Zoledronate complexes. III. Two zoledronate complexes with alkaline earth metals: [Mg(C₅H₉N₂O₇P₂)₂(H₂O)₂] and [Ca(C₅H₈N₂O₇P₂)(H₂O)]_n

Diaqua­bis[dihydrogen 1-hydr­oxy-2-(imidazol-3-ium-1-yl)ethyl­idene-1,1-diphospho­nato-κ²O,O′]magnesium(II), [Mg(C₅H₉N₂O₇P₂)₂(H₂O)₂], consists of isolated dimeric units built up around an inversion centre and tightly inter­connected by hy­drogen bonding. The Mg^II cation resides at the symmetry centre, surrounded in a rather regular octa­hedral geometry by two chelating zwitterionic zoledronate(1−) [or dihydrogen 1-hy­droxy-2-(imidazol-3-ium-1-yl)ethyl­idene-1,1-diphospho­n­ate] anions and two water mol­ecules, in a pattern already found in a few reported isologues where the anion is bound to transition metals (Co, Zn and Ni). catena-Poly[[aqua­calcium(II)]-μ₃-[hydrogen 1-hydr­oxy-2-(imidazol-3-ium-1-yl)ethyl­idene-1,1-diphospho­nato]-κ⁵O:O,O′:O′,O′′], [Ca(C₅H₈N₂O₇P₂)(H₂O)]_n, consists instead of a Ca^II cation in a general position, a zwitterionic zoledronate(2−) anion and a coordinated water mol­ecule. The geometry around the Ca^II atom, provided by six bis­phospho­nate O atoms and one water ligand, is that of a penta­gonal bipyramid with the Ca^II atom displaced by 0.19 Å out of the equatorial plane. These Ca^II coordination polyhedra are `threaded' by the 2₁ axis so that successive polyhedra share edges of their penta­gonal basal planes. This results in a strongly coupled rhomboidal Ca₂–O₂ chain which runs along [010]. These chains are in turn linked by an apical O atom from a –PO₃ group in a neighbouring chain. This O-atom, shared between chains, generates strong covalently bonded planar arrays parallel to (100). Finally, these sheets are linked by hydrogen bonds into a three-dimensional structure. Owing to the extreme affinity of zoledronic acid for bone tissue, in general, and with calcium as one of the major constituents of bone, it is expected that this structure will be useful in modelling some of the biologically inter­esting processes in which the drug takes part.

S1. Comment

Bisphosphonates (BPs) are an important class of osteotropic compounds that are effective in treating benign and malignant skeletal diseases characterized by enhanced osteoclast-mediated bone resorption (osteoporosis, Paget's disease and tumour-induced osteolysis; see, for instance, Green, 2005). BPs in general and zoledronic acid in particular act as a bone `shield' by stacking into the skeleton, achieving therapeutic concentrations and thus inhibiting bone resorption by cellular effects on osteoclasts. As part of a line of research on monovalent and divalent alkaline cation complexes with the zoledronate anion (hereafter Zol), we have recently reported the first two structures of this type, namely [K(Zol)(H₂O)].H₂O, (III) (Freire et al., 2010a), where all constituents (cation:anion: water_coord.: water_solv.) appeared in a rather simple 1:1:1:1 ratio, and [Na₃(Zol^0.5-)₂(Zol^-)₂(H₂O)₄].2H₂O, (IV) (Freire et al., 2010b), with a more complex 3:4:0:2 component ratio. A thorough introduction to zoledronate complexes has been included in the first of these reports, to which the interested reader is referred.

As a continuation of this series, we present herein the structures of two new zoledronate complexes, this time with divalent alkaline cations, viz. [Mg(Zol^-)₂(H₂O)₂], (I), and [Ca(Zol^2-)(H₂O)]_n, (II), the latter being a structure with indubitable interest from a biological point of view, a fact addressed in the concluding remarks of this paper.

Compound (I) consists of isolated dimeric units built up around an inversion centre (Fig. 1) and tightly interconnected by hydrogen bonding (Fig. 2). The Mg1 cation resides at an inversion centre, surrounded by two chelating Zol anions and two water molecules, of which only one is, of course, independent. This (1:2:2:0) cation:anion:water_coord.:watersolv. pattern has already been found in some transition metal zoledronate complexes, the present structure being isomorphous to the Co and Ni (Cao et al., 2007) and Zn (Freire & Vega, 2009) isologues, so that only a very brief discussion of points usually left aside will be included here. The rather regular octahedron built up around the cation presents an Mg—O range of 2.0393 to 2.1129 Å and a (cis)O—Mg1—O angular range of 90 ± 4.09°. Each zoledronate ligand displays its usual zwitterionic character, with a protonated imidazole⁺¹ ring and two singly protonated phosphonates^-1, with a resulting -1 total charge. This arrangement provides for due charge balance. P—OH distances [mean 1.575 (5) Å] are, as expected, significantly longer than P—O [mean 1.504 (5) Å], in agreement with what has been found in related structures (e.g. Coiro et al., 1989; Vega et al., 1996, 1998). The phosphonate groups present an `eclipsed' conformation when viewed in the P1···P2 direction (very nearly along the c axis), with an almost perfect O31—P1—C1—P2—O32 planar disposition (mean deviation from the plane = 0.012 Å).

The dimers interact actively through hydrogen bonding, with all available O—H and N—H taking part. The bond involving O1W—H1WB (Table 1, first entry) is intramolecular and provides cohesion to the dimer; those involving O1—H1O and O22—H22O (Table 1, second and third entries) link dimers together in a head-to-tail fashion (Fig. 2), defining chains parallel to [111]. The one involving O21—H21O links chains laterally to form planar arrays parallel to (110), which are finally connected with their upper/lower neighbours via the remaining hydrogen bonds involving N2—H2N and O1W—H1WA (Table 1, fourth and fifth entries). Fig. 2 presents a view down [001], where the (110) planes can be seen in projection. The interconnected dimeric cores are drawn in heavy lining, while in weak lining the interplanar connectors, viz. imidazole ring and apical water molecules, are shown.

Compound (II) is much more interesting in its structural features; it consists of a Ca^II cation, a zwitterionic Zol anion with a single H atom in one of its phosphonate groups and the usual protonated imidazole ring (thus providing the required two negative charges for due charge balance) and a coordinated water molecule (Fig. 3).This rather simple (1:1:1:0) cation:anion:water_coord.:watersolv. formulation expands into a tight two-dimensional network due to the coordination of the Ca1 cation by six ligating O atoms belonging to four different symmetry-related zoledronate units; there is in addition a seventh bond to a water ligand. This represents a new µ₄κ⁴ bonding mode for the Zol anion, shown schematically in Fig. 4 and labelled as `(i)', which should be considered an addendum to the binding modes presented in Freire et al. (2010a,b).

It is perhaps worth mentioning that the present coordination mode, as well as the one labelled `(f)' in the potassium complex reported in Freire et al. (2010a), display an unusual µ<sub>1</sub>κ<sup>2</sup> bidentate mode for one of the individual phosphonates, a rather unusual behaviour for this family of ligands, predicted as `unfavourable' by some pioneering calculations using molecular electrostatic potentials (Bjōrkroth et al., 1992) and confirmed as such by the very few examples which can be found in the literature, not only for zoledronate but for bisphosphonates in general as well.

There are four other reported seven-coordinated Ca bisphosphonates in the literature, one in Kontturi et al. (2002) and three in Kontturi et al. (2004); in all of them only four O atoms arising from bisphosphonate units are involved in the metal coordination, while the remaining three sites are occupied by water molecules. As expected, the result is a more open structure than the one found in (II), as is shown by the calculated densities [1.758, 1.918, 1.947 and 2.042 g cm^-3, respectively, against 2.058 g cm^-3 for (II)].

In compound (II) the geometry around Ca1 is that of a pentagonal bipyramid; the basal pentagon is essentially planar (mean deviation, 0.13 Å), but with [leaving] the calcium displaced from this mean plane by 0.19 Å. Six of the Ca—O bonds in the polyhedron have similar lengths in the range 2.3386 (17)–2.4393 (18) Å, but the seventh one, a basal bond, is much longer [Ca1—O32: 2.7605 (19) Å].

The bisphosphonate ligand in (II) differs from that in (I) in that only one of the phosphonate units carries an H atom and, as in (I), the P—OH distance is significantly longer than the remaining P—O distances [P1—O11 1.5915 (19) Å, against 1.4919 (17), 1.4993 (18) Å for the others]. The second phosphonate unit, containing no H, shows a much more even distribution of P—O distances, in the range 1.5174 (17)–1.5311 (19) Å, thus indicating marked delocalization of the negative charges. The overall geometry of the anion resembles that of structure (I), with an eclipsed setting of both phosphonate groups and a very planar disposition of the O31—P1—C1—P2—O32 group (mean deviation from the best plane: 0.011 Å).

Regarding coordination, the bisphosphonate groups act in a rather asymmetric fashion: five of the six PO₃ oxygens which bind the cation pertain to the same phosphonate Unit 2, distributed among four different symmetry-related zoledronate moieties (Table 3). These Ca coordination polyhedra are `threaded' by the 2₁ axis passing near Ca1 [Ca1: 0.54714 (3) 0.23153 (7) 0.18791 (4); 2₁: 0.50, x, 0.25], so that b/2 translations of the polyhedra end up with the juxtaposition of each other and the sharing of an edge of their pentagonal basal planes. This is mainly the result of atoms O22, O32 acting in a µ₂ chelating bridging mode which determine a chain of Ca₂O₂ links evolving along [010]. O21, the only basal oxygen not directly involved in the short bridges subtended by O22 and O32, takes part in a long O—P—C—P—O bridge joining neighbouring cations in the chain (Fig. 5). The result is a rhomboidal Ca₂—O₂ sequence, with a medium length Ca···Ca separation of 4.023 (1) Å along [010].

The two apical O atoms fulfil quite different roles: O1W is involved in hydrogen bonding (Table 4), while O12 at (x, -y + 1/2, z - 1/2) is part of a phosphonate group in a neighbouring chain, thus providing a covalent link along [001] between chains. This defines strongly coupled two-dimensional covalent structures parallel to (100), represented in hard lining in Fig. 6, where the chains are shown alongside, as short oblique motifs in heavy lining, interlinked by the P—O12—Ca bridges into broad horizontal chains. All the hydrogen bonds presented in Table 4 take place in this zone and are, in this sense, `interlayer', with the exception of the one involving N2—H2N, which serves to connect these broad planes into a three-dimensional structure. These interactions are shown in weak lining in Fig. 6.

As already noted above, zoledronic acid acts as a bone `shield' by stacking into the skeleton; the way it starts to do so is apparently by complexing the Ca cations in the bones, and in this respect the structure described here shows clear evidence of the avidity of zoledronate oxygens for the Ca cations. This is the reason why this latter Ca zoledronate complex is by far the most interesting of all the complexes of the anion reported so far, and it is expected that this structure will be found useful in modelling some of the biologically interesting processes in which the drug takes part.

Related literature

For related literature, see: Bjōrkroth, Perākylā, Pakkanen & Pohjala (1992); Cao et al. (2007); Coiro & Lamba (1989); Freire & Vega (2009); Freire et al. (2010a, 2010b); Green (2005); Kontturi et al. (2002, 2004); Vega et al. (1996, 1998).

S2. Experimental

Crystals of (I) and (II) were synthesized from a solution of zoledronic acid (from Gador Argentina S.A.) with a metal salt solution in a 2:1 stoichiometric ratio, using Mg(NO₃)₂ for (I) and CaCl₂ for (II). Crystals of (I) were grown at 353 K: the unperturbed solution was allowed to concentrate slowly and after a few days large, colourless blocks were obtained, suitable for single-crystal X-ray diffraction. Crystals of (II) were grown in a 45 ml Teflon-lined autoclave under hydrothermal conditions over a few days at 400 K.

S3. Refinement

The H atoms attached to O and N were found in a difference Fourier map, further idealized (O—H: 0.82, H···H: 1.32, N—H: 0.87 Å) and finally allowed to ride (see the discussion below about the O1—H1O pair). Those attached to C were placed at calculated positions (C—H: 0.93 Å; C—H₂: 0.97 Å) and allowed to ride. Displacement factors were taken as U(H)_isot = 1.2/1.5U_host.

Final difference maps for structure (I) disclosed some interesting features. The first one regards the behaviour of the refinement algorithm as applied to the P atoms. In spite of the refinement of (I) without any restraints or constraints, the least-squares procedure seemingly failed to provide an adequate anisotropic treatment for atoms P1 and P2: in the final difference maps both atoms appeared flanked by pairs of (opposite) positive and negative electron-density peaks of circa 1 e A^-3 in height, in a `crossed' arrangement typical of an insufficient anisotropic modelling of the displacement ellipsoids of both atoms. The second is the clear evidence of an (asymmetric) splitting in the O1—H1O···O32(1 - x, -y, 1 - z) hydrogen bond, with a hydrogen transfer from O1 towards O32 in the order of 10–15%, both sites displaying equilibrium positions with similar O—H distances (0.80–0.90 Å), as disclosed by the difference map. Owing to the very low occupancy, this splitting has not been included in the model, where atom H1O was assigned unit site occupancy.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988) for (I); CrysAlis PRO (Oxford Diffraction, 2009) for (II). Cell refinement: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988) for (I); CrysAlis PRO (Oxford Diffraction, 2009) for (II). Data reduction: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988) for (I); CrysAlis PRO (Oxford Diffraction, 2009) for (II). For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008). Molecular graphics: SHELXTL (Sheldrick, 2008) for (I); ORTEP-3 for Windows (Farrugia, 1997) for (II). Software used to prepare material for publication: SHELXTL (Sheldrick, 2008), PLATON (Spek, 2009) for (I); SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009) for (II).

Figures

	Fig. 1. Ellipsoid plot of (I), showing (in full lining and bonds) the asymmetric unit and (in empty ellipsoids and bonds) the symmetry-related part completing the dimer. Intra- and inter-dimeric interactions defining a hydrogen-bonded chain along [111] shown in broken lines. Symmetry codes: (i) -x + 2, -y + 1, -z + 2, (ii) -x + 1, -y, -z + 1, (iii) x - 1, y - 1, z - 1.
	Fig. 2. Packing view of (I) down [001], where the (110) planes can be seen (horizontally) in projection. The interconnected dimeric cores are drawn in heavy lining, while in weak lining the interplanar connectors, viz. imidazole ring and apical water molecules, are shown. Hydrogen bonds are shown in broken lines.
	Fig. 3. Ellipsoid plot of (II), showing (in full lining and bonds) the asymmetric unit and (in empty ellipsoids and bonds) the symmetry-related part completing the coordination polyhedron. Symmetry codes: (i) x, -y + 1/2, z - 1/2; (ii) -x + 1, y - 1/2, -z + 1/2; (iii) -x + 1, y + 1/2, -z + 1/2; (iv) x, -y + 1/2, z + 1/2.
	Fig. 4. The new µ4κ^4 coordination mode displayed by zoledronate in (II). This should be considered an addendum to Fig. 2 in Freire et al. (2010a,b).
	Fig. 5. Schematic representation of a chain in (II), with the imidazole groups removed for clarity. In double broken line the Ca—O21 bonds, linking chains laterally, to form two-dimensional structures. Symmetry code: (i) x, -y + 1/2, z - 1/2.
	Fig. 6. Packing diagram of (II) viewed along [100] and showing the planes in projection. In hard lining, the Ca bisphosphonste structure; in weak lining, the imidazole groups connecting two-dimensional structures via the N—H···O bond.

(I) Diaquabis[dihydrogen 1-hydroxy-2-(imidazol-3-ium-1-yl)ethylidene-1,1-diphosphonato- κ²O,O']magnesium(II)

Crystal data

[Mg(C5H9N2O7P2)2(H2O)2]	Z = 1
Mr = 602.51	F(000) = 310
Triclinic, P1	Dx = 1.863 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.4680 (15) Å	Cell parameters from 25 reflections
b = 8.4390 (17) Å	θ = 10–15°
c = 9.819 (2) Å	µ = 0.47 mm^−1
α = 105.11 (3)°	T = 294 K
β = 111.98 (3)°	Blocks, colourless
γ = 97.04 (3)°	0.28 × 0.22 × 0.20 mm
V = 537.0 (3) Å^3

Data collection

Rigaku AFC6 diffractometer	1875 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.037
Graphite monochromator	θmax = 26.0°, θmin = 2.4°
ω/2θ scans	h = −9→9
Absorption correction: ψ scan (North et al., 1968)	k = −1→10
Tmin = 0.78, Tmax = 0.83	l = −12→11
2554 measured reflections	3 standard reflections every 150 reflections
2103 independent reflections	intensity decay: 1%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.052	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.151	H-atom parameters constrained
S = 0.96	w = 1/[σ^2(Fo^2) + (0.1413P)^2 + 0.1155P] where P = (Fo^2 + 2Fc^2)/3
2103 reflections	(Δ/σ)max = 0.004
165 parameters	Δρmax = 0.93 e Å^−3
0 restraints	Δρmin = −0.94 e Å^−3

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Mg1	1.0000	0.5000	1.0000	0.0184 (3)
P1	0.62693 (7)	0.22640 (6)	0.97647 (6)	0.0178 (2)
P2	0.65600 (7)	0.22235 (6)	0.67057 (6)	0.0197 (2)
O1	0.3427 (2)	0.0437 (2)	0.69148 (19)	0.0262 (4)
H1O	0.3644	−0.0357	0.6306	0.029 (7)*
O11	0.7900 (2)	0.3859 (2)	1.05291 (17)	0.0228 (4)
O21	0.7234 (2)	0.0709 (2)	0.97587 (19)	0.0255 (4)
H21O	0.6476	−0.0157	0.9718	0.058 (10)*
O31	0.4782 (2)	0.2156 (2)	1.04578 (18)	0.0238 (4)
O12	0.8116 (2)	0.3864 (2)	0.76372 (18)	0.0263 (4)
O22	0.7636 (2)	0.0737 (2)	0.68485 (19)	0.0274 (4)
H22O	0.7063	−0.0197	0.6103	0.058 (11)*
O32	0.5337 (2)	0.1999 (2)	0.50211 (18)	0.0260 (4)
O1W	1.1158 (2)	0.2844 (2)	1.0064 (2)	0.0362 (5)
H1WA	1.2337	0.2882	1.0143	0.070 (12)*
H1WB	1.0337	0.1917	0.9419	0.12 (2)*
N1	0.2486 (3)	0.3477 (2)	0.6151 (2)	0.0239 (4)
N2	0.1445 (4)	0.4114 (3)	0.4051 (3)	0.0399 (6)
H2N	0.1310	0.4612	0.3390	0.048*
C1	0.4890 (3)	0.2043 (3)	0.7685 (2)	0.0201 (5)
C2	0.3747 (3)	0.3450 (3)	0.7703 (3)	0.0261 (5)
H2A	0.2916	0.3304	0.8242	0.031*
H2B	0.4703	0.4538	0.8293	0.031*
C3	0.0727 (4)	0.2299 (3)	0.5115 (3)	0.0335 (6)
H3	0.0094	0.1404	0.5290	0.040*
C4	0.0102 (4)	0.2702 (4)	0.3796 (3)	0.0415 (7)
H4	−0.1036	0.2122	0.2882	0.050*
C5	0.2879 (4)	0.4570 (3)	0.5488 (3)	0.0335 (6)
H5	0.3970	0.5499	0.5948	0.040*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg1	0.0120 (5)	0.0218 (5)	0.0182 (5)	0.0020 (4)	0.0007 (4)	0.0111 (4)
P1	0.0100 (3)	0.0230 (4)	0.0189 (4)	0.0034 (2)	0.0013 (3)	0.0123 (3)
P2	0.0136 (4)	0.0239 (4)	0.0166 (4)	0.0013 (2)	0.0009 (3)	0.0089 (3)
O1	0.0152 (8)	0.0250 (8)	0.0297 (9)	−0.0016 (6)	0.0030 (6)	0.0081 (7)
O11	0.0138 (8)	0.0276 (8)	0.0213 (8)	−0.0007 (6)	0.0020 (6)	0.0098 (6)
O21	0.0185 (8)	0.0280 (8)	0.0343 (9)	0.0086 (6)	0.0082 (7)	0.0205 (7)
O31	0.0162 (8)	0.0313 (8)	0.0277 (8)	0.0061 (6)	0.0085 (7)	0.0168 (7)
O12	0.0192 (8)	0.0302 (8)	0.0206 (8)	−0.0045 (6)	0.0005 (6)	0.0113 (7)
O22	0.0211 (8)	0.0310 (9)	0.0255 (8)	0.0092 (7)	0.0040 (7)	0.0097 (7)
O32	0.0213 (8)	0.0322 (8)	0.0172 (8)	0.0020 (7)	−0.0002 (6)	0.0114 (6)
O1W	0.0162 (8)	0.0300 (9)	0.0587 (12)	0.0068 (7)	0.0091 (8)	0.0188 (8)
N1	0.0182 (9)	0.0291 (10)	0.0258 (9)	0.0094 (7)	0.0042 (8)	0.0174 (8)
N2	0.0429 (14)	0.0516 (13)	0.0366 (12)	0.0202 (11)	0.0139 (10)	0.0333 (11)
C1	0.0134 (10)	0.0228 (10)	0.0198 (10)	0.0020 (8)	0.0014 (8)	0.0097 (8)
C2	0.0224 (11)	0.0304 (11)	0.0229 (11)	0.0110 (9)	0.0031 (9)	0.0128 (9)
C3	0.0218 (12)	0.0334 (13)	0.0382 (14)	0.0043 (10)	0.0010 (10)	0.0194 (11)
C4	0.0332 (14)	0.0480 (16)	0.0314 (13)	0.0092 (12)	−0.0038 (11)	0.0212 (12)
C5	0.0244 (12)	0.0398 (13)	0.0428 (14)	0.0109 (10)	0.0107 (11)	0.0276 (11)

Geometric parameters (Å, º)

Mg1—O11	2.0389 (16)	O22—H22O	0.8500
Mg1—O11^i	2.0389 (16)	O1W—H1WA	0.8501
Mg1—O12	2.0851 (19)	O1W—H1WB	0.8500
Mg1—O12^i	2.0851 (18)	N1—C5	1.323 (3)
Mg1—O1W	2.1132 (17)	N1—C3	1.379 (3)
Mg1—O1W^i	2.1132 (17)	N1—C2	1.470 (3)
P1—O11	1.4987 (17)	N2—C5	1.331 (3)
P1—O31	1.5096 (16)	N2—C4	1.360 (4)
P1—O21	1.5719 (16)	N2—H2N	0.8438
P1—C1	1.856 (2)	C1—C2	1.545 (3)
P2—O12	1.5011 (18)	C2—H2A	0.9700
P2—O32	1.5066 (17)	C2—H2B	0.9700
P2—O22	1.5785 (17)	C3—C4	1.352 (4)
P2—C1	1.852 (2)	C3—H3	0.9300
O1—C1	1.445 (2)	C4—H4	0.9300
O1—H1O	0.8500	C5—H5	0.9300
O21—H21O	0.8500
O11—Mg1—O11^i	180.0	P2—O22—H22O	115.9
O11—Mg1—O12	89.55 (7)	Mg1—O1W—H1WA	119.8
O11^i—Mg1—O12	90.45 (7)	Mg1—O1W—H1WB	114.0
O11—Mg1—O12^i	90.45 (7)	H1WA—O1W—H1WB	112.7
O11^i—Mg1—O12^i	89.55 (7)	C5—N1—C3	108.9 (2)
O12—Mg1—O12^i	180.000 (1)	C5—N1—C2	126.3 (2)
O11—Mg1—O1W	85.87 (7)	C3—N1—C2	124.8 (2)
O11^i—Mg1—O1W	94.13 (7)	C5—N2—C4	109.0 (2)
O12—Mg1—O1W	91.70 (8)	C5—N2—H2N	127.8
O12^i—Mg1—O1W	88.30 (8)	C4—N2—H2N	123.1
O11—Mg1—O1W^i	94.13 (7)	O1—C1—C2	107.37 (16)
O11^i—Mg1—O1W^i	85.87 (7)	O1—C1—P2	111.13 (14)
O12—Mg1—O1W^i	88.30 (8)	C2—C1—P2	112.30 (15)
O12^i—Mg1—O1W^i	91.70 (8)	O1—C1—P1	108.28 (14)
O1W—Mg1—O1W^i	180.000 (1)	C2—C1—P1	104.91 (14)
O11—P1—O31	115.86 (9)	P2—C1—P1	112.50 (11)
O11—P1—O21	108.77 (9)	N1—C2—C1	114.27 (17)
O31—P1—O21	109.91 (9)	N1—C2—H2A	108.7
O11—P1—C1	108.15 (10)	C1—C2—H2A	108.7
O31—P1—C1	108.05 (10)	N1—C2—H2B	108.7
O21—P1—C1	105.60 (10)	C1—C2—H2B	108.7
O12—P2—O32	115.70 (10)	H2A—C2—H2B	107.6
O12—P2—O22	107.67 (9)	C4—C3—N1	106.5 (2)
O32—P2—O22	110.64 (9)	C4—C3—H3	126.7
O12—P2—C1	107.78 (10)	N1—C3—H3	126.7
O32—P2—C1	109.47 (10)	C3—C4—N2	107.4 (2)
O22—P2—C1	104.99 (10)	C3—C4—H4	126.3
C1—O1—H1O	118.1	N2—C4—H4	126.3
P1—O11—Mg1	136.15 (10)	N1—C5—N2	108.2 (2)
P1—O21—H21O	112.9	N1—C5—H5	125.9
P2—O12—Mg1	133.46 (10)	N2—C5—H5	125.9
O31—P1—O11—Mg1	−166.48 (12)	O22—P2—C1—P1	60.13 (13)
O21—P1—O11—Mg1	69.16 (15)	O11—P1—C1—O1	175.23 (12)
C1—P1—O11—Mg1	−45.07 (16)	O31—P1—C1—O1	−58.64 (16)
O12—Mg1—O11—P1	28.74 (14)	O21—P1—C1—O1	58.93 (15)
O12^i—Mg1—O11—P1	−151.26 (14)	O11—P1—C1—C2	−70.36 (16)
O1W—Mg1—O11—P1	−63.00 (14)	O31—P1—C1—C2	55.77 (17)
O1W^i—Mg1—O11—P1	117.00 (14)	O21—P1—C1—C2	173.34 (14)
O32—P2—O12—Mg1	172.11 (11)	O11—P1—C1—P2	52.02 (13)
O22—P2—O12—Mg1	−63.55 (15)	O31—P1—C1—P2	178.14 (10)
C1—P2—O12—Mg1	49.24 (16)	O21—P1—C1—P2	−64.29 (13)
O11—Mg1—O12—P2	−30.85 (14)	C5—N1—C2—C1	−104.5 (3)
O11^i—Mg1—O12—P2	149.15 (14)	C3—N1—C2—C1	72.3 (3)
O1W—Mg1—O12—P2	55.00 (14)	O1—C1—C2—N1	−63.2 (2)
O1W^i—Mg1—O12—P2	−125.00 (14)	P2—C1—C2—N1	59.3 (2)
O12—P2—C1—O1	−176.06 (12)	P1—C1—C2—N1	−178.21 (16)
O32—P2—C1—O1	57.32 (16)	C5—N1—C3—C4	1.4 (3)
O22—P2—C1—O1	−61.48 (15)	C2—N1—C3—C4	−175.9 (2)
O12—P2—C1—C2	63.65 (16)	N1—C3—C4—N2	−1.1 (3)
O32—P2—C1—C2	−62.97 (17)	C5—N2—C4—C3	0.5 (3)
O22—P2—C1—C2	178.23 (14)	C3—N1—C5—N2	−1.1 (3)
O12—P2—C1—P1	−54.45 (14)	C2—N1—C5—N2	176.1 (2)
O32—P2—C1—P1	178.93 (10)	C4—N2—C5—N1	0.4 (3)

Symmetry code: (i) −x+2, −y+1, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1WB···O22	0.85	2.41	3.124 (3)	142
O1—H1O···O32^ii	0.85	2.06	2.904 (2)	170
O22—H22O···O32^ii	0.85	1.93	2.667 (3)	145
O1W—H1WA···O31^iii	0.85	1.94	2.744 (2)	158
O21—H21O···O31^iv	0.85	1.76	2.600 (2)	169
N2—H2N···O12^v	0.84	1.93	2.741 (3)	161

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

(II) catena-Poly[[aquacalcium(II)]-µ₃-[hydrogen 1-hydroxy-2-(imidazol-3-ium-1-yl)ethylidene-1,1-diphosphonato]- κ⁵O:O,O':O',O'']

Crystal data

[Ca(C5H8N2O7P2)(H2O)]	F(000) = 672
Mr = 328.17	Dx = 2.058 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2765 reflections
a = 13.7027 (15) Å	θ = 4.1–24.8°
b = 7.0429 (8) Å	µ = 0.93 mm^−1
c = 11.0040 (12) Å	T = 294 K
β = 94.007 (10)°	Needle, colourless
V = 1059.4 (2) Å^3	0.32 × 0.10 × 0.06 mm
Z = 4

Data collection

Oxford Diffraction Gemini CCD S Ultra diffractometer	2384 independent reflections
Radiation source: fine-focus sealed tube	1798 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ω scans, thick slices	θmax = 28.9°, θmin = 3.7°
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009)	h = −17→13
Tmin = 0.78, Tmax = 0.88	k = −9→9
4725 measured reflections	l = −13→12

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.085	H-atom parameters constrained
S = 0.96	w = 1/[σ^2(Fo^2) + (0.0528P)^2] where P = (Fo^2 + 2Fc^2)/3
2384 reflections	(Δ/σ)max = 0.001
168 parameters	Δρmax = 0.61 e Å^−3
0 restraints	Δρmin = −0.62 e Å^−3

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ca1	0.54714 (3)	0.23153 (7)	0.18791 (4)	0.01064 (14)
P1	0.24498 (4)	0.53194 (9)	0.46231 (6)	0.01130 (16)
P2	0.40077 (4)	0.24229 (8)	0.39689 (6)	0.00889 (15)
O1	0.24215 (12)	0.3527 (3)	0.25184 (15)	0.0166 (4)
H1O	0.2751	0.4471	0.2293	0.049 (11)*
O11	0.26377 (13)	0.4894 (3)	0.60406 (16)	0.0220 (4)
H11O	0.3168	0.4378	0.6317	0.055 (12)*
O21	0.31375 (13)	0.6826 (3)	0.42395 (17)	0.0189 (4)
O31	0.13857 (12)	0.5781 (3)	0.44686 (18)	0.0230 (5)
O12	0.42249 (12)	0.2215 (3)	0.53463 (16)	0.0162 (4)
O22	0.45794 (11)	0.3986 (2)	0.33891 (16)	0.0137 (4)
O32	0.41074 (12)	0.0599 (2)	0.32489 (17)	0.0184 (4)
O1W	0.64101 (12)	0.1067 (3)	0.36683 (16)	0.0166 (4)
H1WA	0.6506	0.1813	0.4272	0.043 (11)*
H1WB	0.6198	0.0009	0.3913	0.030 (9)*
N2	−0.02179 (15)	0.1110 (4)	0.2474 (2)	0.0250 (6)
H2N	−0.0606	0.0830	0.1828	0.073 (14)*
C1	0.26985 (16)	0.3135 (3)	0.3783 (2)	0.0108 (5)
C2	0.20962 (16)	0.1423 (4)	0.4152 (3)	0.0165 (5)
H2A	0.2390	0.0276	0.3855	0.020*
H2B	0.2126	0.1350	0.5034	0.020*
N1	0.10685 (14)	0.1489 (3)	0.3691 (2)	0.0155 (5)
C3	0.02814 (18)	0.1973 (4)	0.4328 (3)	0.0227 (6)
H3	0.0297	0.2384	0.5132	0.027*
C4	−0.05193 (19)	0.1737 (4)	0.3561 (3)	0.0246 (6)
H4	−0.1163	0.1961	0.3740	0.029*
C5	0.07431 (18)	0.0977 (4)	0.2567 (3)	0.0223 (6)
H5	0.1131	0.0591	0.1952	0.027*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca1	0.0107 (2)	0.0095 (3)	0.0118 (3)	0.00104 (18)	0.00127 (18)	−0.00016 (19)
P1	0.0087 (3)	0.0117 (3)	0.0136 (3)	0.0011 (2)	0.0013 (2)	−0.0007 (3)
P2	0.0082 (3)	0.0081 (3)	0.0105 (3)	0.0007 (2)	0.0014 (2)	0.0001 (2)
O1	0.0184 (9)	0.0179 (10)	0.0128 (10)	−0.0048 (8)	−0.0042 (7)	0.0016 (8)
O11	0.0264 (10)	0.0246 (10)	0.0149 (10)	0.0057 (8)	0.0006 (8)	0.0015 (8)
O21	0.0210 (9)	0.0134 (9)	0.0237 (11)	−0.0029 (7)	0.0112 (8)	−0.0039 (8)
O31	0.0104 (8)	0.0300 (11)	0.0282 (11)	0.0061 (8)	−0.0021 (7)	−0.0068 (9)
O12	0.0142 (8)	0.0210 (10)	0.0129 (10)	−0.0011 (7)	−0.0023 (7)	0.0037 (7)
O22	0.0147 (8)	0.0107 (9)	0.0164 (9)	0.0002 (7)	0.0057 (7)	0.0021 (7)
O32	0.0174 (9)	0.0129 (9)	0.0252 (11)	0.0028 (7)	0.0044 (8)	−0.0048 (8)
O1W	0.0201 (9)	0.0136 (9)	0.0157 (10)	−0.0034 (7)	−0.0017 (7)	−0.0018 (8)
N2	0.0174 (11)	0.0282 (14)	0.0285 (14)	−0.0044 (10)	−0.0041 (10)	−0.0031 (11)
C1	0.0107 (10)	0.0110 (12)	0.0103 (13)	−0.0003 (9)	−0.0010 (9)	−0.0003 (10)
C2	0.0111 (11)	0.0152 (13)	0.0226 (15)	−0.0003 (9)	−0.0033 (10)	0.0015 (11)
N1	0.0113 (9)	0.0150 (11)	0.0202 (12)	−0.0028 (8)	0.0005 (8)	−0.0011 (9)
C3	0.0192 (12)	0.0272 (16)	0.0226 (16)	−0.0031 (11)	0.0080 (11)	−0.0039 (12)
C4	0.0147 (12)	0.0251 (15)	0.0343 (18)	−0.0012 (11)	0.0048 (12)	−0.0015 (13)
C5	0.0167 (12)	0.0276 (16)	0.0227 (15)	−0.0049 (11)	0.0025 (11)	−0.0053 (12)

Geometric parameters (Å, º)

Ca1—O12^i	2.3386 (17)	O11—H11O	0.8500
Ca1—O22^ii	2.3637 (18)	O1W—H1WA	0.8500
Ca1—O21^ii	2.3655 (17)	O1W—H1WB	0.8499
Ca1—O32^iii	2.3902 (18)	N2—C5	1.317 (3)
Ca1—O22	2.4338 (18)	N2—C4	1.366 (4)
Ca1—O1W	2.4393 (18)	N2—H2N	0.8801
Ca1—O32	2.7605 (19)	C1—C2	1.532 (3)
P1—O31	1.4919 (17)	C2—N1	1.464 (3)
P1—O21	1.4993 (18)	C2—H2A	0.9700
P1—O11	1.5915 (19)	C2—H2B	0.9700
P1—C1	1.839 (3)	N1—C5	1.334 (3)
P2—O22	1.5174 (17)	N1—C3	1.370 (3)
P2—O32	1.5203 (18)	C3—C4	1.347 (4)
P2—O12	1.5311 (19)	C3—H3	0.9300
P2—C1	1.860 (2)	C4—H4	0.9300
O1—C1	1.443 (3)	C5—H5	0.9300
O1—H1O	0.8501
O12^i—Ca1—O22^ii	92.09 (6)	O22—P2—O32	109.03 (10)
O12^i—Ca1—O21^ii	102.70 (7)	O22—P2—O12	114.53 (10)
O22^ii—Ca1—O21^ii	78.95 (6)	O32—P2—O12	114.64 (11)
O12^i—Ca1—O32^iii	89.31 (6)	O22—P2—C1	106.28 (10)
O22^ii—Ca1—O32^iii	163.26 (6)	O32—P2—C1	106.94 (10)
O21^ii—Ca1—O32^iii	84.47 (6)	O12—P2—C1	104.71 (10)
O12^i—Ca1—O22	92.73 (6)	O22—P2—Ca1	48.55 (7)
O22^ii—Ca1—O22	123.58 (5)	O32—P2—Ca1	61.00 (7)
O21^ii—Ca1—O22	152.51 (6)	O12—P2—Ca1	129.02 (7)
O32^iii—Ca1—O22	72.98 (6)	C1—P2—Ca1	125.69 (8)
O12^i—Ca1—O1W	161.89 (6)	C1—O1—H1O	108.7
O22^ii—Ca1—O1W	75.67 (6)	P1—O11—H11O	120.5
O21^ii—Ca1—O1W	88.21 (6)	P1—O21—Ca1^iii	142.64 (11)
O32^iii—Ca1—O1W	106.29 (6)	P2—O12—Ca1^iv	141.45 (10)
O22—Ca1—O1W	83.39 (6)	P2—O22—Ca1^iii	139.53 (10)
O12^i—Ca1—O32	88.13 (6)	P2—O22—Ca1	103.58 (9)
O22^ii—Ca1—O32	67.59 (5)	Ca1^iii—O22—Ca1	113.96 (7)
O21^ii—Ca1—O32	145.22 (6)	P2—O32—Ca1^ii	151.53 (12)
O32^iii—Ca1—O32	129.15 (5)	P2—O32—Ca1	90.20 (8)
O22—Ca1—O32	56.45 (6)	Ca1^ii—O32—Ca1	102.47 (6)
O1W—Ca1—O32	74.96 (6)	Ca1—O1W—H1WA	116.9
O12^i—Ca1—P2	93.03 (5)	Ca1—O1W—H1WB	113.5
O22^ii—Ca1—P2	95.75 (4)	H1WA—O1W—H1WB	109.4
O21^ii—Ca1—P2	163.51 (5)	C5—N2—C4	108.5 (2)
O32^iii—Ca1—P2	100.84 (5)	C5—N2—H2N	126.3
O22—Ca1—P2	27.86 (4)	C4—N2—H2N	125.3
O1W—Ca1—P2	75.32 (4)	O1—C1—C2	107.23 (18)
O32—Ca1—P2	28.80 (4)	O1—C1—P1	106.21 (15)
O12^i—Ca1—Ca1^ii	97.64 (5)	C2—C1—P1	113.75 (17)
O22^ii—Ca1—Ca1^ii	33.56 (4)	O1—C1—P2	110.14 (15)
O21^ii—Ca1—Ca1^ii	109.81 (5)	C2—C1—P2	106.98 (16)
O32^iii—Ca1—Ca1^ii	162.10 (5)	P1—C1—P2	112.42 (12)
O22—Ca1—Ca1^ii	90.16 (4)	N1—C2—C1	114.0 (2)
O1W—Ca1—Ca1^ii	64.79 (4)	N1—C2—H2A	108.8
O32—Ca1—Ca1^ii	35.46 (4)	C1—C2—H2A	108.8
P2—Ca1—Ca1^ii	62.484 (19)	N1—C2—H2B	108.8
O12^i—Ca1—Ca1^iii	83.43 (5)	C1—C2—H2B	108.8
O22^ii—Ca1—Ca1^iii	154.61 (5)	H2A—C2—H2B	107.6
O21^ii—Ca1—Ca1^iii	126.43 (5)	C5—N1—C3	108.5 (2)
O32^iii—Ca1—Ca1^iii	42.07 (4)	C5—N1—C2	124.3 (2)
O22—Ca1—Ca1^iii	32.47 (4)	C3—N1—C2	127.1 (2)
O1W—Ca1—Ca1^iii	101.84 (5)	C4—C3—N1	106.6 (2)
O32—Ca1—Ca1^iii	87.25 (4)	C4—C3—H3	126.7
P2—Ca1—Ca1^iii	59.735 (19)	N1—C3—H3	126.7
Ca1^ii—Ca1—Ca1^iii	122.17 (2)	C3—C4—N2	107.8 (2)
O31—P1—O21	116.24 (11)	C3—C4—H4	126.1
O31—P1—O11	104.04 (11)	N2—C4—H4	126.1
O21—P1—O11	110.33 (11)	N2—C5—N1	108.7 (2)
O31—P1—C1	109.82 (11)	N2—C5—H5	125.7
O21—P1—C1	107.96 (10)	N1—C5—H5	125.7
O11—P1—C1	108.19 (11)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2N···O31^v	0.88	1.72	2.590 (3)	168
O1W—H1WB···O12^vi	0.85	1.88	2.722 (3)	173
O1W—H1WA···O21^vii	0.85	1.93	2.773 (3)	170
O1—H1O···O1W^iii	0.85	1.97	2.786 (2)	161
O11—H11O···O32^iv	0.85	2.41	3.066 (3)	135
O11—H11O···O12	0.85	2.40	3.017 (2)	130

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