metal-organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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catena-Poly[[(di­aqua­zinc)-μ-3-carb­­oxy­pyrazine-2-carboxyl­ato-κ4N1,O2;N4,O3] nitrate]

aInstitute of Nuclear Chemistry and Technology, ul. Dorodna 16, 03-195 Warszawa, Poland
*Correspondence e-mail: j.leciejewicz@ichtj.waw.pl

(Received 7 December 2011; accepted 15 December 2011; online 21 December 2011)

The crystal structure of the title compound, {[Zn(C6H3N2O4)(H2O)2]NO3}n, is built of zigzag cationic chains propagating in [010] with nitrate anions located in the space between the chains. The ZnII ion is coordinated by N and O atoms of two symmetry-related ligands in equatorial sites, and by two water O atoms at the axial sites of a distorted octa­hedron. One carboxyl­ate group of the ligand remains protonated, serving as a donor in a short intra­molecular O—H⋯O hydrogen bond. The coordinated water mol­ecules are donors and the nitrate O atoms act as acceptors in a network of O—H⋯O hydrogen bonds.

Related literature

For the crystal structures of ZnII complexes with pyrazine-2,3-dicarboxyl­ato and aqua ligands, see: Richard et al. (1974[Richard, P., Tranqui, D. & Bertaut, E. F. (1974). Acta Cryst. B30, 628-633.]); Ptasiewicz-Bąk & Leciejewicz (1999[Ptasiewicz-Bąk, H. & Leciejewicz, J. (1999). Pol. J. Chem. 73, 1887-1893.]); Gryz et al. (2005[Gryz, M., Starosta, W. & Leciejewicz, J. (2005). J. Coord. Chem. 58, 931-935.]).

[Scheme 1]

Experimental

Crystal data
  • [Zn(C6H3N2O4)(H2O)2]NO3

  • Mr = 330.52

  • Monoclinic, P 21 /n

  • a = 8.7431 (17) Å

  • b = 10.867 (2) Å

  • c = 11.412 (2) Å

  • β = 100.48 (3)°

  • V = 1066.2 (4) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 2.36 mm−1

  • T = 293 K

  • 0.20 × 0.19 × 0.15 mm

Data collection
  • Kuma KM-4 four-circle diffractometer

  • Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2008[Oxford Diffraction (2008). CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.]) Tmin = 0.636, Tmax = 0.747

  • 3232 measured reflections

  • 3101 independent reflections

  • 2397 reflections with I > 2σ(I)

  • Rint = 0.012

  • 3 standard reflections every 200 reflections intensity decay: 1.6%

Refinement
  • R[F2 > 2σ(F2)] = 0.032

  • wR(F2) = 0.097

  • S = 1.03

  • 3101 reflections

  • 192 parameters

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.81 e Å−3

  • Δρmin = −0.48 e Å−3

Table 1
Selected bond lengths (Å)

Zn1—O6 2.052 (2)
Zn1—O5 2.069 (2)
Zn1—O4i 2.0769 (18)
Zn1—O1 2.0816 (17)
Zn1—N1 2.1663 (18)
Zn1—N2i 2.1946 (19)
Symmetry code: (i) [-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}].

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
O6—H61⋯O13ii 0.84 (4) 1.90 (4) 2.732 (3) 176 (3)
O5—H52⋯O12iii 0.83 (4) 1.88 (4) 2.696 (3) 169 (4)
O6—H62⋯O11iii 0.72 (5) 2.04 (5) 2.758 (3) 175 (5)
O5—H51⋯O3ii 0.73 (6) 2.37 (5) 2.983 (3) 142 (5)
O5—H51⋯O11i 0.73 (6) 2.63 (6) 3.094 (4) 123 (5)
O2—H3⋯O3 1.20 (5) 1.22 (5) 2.404 (2) 170 (4)
Symmetry codes: (i) [-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]; (ii) [x-{\script{1\over 2}}, -y+{\script{3\over 2}}, z+{\script{1\over 2}}]; (iii) x-1, y, z.

Data collection: KM-4 Software (Kuma, 1996[Kuma (1996). KM-4 Software. Kuma Diffraction Ltd, Wrocław, Poland.]); cell refinement: KM-4 Software; data reduction: DATAPROC (Kuma, 2001[Kuma (2001). DATAPROC. Kuma Diffraction Ltd, Wrocław, Poland.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

The structures of three ZnII coordination compounds with pyrazine-2,3-dicarboxylate ligand (2,3-PZDC), each with a different molecular pattern were reported. In the triclinic structure of Zn(2,3-PZDC)(H2O)2.H2O (Richard et al., 1974) molecular ribbons are observed while the monoclinic Zn(2,3-PZDC)(H2O)3.H2O (Ptasiewicz-Bąk & Leciejewicz, 1999) shows a zigzag catenated molecular pattern. The monoclinic structure of (H3O)+2 [Zn(2,3-PZDC)2- is built of catenated doubly layered polyanions with hydronium cations in the interstitials (Gryz et al. 2005). The structure of the title compound is composed of zigzag molecular chains propagating along the crystal b axis in which ZnII ions are coordinated by N,O chelating groups of two singly deprotonated ligand molecules; their planes make a dihedral angle of 82.1 (1)° each to the other (Fig. 1). Two water O atoms complete the coordination of the ZnII ion to six, located at the apices of a distorted octahedron. O1, N1, O4i and O5 atoms form its basal plane with r.m.s. of 0.1408 (2) Å. Zn—O and Zn—N bond lengths are close to those observed in the structures of other Zn complexes with the title ligand (Richard, et al., 1974; Ptasiewicz-Bąk & Leciejewicz, 1999; Gryz, et al., 2005). A pyrazine ring is planar [r.m.s. 0.0146 (2) Å, the carboxylate groups C7/O1/O2 and C8/O3/O4 make with it dihedral angles of 4.8 (1)° and 171.9 (1)°, respectively. One of the carboxylate groups remains protonated and participates in a short, intra-molecular hydrogen bond of 2.404 (2) Å. Consequently, each building unit of the chain shows a singly positive charge which is compensated by a nitrate anion located in the space between chains (Fig. 2). Hydrogen bonds are observed between coordinated water molecules which act as donors and nitrate O atoms as acceptors (Table 2).

Related literature top

For the crystal structures of ZnII complexes with pyrazine-2,3-dicarboxylate and aqua ligands, see: Richard et al. (1974); Ptasiewicz-Bąk & Leciejewicz (1999); Gryz et al. (2005).

Experimental top

Single crystals of the title compound were found incidently in the course of an attempt to obtain dinuclear magnesium-zinc complex with the pyrazine-2,3-dicarboxylate ligand. A solution containing 2 mmols of pyrazine-2,3-dicarboxylic acid dihydrate, 1 mmol of magnesium nitrate dihydrate and a small excess over 1 mmol of zinc nitrate hexahydrate in 100 mL of doubly distilled water was boiled under reflux with stirring for 10 h. After cooling to room temperature, two drops of 95% hydrazine were added to the solution which was left to crystallise. Colourless single-crystal blocks of the title compound and crystals of Zn(H2O)6(NO3)2 were found in an unidentified polycrystalline material after evaporation to dryness. The crystals of the title complex were extracted, washed with ethanol and dried in air.

Refinement top

Water hydrogen atoms were located in a difference map and refined isotropically while H atoms attached to pyrazine-ring C atoms were located at calculated positions and treated as riding on the parent atoms with C—H=0.93 Å and Uiso(H)=1.2Ueq(C).

Computing details top

Data collection: KM-4 Software (Kuma, 1996); cell refinement: KM-4 Software (Kuma, 1996); data reduction: DATAPROC (Kuma, 2001); 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. A structural unit of the title compound with atom labelling scheme and 50% probability displacement ellipsoids. Symmetry code: (i) -x + 1/2, y + 1/2,-z + 1/2. An intramolecuular hydrogen bond is shown by dashed lines.
[Figure 2] Fig. 2. Packing diagram of the structure viewed along the c axis.
catena-Poly[[(diaquazinc)-µ-3-carboxypyrazine-2-carboxylato- κ4N1,O2;N4,O3] nitrate] top
Crystal data top
[Zn(C6H3N2O4)(H2O)2]NO3F(000) = 664
Mr = 330.52Dx = 2.059 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 25 reflections
a = 8.7431 (17) Åθ = 6–15°
b = 10.867 (2) ŵ = 2.36 mm1
c = 11.412 (2) ÅT = 293 K
β = 100.48 (3)°Blocks, colourless
V = 1066.2 (4) Å30.20 × 0.19 × 0.15 mm
Z = 4
Data collection top
Kuma KM-4 four-circle
diffractometer
2397 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.012
Graphite monochromatorθmax = 30.1°, θmin = 2.6°
profile data from ω/2θ scansh = 1012
Absorption correction: analytical
(CrysAlis RED; Oxford Diffraction, 2008)
k = 150
Tmin = 0.636, Tmax = 0.747l = 160
3232 measured reflections3 standard reflections every 200 reflections
3101 independent reflections intensity decay: 1.6%
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)] = 0.032Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.097H atoms treated by a mixture of independent and constrained refinement
S = 1.03 w = 1/[σ2(Fo2) + (0.0564P)2 + 0.8069P]
where P = (Fo2 + 2Fc2)/3
3101 reflections(Δ/σ)max = 0.001
192 parametersΔρmax = 0.81 e Å3
0 restraintsΔρmin = 0.48 e Å3
Crystal data top
[Zn(C6H3N2O4)(H2O)2]NO3V = 1066.2 (4) Å3
Mr = 330.52Z = 4
Monoclinic, P21/nMo Kα radiation
a = 8.7431 (17) ŵ = 2.36 mm1
b = 10.867 (2) ÅT = 293 K
c = 11.412 (2) Å0.20 × 0.19 × 0.15 mm
β = 100.48 (3)°
Data collection top
Kuma KM-4 four-circle
diffractometer
2397 reflections with I > 2σ(I)
Absorption correction: analytical
(CrysAlis RED; Oxford Diffraction, 2008)
Rint = 0.012
Tmin = 0.636, Tmax = 0.7473 standard reflections every 200 reflections
3232 measured reflections intensity decay: 1.6%
3101 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0320 restraints
wR(F2) = 0.097H atoms treated by a mixture of independent and constrained refinement
S = 1.03Δρmax = 0.81 e Å3
3101 reflectionsΔρmin = 0.48 e Å3
192 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
Zn10.00406 (3)0.82559 (2)0.26307 (2)0.02503 (9)
C70.0503 (2)0.68275 (19)0.06020 (18)0.0235 (4)
C20.1549 (2)0.61605 (18)0.16261 (17)0.0212 (4)
N10.1442 (2)0.66517 (17)0.26888 (16)0.0255 (4)
C30.2546 (2)0.51569 (19)0.15702 (18)0.0214 (4)
C80.3008 (3)0.45650 (19)0.04721 (19)0.0247 (4)
C60.2221 (3)0.6151 (2)0.36834 (19)0.0303 (5)
H60.21530.64950.44180.036*
O50.1653 (2)0.96368 (18)0.2120 (2)0.0403 (4)
N20.3300 (2)0.46525 (17)0.25858 (16)0.0246 (3)
O30.2334 (2)0.48857 (16)0.05626 (14)0.0314 (3)
O40.4046 (2)0.37756 (16)0.06479 (15)0.0313 (3)
O20.0421 (2)0.64513 (17)0.04597 (14)0.0323 (4)
O10.02615 (19)0.77131 (15)0.08585 (14)0.0295 (3)
O60.1700 (2)0.71769 (19)0.3183 (2)0.0373 (4)
C50.3133 (3)0.5120 (2)0.36293 (19)0.0294 (4)
H50.36340.47520.43300.035*
O110.5234 (3)0.7166 (3)0.2043 (2)0.0568 (6)
O120.5562 (3)0.8786 (3)0.1012 (3)0.0758 (9)
O130.3449 (2)0.7771 (2)0.05949 (19)0.0463 (5)
N30.4762 (2)0.7915 (2)0.1237 (2)0.0366 (5)
H610.166 (4)0.723 (3)0.392 (3)0.035 (8)*
H520.256 (5)0.946 (4)0.181 (4)0.056 (11)*
H620.251 (6)0.722 (4)0.289 (4)0.081 (16)*
H510.165 (6)1.002 (5)0.265 (5)0.095 (19)*
H30.143 (5)0.574 (4)0.056 (4)0.088 (15)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Zn10.02357 (14)0.02086 (13)0.02998 (14)0.00042 (9)0.00303 (9)0.00081 (9)
C70.0212 (9)0.0232 (9)0.0241 (9)0.0025 (7)0.0014 (7)0.0015 (7)
C20.0199 (8)0.0202 (8)0.0224 (9)0.0013 (7)0.0010 (7)0.0010 (7)
N10.0253 (8)0.0249 (9)0.0249 (8)0.0031 (7)0.0006 (7)0.0020 (6)
C30.0205 (9)0.0197 (8)0.0234 (8)0.0014 (7)0.0022 (7)0.0003 (7)
C80.0260 (10)0.0236 (9)0.0246 (9)0.0015 (7)0.0047 (7)0.0003 (7)
C60.0353 (11)0.0328 (11)0.0214 (9)0.0080 (9)0.0016 (8)0.0015 (8)
O50.0317 (10)0.0276 (9)0.0589 (13)0.0062 (7)0.0010 (9)0.0050 (8)
N20.0231 (8)0.0236 (8)0.0260 (8)0.0020 (6)0.0013 (6)0.0012 (6)
O30.0360 (9)0.0348 (9)0.0231 (7)0.0068 (7)0.0041 (6)0.0002 (6)
O40.0353 (9)0.0296 (8)0.0297 (8)0.0079 (7)0.0075 (7)0.0003 (6)
O20.0345 (9)0.0363 (9)0.0233 (7)0.0070 (7)0.0022 (6)0.0015 (6)
O10.0291 (8)0.0264 (8)0.0295 (8)0.0060 (6)0.0035 (6)0.0009 (6)
O60.0315 (10)0.0400 (10)0.0393 (11)0.0078 (8)0.0041 (8)0.0034 (8)
C50.0318 (11)0.0309 (11)0.0236 (9)0.0057 (9)0.0004 (8)0.0014 (8)
O110.0473 (12)0.0708 (16)0.0467 (12)0.0080 (11)0.0060 (9)0.0132 (11)
O120.0526 (15)0.0659 (17)0.100 (2)0.0293 (13)0.0098 (14)0.0186 (16)
O130.0259 (9)0.0682 (14)0.0428 (10)0.0089 (9)0.0006 (8)0.0042 (10)
N30.0265 (10)0.0452 (12)0.0379 (11)0.0069 (9)0.0052 (8)0.0012 (9)
Geometric parameters (Å, º) top
Zn1—O62.052 (2)C6—C51.382 (3)
Zn1—O52.069 (2)C6—H60.9300
Zn1—O4i2.0769 (18)O5—H520.83 (4)
Zn1—O12.0816 (17)O5—H510.73 (6)
Zn1—N12.1663 (18)N2—C51.327 (3)
Zn1—N2i2.1946 (19)N2—Zn1ii2.1947 (19)
C7—O11.237 (3)O3—H31.22 (5)
C7—O21.268 (3)O4—Zn1ii2.0769 (18)
C7—C21.529 (3)O2—H31.20 (5)
C2—N11.344 (3)O6—H610.84 (4)
C2—C31.405 (3)O6—H620.72 (5)
N1—C61.330 (3)C5—H50.9300
C3—N21.342 (3)O11—N31.241 (3)
C3—C81.527 (3)O12—N31.230 (3)
C8—O41.238 (3)O13—N31.254 (3)
C8—O31.269 (3)
O6—Zn1—O590.99 (9)C2—C3—C8128.54 (18)
O6—Zn1—O4i93.59 (8)O4—C8—O3122.9 (2)
O5—Zn1—O4i102.46 (9)O4—C8—C3117.00 (19)
O6—Zn1—O1101.00 (8)O3—C8—C3120.06 (19)
O5—Zn1—O189.65 (9)N1—C6—C5120.2 (2)
O4i—Zn1—O1160.90 (7)N1—C6—H6119.9
O6—Zn1—N189.06 (8)C5—C6—H6119.9
O5—Zn1—N1164.96 (9)Zn1—O5—H52120 (3)
O4i—Zn1—N192.55 (7)Zn1—O5—H51107 (4)
O1—Zn1—N175.58 (7)H52—O5—H51110 (5)
O6—Zn1—N2i166.71 (8)C5—N2—C3120.11 (19)
O5—Zn1—N2i85.27 (8)C5—N2—Zn1ii123.90 (15)
O4i—Zn1—N2i74.86 (7)C3—N2—Zn1ii115.27 (14)
O1—Zn1—N2i91.74 (7)C8—O3—H3114 (2)
N1—Zn1—N2i97.85 (7)C8—O4—Zn1ii120.67 (15)
O1—C7—O2122.53 (19)C7—O2—H3113 (2)
O1—C7—C2117.50 (19)C7—O1—Zn1119.46 (14)
O2—C7—C2119.96 (19)Zn1—O6—H61112 (2)
N1—C2—C3119.66 (18)Zn1—O6—H62121 (4)
N1—C2—C7111.79 (18)H61—O6—H62108 (4)
C3—C2—C7128.54 (18)N2—C5—C6120.6 (2)
C6—N1—C2119.93 (19)N2—C5—H5119.7
C6—N1—Zn1124.51 (15)C6—C5—H5119.7
C2—N1—Zn1115.56 (14)O12—N3—O11122.2 (2)
N2—C3—C2119.29 (18)O12—N3—O13118.0 (3)
N2—C3—C8112.05 (18)O11—N3—O13119.8 (2)
Symmetry codes: (i) x+1/2, y+1/2, z+1/2; (ii) x+1/2, y1/2, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O6—H61···O13iii0.84 (4)1.90 (4)2.732 (3)176 (3)
O5—H52···O12iv0.83 (4)1.88 (4)2.696 (3)169 (4)
O6—H62···O11iv0.72 (5)2.04 (5)2.758 (3)175 (5)
O5—H51···O3iii0.73 (6)2.37 (5)2.983 (3)142 (5)
O5—H51···O11i0.73 (6)2.63 (6)3.094 (4)123 (5)
O2—H3···O31.20 (5)1.22 (5)2.404 (2)170 (4)
Symmetry codes: (i) x+1/2, y+1/2, z+1/2; (iii) x1/2, y+3/2, z+1/2; (iv) x1, y, z.

Experimental details

Crystal data
Chemical formula[Zn(C6H3N2O4)(H2O)2]NO3
Mr330.52
Crystal system, space groupMonoclinic, P21/n
Temperature (K)293
a, b, c (Å)8.7431 (17), 10.867 (2), 11.412 (2)
β (°) 100.48 (3)
V3)1066.2 (4)
Z4
Radiation typeMo Kα
µ (mm1)2.36
Crystal size (mm)0.20 × 0.19 × 0.15
Data collection
DiffractometerKuma KM-4 four-circle
diffractometer
Absorption correctionAnalytical
(CrysAlis RED; Oxford Diffraction, 2008)
Tmin, Tmax0.636, 0.747
No. of measured, independent and
observed [I > 2σ(I)] reflections
3232, 3101, 2397
Rint0.012
(sin θ/λ)max1)0.705
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.032, 0.097, 1.03
No. of reflections3101
No. of parameters192
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.81, 0.48

Computer programs: KM-4 Software (Kuma, 1996), DATAPROC (Kuma, 2001), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Selected bond lengths (Å) top
Zn1—O62.052 (2)Zn1—O12.0816 (17)
Zn1—O52.069 (2)Zn1—N12.1663 (18)
Zn1—O4i2.0769 (18)Zn1—N2i2.1946 (19)
Symmetry code: (i) x+1/2, y+1/2, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O6—H61···O13ii0.84 (4)1.90 (4)2.732 (3)176 (3)
O5—H52···O12iii0.83 (4)1.88 (4)2.696 (3)169 (4)
O6—H62···O11iii0.72 (5)2.04 (5)2.758 (3)175 (5)
O5—H51···O3ii0.73 (6)2.37 (5)2.983 (3)142 (5)
O5—H51···O11i0.73 (6)2.63 (6)3.094 (4)123 (5)
O2—H3···O31.20 (5)1.22 (5)2.404 (2)170 (4)
Symmetry codes: (i) x+1/2, y+1/2, z+1/2; (ii) x1/2, y+3/2, z+1/2; (iii) x1, y, z.
 

References

First citationGryz, M., Starosta, W. & Leciejewicz, J. (2005). J. Coord. Chem. 58, 931–935.  Web of Science CSD CrossRef CAS Google Scholar
First citationKuma (1996). KM-4 Software. Kuma Diffraction Ltd, Wrocław, Poland.  Google Scholar
First citationKuma (2001). DATAPROC. Kuma Diffraction Ltd, Wrocław, Poland.  Google Scholar
First citationOxford Diffraction (2008). CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.  Google Scholar
First citationPtasiewicz-Bąk, H. & Leciejewicz, J. (1999). Pol. J. Chem. 73, 1887–1893.  Google Scholar
First citationRichard, P., Tranqui, D. & Bertaut, E. F. (1974). Acta Cryst. B30, 628–633.  CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar

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