (6)
N7—Ni1—O2W89.63 (19)C3—C4—H4A121.4
N11—Ni1—N5179.0 (2)C5—C4—H4A121.4
N11—Ni1—O2W88.52 (18)N6—C5—C4123.0 (6)
O1W—Ni1—N1191.29 (19)N6—C5—H5A118.5
O1W—Ni1—N589.28 (18)C4—C5—H5A118.5
O1W—Ni1—O2W179.78 (18)N10—C6—N7111.0 (5)
N2—N1—C2106.3 (5)N10—C6—C7129.4 (5)
N2—N1—Ni1140.3 (4)N7—C6—C7119.5 (5)
C2—N1—Ni1113.4 (4)N12—C7—N11127.7 (6)
N1—N2—N3108.4 (5)N12—C7—C6119.6 (6)
N2—N3—N4109.2 (5)N11—C7—C6112.6 (5)
C2—N4—N3104.5 (5)N11—C8—C9121.7 (6)
C1—N5—C3117.4 (5)N11—C8—H8A119.1
C1—N5—Ni1115.7 (4)C9—C8—H8A119.1
C3—N5—Ni1126.9 (4)C10—C9—C8117.9 (6)
C1—N6—C5114.7 (6)C10—C9—H9A121.1
C6—N7—N8106.1 (5)C8—C9—H9A121.1
C6—N7—Ni1112.7 (4)N12—C10—C9123.0 (6)
N8—N7—Ni1141.1 (4)N12—C10—H10A118.5
N9—N8—N7107.4 (5)C9—C10—H10A118.5
N8—N9—N10110.9 (5)Ni1—O1W—H1WA120 (5)
C6—N10—N9104.6 (5)Ni1—O1W—H1WB104 (5)
C8—N11—C7115.7 (5)H1WA—O1W—H1WB108 (3)
C8—N11—Ni1129.4 (4)Ni1—O2W—H2WA117 (4)
C7—N11—Ni1114.9 (4)Ni1—O2W—H2WB117 (4)
C7—N12—C10114.0 (6)H2WA—O2W—H2WB109 (3)
N6—C1—N5127.4 (5)
O1W—Ni1—N1—N294.4 (6)C5—N6—C1—C2176.6 (5)
N11—Ni1—N1—N23.0 (7)C3—N5—C1—N63.8 (9)
N5—Ni1—N1—N2−176.5 (7)Ni1—N5—C1—N6−176.0 (5)
O2W—Ni1—N1—N2−85.4 (6)C3—N5—C1—C2−175.9 (5)
O1W—Ni1—N1—C2−83.7 (4)Ni1—N5—C1—C24.4 (6)
N11—Ni1—N1—C2−175.1 (4)N3—N4—C2—N10.0 (7)
N5—Ni1—N1—C25.4 (4)N3—N4—C2—C1−175.3 (6)
O2W—Ni1—N1—C296.5 (4)N2—N1—C2—N40.6 (7)
C2—N1—N2—N3−0.9 (7)Ni1—N1—C2—N4179.3 (4)
Ni1—N1—N2—N3−179.1 (5)N2—N1—C2—C1176.3 (5)
N1—N2—N3—N40.9 (6)Ni1—N1—C2—C1−5.0 (7)
N2—N3—N4—C2−0.5 (6)N6—C1—C2—N4−4.4 (10)
N7—Ni1—N5—C1175.8 (4)N5—C1—C2—N4175.3 (6)
N1—Ni1—N5—C1−5.5 (4)N6—C1—C2—N1−179.3 (6)
O1W—Ni1—N5—C185.5 (4)N5—C1—C2—N10.4 (8)
O2W—Ni1—N5—C1−94.4 (4)C1—N5—C3—C4−1.2 (9)
N7—Ni1—N5—C3−3.9 (6)Ni1—N5—C3—C4178.5 (5)
N1—Ni1—N5—C3174.8 (6)N5—C3—C4—C5−1.6 (10)
O1W—Ni1—N5—C3−94.2 (5)C1—N6—C5—C4−0.2 (9)
O2W—Ni1—N5—C385.9 (5)C3—C4—C5—N62.3 (10)
O1W—Ni1—N7—C6−98.0 (4)N9—N10—C6—N70.9 (7)
N11—Ni1—N7—C6−6.8 (4)N9—N10—C6—C7176.5 (6)
N5—Ni1—N7—C6172.6 (4)N8—N7—C6—N10−0.7 (7)
O2W—Ni1—N7—C681.7 (4)Ni1—N7—C6—N10−178.4 (4)
O1W—Ni1—N7—N885.5 (7)N8—N7—C6—C7−176.9 (5)
N11—Ni1—N7—N8176.7 (7)Ni1—N7—C6—C75.4 (7)
N5—Ni1—N7—N8−3.9 (7)C10—N12—C7—N110.0 (9)
O2W—Ni1—N7—N8−94.7 (7)C10—N12—C7—C6−176.7 (6)
C6—N7—N8—N90.3 (6)C8—N11—C7—N12−1.0 (9)
Ni1—N7—N8—N9176.9 (5)Ni1—N11—C7—N12176.2 (5)
N7—N8—N9—N100.3 (6)C8—N11—C7—C6175.9 (5)
N8—N9—N10—C6−0.7 (6)Ni1—N11—C7—C6−6.9 (6)
N7—Ni1—N11—C8−175.5 (6)N10—C6—C7—N122.8 (10)
N1—Ni1—N11—C85.8 (6)N7—C6—C7—N12178.1 (6)
O1W—Ni1—N11—C8−85.3 (5)N10—C6—C7—N11−174.3 (6)
O2W—Ni1—N11—C894.6 (5)N7—C6—C7—N111.0 (8)
N7—Ni1—N11—C77.7 (4)C7—N11—C8—C90.5 (9)
N1—Ni1—N11—C7−171.0 (4)Ni1—N11—C8—C9−176.2 (5)
O1W—Ni1—N11—C797.9 (4)N11—C8—C9—C100.8 (10)
O2W—Ni1—N11—C7−82.2 (4)C7—N12—C10—C91.5 (9)
C5—N6—C1—N5−3.0 (9)C8—C9—C10—N12−1.9 (10)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1W—H1WA···N10i0.85 (2)1.97 (2)2.788 (7)162 (6)
O1W—H1WB···N3ii0.84 (2)1.97 (3)2.804 (7)167 (6)
O2W—H2WA···N9iii0.84 (2)1.97 (2)2.798 (6)170 (6)
O2W—H2WB···N4iv0.85 (2)1.97 (3)2.776 (7)160 (6)
Symmetry codes: (i) −x+1, y−1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1/2; (iii) −x, y−1/2, −z+1/2; (iv) −x, y+1/2, −z+1/2.
Table 1
Selected geometric parameters (Å, °) top
Ni1—N12.057 (5)Ni1—N112.092 (5)
Ni1—N52.096 (5)Ni1—O1W2.087 (5)
Ni1—N72.051 (5)Ni1—O2W2.097 (5)
N1—Ni1—N578.88 (19)N7—Ni1—O1W90.45 (19)
N1—Ni1—N11100.25 (19)N7—Ni1—O2W89.63 (19)
N1—Ni1—O1W90.80 (19)N11—Ni1—N5179.0 (2)
N1—Ni1—O2W89.12 (19)N11—Ni1—O2W88.52 (18)
N5—Ni1—O2W90.91 (18)O1W—Ni1—N1191.29 (19)
N7—Ni1—N1178.7 (2)O1W—Ni1—N589.28 (18)
N7—Ni1—N5101.22 (19)O1W—Ni1—O2W179.78 (18)
N7—Ni1—N1179.63 (19)
Table 2
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1W—H1WA···N10i0.85 (2)1.97 (2)2.788 (7)162 (6)
O1W—H1WB···N3ii0.84 (2)1.97 (3)2.804 (7)167 (6)
O2W—H2WA···N9iii0.84 (2)1.97 (2)2.798 (6)170 (6)
O2W—H2WB···N4iv0.85 (2)1.97 (3)2.776 (7)160 (6)
Symmetry codes: (i) −x+1, y−1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1/2; (iii) −x, y−1/2, −z+1/2; (iv) −x, y+1/2, −z+1/2.
references
References top

Bruker (1998). SMART (Version 5.051), SAINT (Version 5.01), SADABS (Version 2.03) and SHELXTL (Version 6.1). Bruker AXS Inc., Madison, Wisconsin, USA.

Jin, M.-F., Qiu, Y.-E. & Zhang, X.-L. (2007). Acta Cryst. E63, m2718–m2719.

Liu, J.-T. & Fan, S.-D. (2007a). Acta Cryst. E63, m1628–?.

Liu, J.-T. & Fan, S.-D. (2007b). Acta Cryst. E63, m1632–?.

Rodríguez, A. & Colacio, E. (2006). Chem. Commun. pp. 4140–4142.

Rodríguez, A., Kivekäsb, R. & Colacio, E. (2005). Chem. Commun. pp. 5228–5230.

Rodríguez, A., Salinas-Castillo, A., Galli, A. S., Masciocchi, N., Gutérrez-Zorrilla, J. M., Vitoriad, P. & Colacio, E. (2007). Dalton Trans. pp. 1821–1828.

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

Zhang, X.-L., Zhang, C.-L., Qiu, Y.-E. & An, N. (2007). Acta Cryst. E63, m2423–?.