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In the crystal structure of the title compond, alternatively called poly[calcium(II)-di-μ-carboxymethylphosphonato], [Ca(C2H4O5P)2]n or [Ca(H2AP)2]n, one of the phosphonate O atoms of the phosphonocarboxylate monoanion lies nearly antiperiplanar (ap) to the carboxylic acid C atom. The phosphonate P atom is located −sc and +ac relative to the carboxylic acid O atoms. The overall structure has a layered architecture. The Ca2+ cations lie on a twofold axis and are bridged by the phosphonate O atoms to form chains along the c axis, giving layers parallel to (100). There are medium-strength O—H...O and C—H...O hydrogen-bonding interactions stabilizing the layers, and O—H...O hydrogen bonds connect adjacent layers.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102023302/fa1003sup1.cif
Contains datablocks caap, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102023302/fa1003Isup2.hkl
Contains datablock I

CCDC reference: 207991

Comment top

Metal phosphonates find application in many fields of chemistry, e.g. in catalysis and ion exchange (Bhardway et al., 1993; Alberti et al., 1996). The first structurally studied complex of phosphonoacetic acid (H3AP) was K4[Cu(C2H4O5P)2(H2O)]·6H2O (Afonin et al., 1998), in which the Cu2+ ion is five-coordinated by four O atoms of two bidentate chelating phosphonoacetate trianions and the O atom of the water molecule. Other crystal structures of M2+ phosphonoacetates (all with layered architectures) have been reported in the literature, namely [Al(O3PCH2COO)]·3H2O (Hix et al., 1998), [Mn3(O3PCH2COO)2] (Stock et al., 2000), and the isomorphous series [M(C2H4O5P)2(H2O)], with M = Mg (Charge?), MnII, CoII, ZnII and CuII (Ślepokura et al., 2003). Crystal structure studies of this last compound and of the title compound, (I), were undertaken as a continuation of a previous structural study of phosphonoacetic acid and its Na+, K+, Li+ and NH4+ salts (Lis, 1997). \sch

Phosphonoacetic acid may exist in four different forms, namely the tribasic acid, a monoanion (with one of the phosphonic O atoms deprotonated), a dianion (with phosphonic and carboxylic O atoms deprotonated) and a trianion (with all hydroxyl O atoms - two phosphonic and one carboxylic - deprotonated) (Lis, 1997). In (I), the anion occurs in the monoionized state. The molecular structure and the atom-numbering scheme for the monoanion are shown in Fig. 1.

The overall structure of the carboxymethylphosphonate monoanion is similar to that previously observed in phosphonoacetic acid and its M+ and M2+ salts (Lis, 1997; Ślepokura et al., 2003), with the carboxylic atom C1 lying nearly antiperiplanar -ap (trans) to the one of the phosphonate O atoms (O2) and nearly gauche (+sc and -sc) with respect to the remaining phosphonate O atoms (O1 and O3). The O2—P—C2—C1, O1—P—C2—C1 and O3—P—C2—C1 torsion angles are listed in Table 1.

The orientation of the phosphonate group in relation to the acetate group is one of the main points of interest in the structures of phosphonoacetic acid and its derivatives, and may be described by the above-mentioned torsion angles in combination with P—C2—C1—O4 and P—C2—C1—O5. The values of these last two angles show that the carboxylic O atoms are in positions -sc and +ac in relation to the P atom.

The conformation of the carboxymethylphosphonate monoanion in (I) lies between that found in free phosphonoacetic acid (Lis, 1997) and its M2+ salts (Ślepokura et al., 2003), and that found for the H3AP salts of monovalent cations (Lis, 1997) or in potassium, ammonium and dicyclohexylammonium salts of (2-oxopropyl)phosphonic acid (Mazurek & Lis, 1999). The values of the appropriate P—C2—C1—O4 and P—C2—C1—O5 torsion angles in the former group of compounds are about 50 and −132°, respectively; in the latter (for analogous P—C—C—O and P—C—C—C angles), regardless of the degree of ionization of the anion, the values are close to 90°, which means that the phosphonate group prefers a disposition almost perpendicular to the rest of molecule, while in the structure of (I) presented here, the relevant angles are −72.14 (9) and 107.20 (7)°, respectively.

In the phosphonate group of (I), a deformation from the ideal tetrahedral shape is observed, especially in the O2—P—O3 angle, in which the deprotonated O atoms are involved; the C2—P—O1(H) angle is the smallest among all phosphonate group angles, which is consistent with other monoionized phosphonate groups. The P—O1(H) bonds are longer than the P—O bonds.

The crystals of (I) are built up from Ca2+ ions and carboxymethylphosphonate monoanions, which act as bridging as well as chelating ligands. The Ca2+ cations are situated on a twofold axis and their eight-coordinate polyhedra are composed of the phosphonate O atoms only. Every metal cation is chelated by two carboxymethylphosphonate monoanions via atoms O1 and O2, and bridged by atom O2 from another monoanion, which in turn chelates an adjacent Ca2+ cation. Thus a chain is formed along the c axis (Fig. 2). The metal coordination sphere is completed by two O3 atoms from adjacent chains, forming layers parallel to (100). The shortest Ca···Ca distances are 3.938 (2) and 5.516 (2) Å within and between the chains, respectively.

On the whole, the structure of (I) fits into the known structural pattern for metal phosphonates. Many of them, as for (I) described here, are layered compounds, in which inorganic groups build up the layer backbone, while the organic parts protrude into the interlamellar spaces. The common structural motif, occurring here as well, is the planar network of tetra- or divalent metal ions (here Ca2+), knitted together by phosphonate O atoms above and below the layer plane (Cao et al., 1992, 1990; Dines & DiGiacomo, 1981; Hix, 1998). The structure of the layers is additionally stabilized by moderately strong O—H···O and C—H···O hydrogen bonds formed by both phosphonate and carboxylic moieties (Table 2). Situated in the interlamellar spaces, the carboxylic groups from adjacent layers are connected to each other via O—H···O hydrogen-bonding interactions (Fig. 3).

We have recently obtained crystals of a new magnesium salt of phosphonoacetic acid, in which a phase transition is observed at 230–240 K. The measurements for both phases were taken at 85 and 250 K and their structures will be published soon.

Experimental top

Crystalline calcium carboxymethylphosphonato was obtained from the reaction of commercially available (Aldrich) phosphonoacetic acid (aqueous solution) with solid CaCO3. The title polymeric bis(carboxymethylphosphonato)calcium(II) compound crystallizes in the form of colourless needles.

Refinement top

The H atoms were found in difference Fourier maps and were refined.

Computing details top

Data collection: Please provide missing information; cell refinement: Please provide missing information; data reduction: Please provide missing information; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Please provide missing information; software used to prepare material for publication: Please provide missing information.

Figures top
[Figure 1] Fig. 1. The molecular structure and atom-numbering scheme of the carboxymethylphosphonate monoanion in (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. The three-dimensional structure of (I). Displacement ellipsoids are drawn at the 50% probability level. For clarity, only one chain of Ca2+ cations connected via oxygen bridges is shown. From adjacent chains (above and below that shown), only O3 atoms are marked [symmetry code: (i) x, −y, 1/2 + z]. Dashed lines show intralayer O—H···O hydrogen bonds.
[Figure 3] Fig. 3. The layered structure of (I) viewed along [010]. Dashed lines show interlayer O—H···O hydrogen bonds.
poly[calcium(II)-di-µ-carboxymethylphosphonato] top
Crystal data top
[Ca(C2H4O5P)2]Z = 2
Mr = 318.12F(000) = 324
Monoclinic, P2/cDx = 2.085 Mg m3
Hall symbol: -P 2ycMo Kα radiation, λ = 0.71073 Å
a = 13.021 (3) ÅCell parameters from 6172 reflections
b = 5.516 (2) ŵ = 0.98 mm1
c = 7.358 (2) ÅT = 85 K
β = 106.50 (3)°Needle, colourless
V = 506.7 (3) Å30.30 × 0.30 × 0.05 mm
Data collection top
Kuma KM4 CCD κ-geometry
diffractometer
2437 independent reflections
Radiation source: fine-focus sealed tube2269 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.021
ω scansθmax = 37.4°, θmin = 3.7°
Absorption correction: gaussian
SHELXTL (Bruker, 1997)
h = 2221
Tmin = 0.782, Tmax = 0.950k = 99
8195 measured reflectionsl = 1012
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)] = 0.020Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.051All H-atom parameters refined
S = 1.13 w = 1/[σ2(Fo2) + (0.0243P)2 + 0.1327P]
where P = (Fo2 + 2Fc2)/3
2437 reflections(Δ/σ)max = 0.001
95 parametersΔρmax = 0.46 e Å3
0 restraintsΔρmin = 0.46 e Å3
Crystal data top
[Ca(C2H4O5P)2]V = 506.7 (3) Å3
Mr = 318.12Z = 2
Monoclinic, P2/cMo Kα radiation
a = 13.021 (3) ŵ = 0.98 mm1
b = 5.516 (2) ÅT = 85 K
c = 7.358 (2) Å0.30 × 0.30 × 0.05 mm
β = 106.50 (3)°
Data collection top
Kuma KM4 CCD κ-geometry
diffractometer
2437 independent reflections
Absorption correction: gaussian
SHELXTL (Bruker, 1997)
2269 reflections with I > 2σ(I)
Tmin = 0.782, Tmax = 0.950Rint = 0.021
8195 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0200 restraints
wR(F2) = 0.051All H-atom parameters refined
S = 1.13Δρmax = 0.46 e Å3
2437 reflectionsΔρmin = 0.46 e Å3
95 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ca0.50000.62721 (3)0.75000.00513 (4)
P0.343703 (14)0.17674 (3)0.56411 (2)0.00451 (5)
O10.33000 (5)0.29770 (11)0.74984 (8)0.00899 (10)
O20.43088 (4)0.31788 (10)0.51300 (8)0.00683 (9)
O30.36304 (4)0.09412 (10)0.58582 (8)0.00675 (9)
O40.10402 (5)0.08230 (12)0.42695 (11)0.01598 (12)
O50.06497 (6)0.29509 (13)0.49758 (12)0.02018 (14)
C10.12295 (6)0.13518 (14)0.43952 (10)0.00783 (11)
C20.21758 (6)0.24532 (13)0.39090 (10)0.00736 (11)
H10.3395 (15)0.224 (4)0.848 (3)0.037 (5)*
H50.0154 (15)0.218 (3)0.527 (3)0.037 (5)*
H210.2118 (11)0.411 (2)0.3881 (19)0.011 (3)*
H220.2218 (12)0.184 (3)0.265 (2)0.019 (3)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ca0.00590 (8)0.00496 (8)0.00459 (8)0.0000.00158 (6)0.000
P0.00465 (8)0.00449 (8)0.00446 (8)0.00022 (5)0.00139 (5)0.00005 (5)
O10.0142 (2)0.0082 (2)0.0052 (2)0.00283 (17)0.00380 (18)0.00008 (17)
O20.0064 (2)0.0070 (2)0.0074 (2)0.00191 (15)0.00231 (16)0.00024 (16)
O30.0081 (2)0.0048 (2)0.0073 (2)0.00050 (15)0.00212 (16)0.00026 (16)
O40.0128 (3)0.0112 (3)0.0270 (3)0.00421 (19)0.0106 (2)0.0045 (2)
O50.0165 (3)0.0109 (3)0.0407 (4)0.0004 (2)0.0205 (3)0.0008 (3)
C10.0054 (3)0.0101 (3)0.0075 (3)0.00027 (19)0.0010 (2)0.0009 (2)
C20.0056 (3)0.0092 (3)0.0071 (3)0.00015 (19)0.0015 (2)0.0018 (2)
Geometric parameters (Å, º) top
Ca—O2i2.3740 (8)P—C21.8098 (10)
Ca—O3ii2.4039 (8)O1—H10.81 (2)
Ca—O22.4229 (8)O4—C11.2229 (11)
Ca—O12.8639 (8)O5—C11.3091 (10)
Ca—Cai3.9376 (10)O5—H50.85 (2)
Ca—Caii5.5160 (11)C1—C21.5053 (10)
P—O21.5095 (6)C2—H210.920 (14)
P—O31.5160 (8)C2—H220.999 (15)
P—O11.5758 (7)
O2iii—Ca—O2i165.34 (3)O3—P—C2111.75 (3)
O2iii—Ca—O3ii85.94 (3)O1—P—C2102.63 (4)
O2i—Ca—O3ii84.70 (3)P—O1—Ca89.49 (3)
O3iv—Ca—O3ii100.50 (4)P—O1—H1122.3 (14)
O2iii—Ca—O2121.82 (2)Ca—O1—H1113.5 (13)
O2i—Ca—O269.66 (3)P—O2—Cai139.01 (4)
O3iv—Ca—O2151.99 (2)P—O2—Ca109.62 (3)
O3ii—Ca—O291.02 (3)Cai—O2—Ca110.34 (3)
O2—Ca—O2v90.47 (4)P—O3—Cavi139.51 (3)
O2iii—Ca—O167.01 (3)C1—O5—H5107.2 (13)
O2i—Ca—O1123.54 (2)O4—C1—O5124.27 (7)
O3iv—Ca—O1150.34 (2)O4—C1—C2122.61 (7)
O3ii—Ca—O186.71 (3)O5—C1—C2113.11 (7)
O2—Ca—O154.81 (3)C1—C2—P112.86 (5)
O2—Ca—O1v71.48 (3)C1—C2—H21109.9 (8)
O1—Ca—O1v101.21 (3)P—C2—H21106.1 (8)
O2—P—O3114.86 (3)C1—C2—H22110.4 (8)
O2—P—O1106.03 (4)P—C2—H22107.6 (8)
O3—P—O1112.47 (3)H21—C2—H22109.9 (12)
O2—P—C2108.24 (4)
O2—P—O1—Ca1.80 (3)O2v—Ca—O2—P65.32 (3)
O3—P—O1—Ca124.51 (3)O1—Ca—O2—P1.46 (2)
C2—P—O1—Ca115.25 (3)O1v—Ca—O2—P117.69 (4)
O2iii—Ca—O1—P178.13 (3)Cai—Ca—O2—P170.68 (5)
O2i—Ca—O1—P13.46 (3)Cavii—Ca—O2—P35.63 (3)
O3iv—Ca—O1—P159.57 (3)O2iii—Ca—O2—Cai169.82 (4)
O3ii—Ca—O1—P94.88 (3)O2i—Ca—O2—Cai0.03 (9)
O2—Ca—O1—P1.32 (2)O3iv—Ca—O2—Cai30.95 (5)
O2v—Ca—O1—P102.97 (3)O3ii—Ca—O2—Cai83.97 (3)
O1v—Ca—O1—P56.28 (3)O2v—Ca—O2—Cai124.00 (3)
Cai—Ca—O1—P7.38 (2)O1—Ca—O2—Cai169.22 (3)
Cavii—Ca—O1—P139.45 (3)O1v—Ca—O2—Cai71.63 (3)
O3—P—O2—Cai70.79 (6)Cavii—Ca—O2—Cai153.686 (18)
O1—P—O2—Cai164.36 (5)O2—P—O3—Cavi51.38 (6)
C2—P—O2—Cai54.84 (6)O1—P—O3—Cavi70.01 (6)
Ca—P—O2—Cai166.61 (7)C2—P—O3—Cavi175.17 (4)
O3—P—O2—Ca122.59 (4)Ca—P—O3—Cavi0.99 (6)
O1—P—O2—Ca2.25 (4)O4—C1—C2—P72.14 (9)
C2—P—O2—Ca111.77 (4)O5—C1—C2—P107.20 (7)
O2iii—Ca—O2—P0.86 (4)O2—P—C2—C1173.82 (5)
O2i—Ca—O2—P170.68 (5)O3—P—C2—C158.74 (6)
O3iv—Ca—O2—P158.37 (3)O1—P—C2—C162.00 (6)
O3ii—Ca—O2—P86.71 (4)Ca—P—C2—C1126.31 (5)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x, y+1, z; (iii) x, y+1, z+1/2; (iv) x+1, y+1, z+3/2; (v) x+1, y, z+3/2; (vi) x, y1, z; (vii) x+1, y+1, z+2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O3viii0.81 (2)1.83 (2)2.637 (2)173 (2)
O5—H5···O4ix0.85 (2)1.84 (2)2.687 (2)173 (2)
C2—H21···O1x0.92 (2)2.62 (2)3.231 (2)124 (1)
C2—H22···O3xi1.00 (2)2.60 (2)3.426 (2)140 (1)
C2—H22···O4xi1.00 (2)2.60 (2)3.432 (2)142 (1)
Symmetry codes: (viii) x, y, z+1/2; (ix) x, y, z+1; (x) x, y+1, z1/2; (xi) x, y, z1/2.

Experimental details

Crystal data
Chemical formula[Ca(C2H4O5P)2]
Mr318.12
Crystal system, space groupMonoclinic, P2/c
Temperature (K)85
a, b, c (Å)13.021 (3), 5.516 (2), 7.358 (2)
β (°) 106.50 (3)
V3)506.7 (3)
Z2
Radiation typeMo Kα
µ (mm1)0.98
Crystal size (mm)0.30 × 0.30 × 0.05
Data collection
DiffractometerKuma KM4 CCD κ-geometry
diffractometer
Absorption correctionGaussian
SHELXTL (Bruker, 1997)
Tmin, Tmax0.782, 0.950
No. of measured, independent and
observed [I > 2σ(I)] reflections
8195, 2437, 2269
Rint0.021
(sin θ/λ)max1)0.855
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.020, 0.051, 1.13
No. of reflections2437
No. of parameters95
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.46, 0.46

Computer programs: Please provide missing information, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997).

Selected geometric parameters (Å, º) top
Ca—O2i2.3740 (8)P—O31.5160 (8)
Ca—O3ii2.4039 (8)P—O11.5758 (7)
Ca—O22.4229 (8)P—C21.8098 (10)
Ca—O12.8639 (8)O4—C11.2229 (11)
Ca—Cai3.9376 (10)O5—C11.3091 (10)
Ca—Caii5.5160 (11)C1—C21.5053 (10)
P—O21.5095 (6)
O2—P—O3114.86 (3)O1—P—C2102.63 (4)
O2—P—O1106.03 (4)O4—C1—O5124.27 (7)
O3—P—O1112.47 (3)O4—C1—C2122.61 (7)
O2—P—C2108.24 (4)O5—C1—C2113.11 (7)
O3—P—C2111.75 (3)C1—C2—P112.86 (5)
O4—C1—C2—P72.14 (9)O3—P—C2—C158.74 (6)
O5—C1—C2—P107.20 (7)O1—P—C2—C162.00 (6)
O2—P—C2—C1173.82 (5)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O3iii0.81 (2)1.83 (2)2.637 (2)173 (2)
O5—H5···O4iv0.85 (2)1.84 (2)2.687 (2)173 (2)
C2—H21···O1v0.92 (2)2.62 (2)3.231 (2)124 (1)
C2—H22···O3vi1.00 (2)2.60 (2)3.426 (2)140 (1)
C2—H22···O4vi1.00 (2)2.60 (2)3.432 (2)142 (1)
Symmetry codes: (iii) x, y, z+1/2; (iv) x, y, z+1; (v) x, y+1, z1/2; (vi) x, y, z1/2.
 

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