PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of actaeInternational Union of Crystallographysearchopen accessarticle submissionjournal home pagethis article
 
Acta Crystallogr Sect E Struct Rep Online. 2009 November 1; 65(Pt 11): m1430–m1431.
Published online 2009 October 23. doi:  10.1107/S160053680904286X
PMCID: PMC2971399

Aquabis[1-hydroxy-2-(imidazol-3-ium-1-yl)-1,1′-ethylidenediphophonato-κ2 O,O′]zinc(II) dihydrate

Abstract

In the title complex, [Zn(C5H9NO7P2)2(H2O)]·2H2O, the zinc atom is coordinated by two zoledronate anions [zoledronate = (2-(1-imidazole)-1-hydr­oxy-1,1′-ethyl­idenediphophonate)] and one water mol­ecule. The coordination number is 5. There is one half-mol­ecule in the asymmetric unit, the zinc atom being located on a twofold rotation axis passing through the metal centre and the coordinating water O atom. The anion exists as a zwitterion with an overall charge of −1; the protonated nitro­gen in the ring has a positive charge and the two phospho­nates groups each have a single negative charge. Inter­molecular O—H(...)O hydrogen bonds link the mol­ecules. An N—H(...)O inter­action is also present.

Related literature

For general background to bis­phospho­nates, see: Fleisch et al. (1968 [triangle]); Green et al. (1994 [triangle]); Fleisch (2000 [triangle]); Ross et al. (2004 [triangle]); Smith (2005 [triangle]); Ralston et al. (1989 [triangle]); Reid et al. (2005 [triangle]); Rauch & Glorieux (2005 [triangle]); Chesnut et al. (2004 [triangle]). For structures of transition metal (Ni, Co and Cu) complexes with the zoledronate anion, see: Cao et al. (2007 [triangle], 2008 [triangle]). For metal complexes of other bis­phospho­nates (Etidronate and Pamidronate), see: Fernández et al. (2002 [triangle]); Li et al. (2008 [triangle]); Chen et al. (2008 [triangle]); Uchtman (1972 [triangle]). For a hexa­coordinated zinc(II)–zoledronate complex, see: Freire & Vega (2009 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-65-m1430-scheme1.jpg

Experimental

Crystal data

  • [Zn(C5H9N2O7P2)2(H2O)]·2H2O
  • M r = 661.58
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-m1430-efi1.jpg
  • a = 12.089 (2) Å
  • b = 9.858 (2) Å
  • c = 18.831 (4) Å
  • β = 95.09 (3)°
  • V = 2235.3 (8) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 1.48 mm−1
  • T = 293 K
  • 0.20 × 0.18 × 0.09 mm

Data collection

  • Rigaku AFC6 diffractometer
  • Absorption correction: ψ scan (North et al., 1968 [triangle]) T min = 0.75, T max = 0.87
  • 2847 measured reflections
  • 2208 independent reflections
  • 1528 reflections with I > 2σ(I)
  • R int = 0.054
  • 3 standard reflections every 150 reflections intensity decay: <3%

Refinement

  • R[F 2 > 2σ(F 2)] = 0.032
  • wR(F 2) = 0.096
  • S = 1.00
  • 2208 reflections
  • 167 parameters
  • H-atom parameters constrained
  • Δρmax = 0.35 e Å−3
  • Δρmin = −0.87 e Å−3

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988 [triangle]); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: MSC/AFC Diffractometer Control Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: SHELXTL (Sheldrick, 2008 [triangle]); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 [triangle]).

Table 1
Selected geometric parameters (Å, °)
Table 2
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S160053680904286X/bq2166sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S160053680904286X/bq2166Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

We acknowledge PICT 25409, the Spanish Research Council (CSIC) for providing us with a free-of-charge licence to use the CSD system (Allen, 2002 [triangle]) and Professor Judith Howard for the donation of a Rigaku AFC6S four-circle diffractometer. EF is a member of the research staff of Conicet. The authors are grateful to Laboratorios Gador for providing the zoledronic acid.

supplementary crystallographic information

Comment

The following work is part of a project directed to the preparation and characterization of coordination complexes obtained by the interaction among metals and organic molecules of relevant pharmacological interest like bisphosphonates. An informative introduction on bisphosphonates has been made in the previous paper (Freire & Vega, 2009). Although few metal derivatives of Zoledronic acid have been reported in CSD (Allen, 2002), an isostructural compound of copper has been synthesized (Cao et al., 2008).

So, we present herein the crystal structure of a Zinc-Zoledronate complex: monozinc dizoledronate trihydrate, (I), Zn.(H2O).2(P2O7N2C5H9).2H2O. In (I), as in the similar hexacoordinated compound (Freire & Vega, 2009), the zoledronate anion exists as a zwitterion with an overall charge of -1; the protonated nitrogen in the ring has a positive charge and the two phosphonates groups each have a single negative charge.

The coordination number of Zn is 5 (Fig. 1) and the resulting coordination polyhedron is a trigonal bipiramid defined by O21, O21A, O11, O11A and O1W. Atoms O11A and O21A are generated by the symmetry operation (1 - x, y, 3/2 - z). The equatorial plane is defined by O11, O11A and O1W, the apexes are defined by and O21 and O21A. The apical Zn—O distance is 2.041 (2) Å while in the equatorial plane the mean value for the Zn—O distance is 2.004 (4) Å. The coordination angles in the equatorial plane are a little turned aside from the expected 120 ° theoretically due to the "bite" of the ligand: O11—Zn—O11A 134.08 (15)°, O11—Zn—O1W and O11A—Zn—O1W are 112.96 (8) °. The angle between the line defined by O21 and O21A with the normal to the equatorial plane (O11, O11A, O1W and Zn1) is 2.3 °.

Considering the bisphosphonates groups, there are two distinct types of P—O bonds, as shown by the mean value in the following bond distances and angles: P—OH 1,576 (8), P - O 1.505 (5) Å, O—P—OH 109.4° (11), O—P—O 116.4° (14). The staggered conformation of PO3 groups in compound (II) is more prominent than in the hexacoordinated complex (Freire & Vega, 2009), the non bonded torsion angle O12—P1···P2 O22 is -16.1°. In (I), the imidazol ring is planar, maximum deviation from the L. S. mean plane is 0.0026 Å for C3, and it is not coplanar with C2, between the plane of the ring and the bond N1—C2 is 3.4 ° and C2 is 0.0837 Å far from the ring. The torsion angle C1—C2—N1—C3 is of -78.62 ° and it is possible to describe it like - Syn-Clinal (-sc).

Five hydrogen bonds, involving, H22, H1W, H1, H2WA and H2WB, provide intermolecular cohesion, defining a two-dimensional arrangement, while the three-dimensional net completes with two more hydrogen bonds, involving H2 from the aromatic ring and H12 from the bisphosphonate group (Fig. 2 and Table 2).

Experimental

Zoledronic Acid was obtained from Gador S. A. laboratory. Compound (II) was obtained by direct mix of a water solution of Zoledronic Acid and a water solution of ZnCl2. Colorless prismatic crystals were grown after a few days.

Refinement

The H atoms attached to O were found in a difference Fourier map, further idealized (O—H: 0.82 Å - 0.90 Å) and finally allowed to ride. Those attached to C and N were placed at calculated positions (C—H: 0.93 Å; C—H2: 0.97 Å; N—H2: 0.90 Å) and allowed to ride. Displacement factors were taken as U(H)isot = x.U(host), x: 1.2 (C—H); 1.5 (C—H2, N—H2, O—H).

Figures

Fig. 1.
: Molecular view of (I), showing the labeling scheme used. Hydrogen bonding is shown in dashed lines.
Fig. 2.
: Full packing diagram of (I).

Crystal data

[Zn(C5H9N2O7P2)2(H2O)]·2H2OF(000) = 1352
Mr = 661.58Dx = 1.966 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 42 reflections
a = 12.089 (2) Åθ = 8–25°
b = 9.858 (2) ŵ = 1.48 mm1
c = 18.831 (4) ÅT = 293 K
β = 95.09 (3)°Prism, colorless
V = 2235.3 (8) Å30.20 × 0.18 × 0.09 mm
Z = 4

Data collection

Rigaku AFC6 diffractometer1528 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.054
graphiteθmax = 26.0°, θmin = 2.2°
ω/2θ scansh = −1→14
Absorption correction: ψ scan (North et al., 1968)k = −1→12
Tmin = 0.75, Tmax = 0.87l = −23→23
2847 measured reflections3 standard reflections every 150 reflections
2208 independent reflections intensity decay: <3%

Refinement

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) = 0.096H-atom parameters constrained
S = 1.00w = 1/[σ2(Fo2) + (0.0521P)2 + 1.3378P] where P = (Fo2 + 2Fc2)/3
2208 reflections(Δ/σ)max = 0.001
167 parametersΔρmax = 0.35 e Å3
0 restraintsΔρmin = −0.87 e Å3

Special details

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)

xyzUiso*/Ueq
Zn10.50000.50532 (5)0.75000.02015 (15)
P10.64482 (6)0.41327 (8)0.61862 (4)0.01916 (19)
P20.76934 (6)0.48891 (8)0.75923 (4)0.01749 (19)
O10.71512 (19)0.6590 (2)0.64590 (11)0.0237 (5)
H10.71540.70930.68060.043 (12)*
O110.54208 (18)0.4259 (3)0.65807 (12)0.0299 (5)
O120.6205 (2)0.4826 (2)0.54319 (13)0.0288 (5)
H120.62710.43690.50750.050 (14)*
O130.68721 (19)0.2707 (2)0.61059 (12)0.0277 (5)
O210.66152 (17)0.5108 (2)0.79201 (11)0.0253 (5)
O220.85809 (18)0.5945 (2)0.79009 (12)0.0269 (5)
H220.83390.64910.81770.051 (14)*
O230.81904 (19)0.3498 (2)0.76479 (12)0.0280 (5)
O1W0.50000.7080 (4)0.75000.0727 (17)
H1W0.55650.75300.74700.109*
O2W0.6191 (2)0.3463 (3)0.42704 (13)0.0394 (6)
H2WA0.58990.39100.39370.059*
H2WB0.67900.31240.41960.059*
N10.8788 (2)0.5706 (3)0.56618 (13)0.0218 (5)
N20.8895 (2)0.7275 (3)0.48801 (15)0.0328 (7)
H20.89720.80600.46910.039*
C10.7536 (2)0.5248 (3)0.66243 (16)0.0183 (6)
C20.8707 (2)0.5064 (3)0.63530 (16)0.0216 (6)
H2A0.92620.54530.66980.026*
H2B0.88650.41030.63150.026*
C30.8930 (3)0.7035 (3)0.55705 (18)0.0278 (7)
H30.90340.76800.59310.033*
C40.8718 (3)0.6092 (4)0.45095 (19)0.0351 (8)
H40.86570.59910.40170.042*
C50.8649 (3)0.5096 (4)0.49990 (17)0.0282 (7)
H50.85300.41780.49070.034*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
Zn10.0189 (2)0.0212 (3)0.0206 (3)0.0000.00281 (18)0.000
P10.0201 (4)0.0188 (4)0.0187 (4)−0.0007 (3)0.0023 (3)−0.0026 (3)
P20.0181 (4)0.0171 (4)0.0172 (4)0.0010 (3)0.0010 (3)0.0012 (3)
O10.0348 (12)0.0148 (10)0.0211 (11)0.0063 (9)−0.0003 (9)0.0005 (9)
O110.0207 (11)0.0397 (14)0.0304 (13)−0.0072 (10)0.0080 (9)−0.0142 (11)
O120.0363 (13)0.0275 (12)0.0217 (11)0.0036 (10)−0.0033 (10)−0.0023 (10)
O130.0378 (13)0.0175 (11)0.0282 (11)0.0015 (10)0.0044 (10)−0.0035 (10)
O210.0190 (10)0.0362 (13)0.0208 (11)0.0021 (9)0.0029 (8)−0.0011 (10)
O220.0231 (11)0.0291 (13)0.0284 (12)−0.0052 (9)0.0019 (9)−0.0081 (11)
O230.0360 (13)0.0193 (11)0.0296 (12)0.0064 (9)0.0072 (10)0.0062 (9)
O1W0.025 (2)0.0195 (19)0.177 (6)0.0000.027 (3)0.000
O2W0.0535 (17)0.0414 (15)0.0233 (12)0.0094 (13)0.0041 (11)−0.0019 (11)
N10.0212 (12)0.0244 (13)0.0203 (13)−0.0008 (10)0.0051 (10)−0.0006 (12)
N20.0363 (16)0.0302 (15)0.0324 (15)−0.0009 (12)0.0062 (13)0.0132 (14)
C10.0207 (14)0.0144 (13)0.0197 (14)0.0035 (11)0.0020 (11)0.0013 (11)
C20.0193 (14)0.0239 (16)0.0217 (15)−0.0002 (12)0.0025 (12)0.0034 (13)
C30.0288 (17)0.0252 (16)0.0304 (18)−0.0040 (13)0.0073 (13)0.0004 (14)
C40.0333 (19)0.049 (2)0.0230 (17)0.0047 (16)0.0012 (14)0.0041 (17)
C50.0291 (17)0.0322 (18)0.0237 (16)−0.0001 (14)0.0044 (13)−0.0070 (15)

Geometric parameters (Å, °)

Zn1—O1W1.999 (4)O1W—H1W0.8200
Zn1—O112.006 (2)O2W—H2WA0.8200
Zn1—O11i2.006 (2)O2W—H2WB0.8200
Zn1—O21i2.041 (2)N1—C31.335 (4)
Zn1—O212.041 (2)N1—C51.382 (4)
P1—O131.508 (2)N1—C21.458 (4)
P1—O111.508 (2)N2—C31.318 (4)
P1—O121.580 (2)N2—C41.366 (5)
P1—C11.851 (3)N2—H20.8600
P2—O231.497 (2)C1—C21.558 (4)
P2—O211.506 (2)C2—H2A0.9700
P2—O221.569 (2)C2—H2B0.9700
P2—C11.850 (3)C3—H30.9300
O1—C11.427 (3)C4—C51.355 (5)
O1—H10.8200C4—H40.9300
O12—H120.8200C5—H50.9300
O22—H220.8200
O1W—Zn1—O11112.97 (8)H2WA—O2W—H2WB114.6
O1W—Zn1—O11i112.97 (7)C3—N1—C5108.5 (3)
O11—Zn1—O11i134.06 (15)C3—N1—C2124.1 (3)
O1W—Zn1—O21i88.48 (7)C5—N1—C2127.2 (3)
O11—Zn1—O21i89.03 (9)C3—N2—C4109.9 (3)
O11i—Zn1—O21i92.16 (9)C3—N2—H2125.0
O1W—Zn1—O2188.48 (7)C4—N2—H2125.0
O11—Zn1—O2192.16 (9)O1—C1—C2108.9 (2)
O11i—Zn1—O2189.03 (9)O1—C1—P2113.3 (2)
O21i—Zn1—O21176.96 (14)C2—C1—P2106.45 (19)
O13—P1—O11115.37 (14)O1—C1—P1104.41 (18)
O13—P1—O12110.54 (13)C2—C1—P1114.5 (2)
O11—P1—O12108.12 (14)P2—C1—P1109.42 (15)
O13—P1—C1111.36 (13)N1—C2—C1112.1 (2)
O11—P1—C1108.35 (13)N1—C2—H2A109.2
O12—P1—C1102.23 (13)C1—C2—H2A109.2
O23—P2—O21117.33 (14)N1—C2—H2B109.2
O23—P2—O22108.95 (14)C1—C2—H2B109.2
O21—P2—O22109.95 (13)H2A—C2—H2B107.9
O23—P2—C1104.47 (13)N2—C3—N1108.1 (3)
O21—P2—C1111.03 (13)N2—C3—H3126.0
O22—P2—C1104.20 (13)N1—C3—H3126.0
C1—O1—H1114.1C5—C4—N2106.7 (3)
P1—O11—Zn1137.76 (14)C5—C4—H4126.6
P1—O12—H12118.4N2—C4—H4126.6
P2—O21—Zn1132.07 (13)C4—C5—N1106.8 (3)
P2—O22—H22113.5C4—C5—H5126.6
Zn1—O1W—H1W122.7N1—C5—H5126.6
O13—P1—O11—Zn1114.0 (2)O13—P1—C1—O1162.06 (18)
O12—P1—O11—Zn1−121.6 (2)O11—P1—C1—O1−70.0 (2)
C1—P1—O11—Zn1−11.6 (3)O12—P1—C1—O144.0 (2)
O1W—Zn1—O11—P170.5 (2)O13—P1—C1—C243.0 (2)
O11i—Zn1—O11—P1−109.5 (2)O11—P1—C1—C2170.9 (2)
O21i—Zn1—O11—P1158.5 (2)O12—P1—C1—C2−75.0 (2)
O21—Zn1—O11—P1−18.7 (2)O13—P1—C1—P2−76.38 (17)
O23—P2—O21—Zn1−95.2 (2)O11—P1—C1—P251.53 (18)
O22—P2—O21—Zn1139.62 (18)O12—P1—C1—P2165.57 (14)
C1—P2—O21—Zn124.8 (2)C3—N1—C2—C178.5 (4)
O1W—Zn1—O21—P2−102.54 (19)C5—N1—C2—C1−96.1 (3)
O11—Zn1—O21—P210.4 (2)O1—C1—C2—N1−39.8 (3)
O11i—Zn1—O21—P2144.5 (2)P2—C1—C2—N1−162.3 (2)
O23—P2—C1—O1−175.2 (2)P1—C1—C2—N176.6 (3)
O21—P2—C1—O157.4 (2)C4—N2—C3—N10.6 (4)
O22—P2—C1—O1−60.9 (2)C5—N1—C3—N2−0.6 (4)
O23—P2—C1—C2−55.5 (2)C2—N1—C3—N2−176.1 (3)
O21—P2—C1—C2177.09 (19)C3—N2—C4—C5−0.3 (4)
O22—P2—C1—C258.8 (2)N2—C4—C5—N10.0 (4)
O23—P2—C1—P168.72 (17)C3—N1—C5—C40.4 (4)
O21—P2—C1—P1−58.67 (18)C2—N1—C5—C4175.7 (3)
O22—P2—C1—P1−176.99 (13)

Symmetry codes: (i) −x+1, y, −z+3/2.

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
O12—H12···O2W0.821.752.566 (3)171
O22—H22···O13ii0.821.842.645 (3)167
O2W—H2WA···O21iii0.822.382.990 (3)132
O2W—H2WB···O13iv0.821.942.758 (4)173
N2—H2···O12v0.862.112.917 (4)157
O1W—H1W···O23ii0.821.812.632 (3)177
O1—H1···O23ii0.821.802.581 (3)160

Symmetry codes: (ii) −x+3/2, y+1/2, −z+3/2; (iii) x, −y+1, z−1/2; (iv) −x+3/2, −y+1/2, −z+1; (v) −x+3/2, −y+3/2, −z+1.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BQ2166).

References

  • Allen, F. H. (2002). Acta Cryst. B58, 380–388. [PubMed]
  • Cao, D.-K., Li, Y.-Z. & Zheng, L.-M. (2007). Inorg. Chem.46, 7571–7578. [PubMed]
  • Cao, D.-K., Xie, X.-J., Li, Y.-Z. & Zheng, L.-M. (2008). Dalton Trans. pp. 5008–5015. [PubMed]
  • Chen, H., Sun, Z., Dong, D., Meng, L., Zheng, X., Zhu, Y., Zha, Y. & Zhang, J. (2008). J. Coord. Chem. 61, 1316–1324.
  • Chesnut, C. H. III, Skag, A., Christiansen, C., Recker, R., Stakkestad, J. A., Hoiseth, A., Felsenberg, D., Huss, H., Gilbride, J., Schimmer, R. C. & Delmas, P. D. (2004). J. Bone Miner. Res.19, 1241–1249. [PubMed]
  • Fernández, D., Vega, D. & Goeta, A. (2002). Acta Cryst. C58, m494–m497. [PubMed]
  • Fleisch, H. (2000). Bisphosphonates in Bone Disease. From the Laboratory to the Patient, 4th ed. New York: Academic Press.
  • Fleisch, H., Russell, R. G. G., Bisaz, S., Termine, J. D. & Posner, A. S. (1968). Calcif. Tissue Res.2, 49–59.
  • Freire, E. & Vega, D. R. (2009). Acta Cryst. E65, m1428–m1429. [PMC free article] [PubMed]
  • Green, J. R., Mueller, K. & Jaeggi, K. A. (1994). J. Bone Miner. Res.9, 745–751. [PubMed]
  • Li, G., Fan, Y., Zhang, T., Ge, T. & Hou, H. (2008). J. Coord. Chem.61, 540–549.
  • Molecular Structure Corporation (1988). MSC/AFC Diffractometer Control Software MSC, The Woodlands, Texas, USA.
  • North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359.
  • Ralston, S. H., Patel, U., Fraser, W. D., Gallacher, S. J., Dryburgh, F. J., Cowan, R. A. & Boyle, I. T. (1989). Lancet, 334, 1180–1182. [PubMed]
  • Rauch, F. & Glorieux, F. H. (2005). Am. J. Med. Genet. C. Semin. Med. Genet.139, 31–37. [PubMed]
  • Reid, I. R., Miller, P., Lyles, K., Fraser, W., Brown, J. P., Saidi, Y., Mesenbrink, P., Su, G., Pak, J., Zelenakas, K., Luchi, M., Richardson, P. & Hosking, D. (2005). N. Engl. J. Med.353, 898–908. [PubMed]
  • Ross, J. R., Saunders, Y., Edmonds, P. M., Wonderling, D., Normand, C. & Broadley, K. (2004). Health Technol. Assess.8, 1–176. [PubMed]
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Smith, M. R. (2005). Cancer Treat. Rev.31 (Suppl 3), 19–25. [PubMed]
  • Spek, A. L. (2009). Acta Cryst. D65, 148–155. [PMC free article] [PubMed]
  • Uchtman, V. A. (1972). J. Phys. Chem. 76, 1298–1304.

Articles from Acta Crystallographica Section E: Structure Reports Online are provided here courtesy of International Union of Crystallography