Poly[[[mu]-(1-aza­nium­yl­ethane-1,1-di­yl)bis­(hydrogen phosphon­ato)]sodium]: a powder X-ray diffraction study

The title two-dimensional coordination polymer, [Na(C₂H₈NO₆P₂)]_n, was characterized using powder X-ray diffraction data and its structure refined using the Rietveld method. The asymmetric unit contains one Na⁺ cation and one (1-azan­ium­yl­ethane-1,1-di­yl)bis­(hydrogen phosphon­ate) anion. The central Na⁺ cation exhibits distorted octa­hedral coordination geometry involving two deprotonated O atoms, two hy­droxy O atoms and two double-bonded O atoms of the bis­phosphon­ate anion. Pairs of sodium-centred octa­hedra share edges and the pairs are in turn connected to each other by the biphosphon­ate anion to form a two-dimensional network parallel to the (001) plane. The polymeric layers are connected by strong O-H...O hydrogen bonding between the hy­droxy group and one of the free O atoms of the bis­phosphon­ate anion to generate a three-dimensional network. Further stabilization of the crystal structure is achived by N-H...O and O-H...O hydrogen bonding.

S1. Comment

Bisphospho­nates are biologically relevant therapeutics for bone disorders and cancer (Abdou & Shaddy, 2009; Fleisch, 1998). These compounds exhibit specific affinity towards bone, which makes them an excellent therapeutic for bone-resorption diseases (especially osteoporosis, Paget's disease, tumour-induced osteolysis and hypercalcaemia originating from malignancy) by inhibition of farnesyl diphosphate synthase, and for bone tumours caused by metastatic breast tumours (Body et al., 1998; Russell & Rogers, 1999; Szabo et al., 2002; Fleisch, 2003). The biological activity of bis­phospho­nates is dependent on the structure (Graham & Russell, 2007), lipophilicity (Zhang et al., 2009) and bone-binding affinity (Nancollas et al., 2006) of the compounds. Organic di­phospho­nic acids are potentially very powerful chelating agents used in metal extraction and have been tested by the pharmaceutical industry for use as efficient drugs to prevent calcification and to inhibit bone resorption (Tromelin et al., 1986; Matczak-Jon & Videnova-Adrabinska, 2005). However, it is still not clearly understood why small structural modifications of bis­phospho­nates may lead to extensive alterations in their physicochemical, biological and toxicological characteristics (Matczak-Jon & Videnova-Adrabinska, 2005). As a consequence, determination of the structure of bis­phospho­nates is very important to understand the influence of structural modifications on their complex-forming abilities and physiological activities, and for deriving structure–property relationships in general.

The crystal structures of tetra­hydro­furanyl-2,2-bis­phospho­nic acid disodium salt (Maltezou et al., 2010) and (1-ammonio­ethane-1,1-diyl)bis­(hydrogenphospho­nato)]di­aqua­chloridodisodium (Rukiah & Assaad, 2012) have been reported previously. In this paper, the crystal structure of the title compound, (I), is reported. This compound crystallizes as a fine white powder and, since no single crystal of sufficient size and quality was obtained, structure determination by powder X-ray diffraction was undertaken. We used laboratory powder X-ray diffraction data to solve and refine the crystal structure of (I).

This is a 12-atom (non-H) problem which requires careful measurement and inter­pretation of the in-house data in order to optimize the quality of the results. Compound (I) crystallizes in the triclinic system in a centrosymmetric space group (P1), with one molecule in the asymmetric unit. The asymmetric unit (Fig. 1) contains one (1-aza­niumyl­ethane-1,1-diyl)bis­(hydrogen phospho­nate) anion and one Na⁺ cation. The bis­phospho­nate anion in (I) has an overall -1 charge, and thus two of the phospho­nate O atoms are deprotonated (P—O^-), two have H atoms attached (P—OH) and two form double bonds with P (P═O). Two of the four phospho­nate H atoms are used in the protonation, one for the amino group and the other for the Na⁺ cation. [Remove?]

The bond lengths and angles in (I) are in the normal ranges (Allen et al., 1987). Both P atoms exhibit a distorted tetra­hedral geometry, with average P—OH(protonated) = 1.592 Å, average P—O(deprotonated) = 1.554 Å and average P═O = 1.490 Å (Table 1). Although the P—OH bonds can be located very easily by inspection of the bond lengths, the P—O^- and P═O bonds cannot be distinguished because of the charge delocalization over the O^-—P═O groups. The Na—O bond lengths range from 2.202 (9) to 2.680 (13) Å (average 2.462 Å), with Na1—O2(x, y + 1, z) being the longest. The central Na⁺ cations exhibit a distorted o­cta­hedral coordination geometry involving six bis­phospho­nate O atoms (two oxide, two hy­droxy and two double-bond O atoms). Two neighbouring sodium-centred o­cta­hedra form an edge-sharing environment, connected to each other by the bis­phospho­nate anions to form two-dimensional infinite sheets parallel to the (001) plane. The two-dimensional networks are stacked on top of each other along the c axis. The layers are further connected by extensive N—H···O and O—H···O hydrogen bonding (Table 2); the strongest is O1—H1···O3(-x, -y, -z + 1), which links the layers into a three-dimensional network (Fig. 2 and Table 2).

S2. Synthesis and crystallization

For the syntheses of (I), a mixture of aceto­nitrile (150 ml) and phospho­rus [phospho­ric?] acid (16.8 g, 0.2 mol) in acetic acid (10 g, 0.167 mol) was heated at 328–338 K and phospho­ryl trichloride (POCl₃; 51.7 g, 0.334 mol) was added slowly with stirring. After completion of the addition, the reaction mixture was kept for 24 h at 343–348 K. The reaction mixture was then cooled to 333–338 K and water (150 ml) was added slowly at the same temperature. The temperature was increased to 363–373 K and maintained for 4–6 h. The solid product which formed was separated by filtration and washed with water and finally with methanol. Sodium hydroxide (1 N, 15 ml) was added to this solid (200 mg) and the pH was adjusted to 6–7. The mixture was stirred at room temperature for 18 h. The resulting solution was freeze-dried and the crude product was further purified by recrystallization from absolute ethanol and water [Solvent ratio?] at 273 K to produce the product, (I) (white powder; m.p. 549–553 K) in 77% yield. Spectroscopic analysis: ¹H NMR (D₂O, δ, p.p.m.): 1.60 (t, 3H, CH₃, J = 12.00 Hz); ¹³C{¹H} NMR (D₂O, δ, p.p.m.): 20.45 (1C, CH₃), 56.84 (1C, C—CH₃); ³¹P{¹H} NMR (D₂O, δ, p.p.m.): 13.73 (2P, P—OH); IR (KBr, ν, cm^-1): 3450 (NH₂), 3419 (OH), 1634.7 (O═P—O—H). Analytical data for (I), found: C 11.51, H 4.32, N 6.30%; calculated: C 10.58, H 3.55, N 6.17%.

S3. Refinement

For pattern indexing, the extraction of the peak positions was carried out with the program WinPLOTR (Roisnel & Rodriguez-Carvajal, 2001). Pattern indexing was performed with the program DICVOL4.0 (Boultif & Louër, 2004). The first 20 lines of the powder pattern were completely indexed on the basis of a primitive triclinic cell. The absolute error on each observed line was fixed at 0.02° (2θ). The figures of merit are sufficiently good to support the obtained indexing results [M(20) = 41.0 and F(20) = 72.8(0.0081, 34)]. The whole powder diffraction pattern from 8 to 85° (2θ) was subsequently refined with cell and resolution constraints (Le Bail et al., 1988) in space group P1, using the `profile matching' option of the program FULLPROF (Rodriguez-Carvajal, 2001). The number of molecules per unit cell was estimated to be Z = 2. The structure was solved by direct methods using the program EXPO2009 (Altomare et al., 2009). The model found by this program was introduced into the program GSAS (Larson & Von Dreele, 2004) implemented in EXPGUI (Toby, 2001) for Rietveld refinement. The background was refined using a shifted Chebyshev polynomial with 20 coefficients. During the Rietveld refinement, the effect of asymmetry of low-order peaks was corrected using a pseudo-Voigt description of the peak shape (Thompson et al., 1987), which allows for angle-dependent asymmetry with axial divergence (Finger et al., 1994) and microstrain broadening as described by Stephens (1999). The two asymmetry parameters of this function, S/L and D/L, were both fixed at 0.0235 during the Rietveld refinement. Intensities were corrected from absorption effects with a µ.d value of 0.1. The preferred orientation was modelled with six coefficients using a spherical harmonics correction (Von Dreele, 1997) of intensities in the final refinement. The use of the preferred orientation correction leads to better molecular geometry with better agreement factors. Two C—CH₃ and C—NH₃ bond lengths were restrained to their normal values. The Rietveld refinement cycles were performed using a global isotropic atomic displacement parameter for each type of non-H atom. The hy­droxy H atoms were located in a difference map. The methyl and amino H atoms were positioned in their idealized geometries using a riding model, with C—H = 0.97 Å and N—H = 0.87 Å. The coordinates of these H atoms were not refined. The isotropic displacement parameters were set at 0.02 Ų. The final Rietveld agreement factors are R_p = 0.023, R_wp = 0.030, R_exp = 0.022, χ² = 1.904 and R_F² = 0.01638. The final Rietveld plot of the X-ray diffraction pattern is given in Fig. 3.

Related literature

For related literature, see: Abdou & Shaddy (2009); Allen et al. (1987); Altomare et al. (2009); Body et al. (1998); Boultif & Louër (2004); Finger et al. (1994); Fleisch (1998, 2003); Graham & Russell (2007); Larson & Von Dreele (2004); Le Bail, Duroy & Fourquet (1988); Maltezou et al. (2010); Matczak-Jon & Videnova-Adrabinska (2005); Nancollas et al. (2006); Rodriguez-Carvajal (2001); Roisnel & Rodriguez-Carvajal (2001); Rukiah & Assaad (2012); Russell & Rogers (1999); Stephens (1999); Szabo et al. (2002); Thompson et al. (1987); Toby (2001); Tromelin et al. (1986); Von Dreele (1997); Zhang (2009).

Computing details

Data collection: WinXPOW (Stoe & Cie, 1999); cell refinement: GSAS (Larson & Von Dreele, 2004); data reduction: WinXPOW (Stoe & Cie, 1999); program(s) used to solve structure: EXPO2009 (Altomare et al., 2009); program(s) used to refine structure: GSAS (Larson & Von Dreele, 2004); molecular graphics: ORTEP-3 (Farrugia, 2012); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The asymmetric unit of (I), showing the atom-labelling scheme. Isotropic displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A view of the crystal packing of (I), showing the formation of the three-dimensional network built from hydrogen bonds (dashed lines). [Where is the origin?]
	Fig. 3. The final Rietveld plot for (I). Observed data points are indicated by dots, and the best-fit profile (upper trace) and the difference pattern (lower trace) are solid lines. The vertical bars indicate the positions of the Bragg peaks.

Poly[[µ-(1-azaniumylethane-1,1-diyl)bis(hydrogen phosphonato)]sodium]

Crystal data

[Na(C2H8NO6P2)]	Z = 2
Mr = 227.02	F(000) = 232
Triclinic, P1	Dx = 1.96 Mg m^−3
Hall symbol: -P 1	Melting point: 551 K
a = 5.53651 (11) Å	Cu Kα1 radiation, λ = 1.5406 Å
b = 8.1058 (3) Å	µ = 5.76 mm^−1
c = 9.1108 (2) Å	T = 298 K
α = 98.086 (2)°	Particle morphology: Fine powder
β = 102.0847 (16)°	white
γ = 101.4987 (19)°	flat sheet, 8 × 8 mm
V = 384.62 (2) Å^3	Specimen preparation: Prepared at 298 K and 101.3 kPa

Data collection

Stoe STADI P diffractometer	Scan method: step
Radiation source: sealed X-ray tube	Absorption correction: for a cylinder mounted on the ϕ axis [GSAS absorption/surface roughness correction (Larson & Von Dreele, 2004): function number 4; flat plate in transmission mode, absorbtion correction term (µ.d) not refined]
Ge (111) monochromator	Tmin = 0.811, Tmax = 0.857
Specimen mounting: powder loaded between two Mylar foils	2θmin = 5.0°, 2θmax = 85°, 2θstep = 0.02°
Data collection mode: transmission

Refinement

Least-squares matrix: full	Profile function: pseudo-Voigt function of the peak shape for angle-dependent asymmetry with axial divergence
Rp = 0.023	112 parameters
Rwp = 0.030	2 restraints
Rexp = 0.022	3 constraints
R(F^2) = 0.01639	H-atom parameters not refined
χ^2 = 1.904	(Δ/σ)max = 0.02
4000 data points	Background function: shifted Chebyshev polynomial with 20 coefficients.
Excluded region(s): none	Preferred orientation correction: spherical harmonics correction

Special details

Experimental. The sample was ground lightly in a mortar, loaded between two Mylar foils and fixed in the sample holder with a mask of 8.0 mm internal diameter

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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

	x	y	z	Uiso*/Ueq
P1	−0.1518 (7)	−0.0122 (8)	0.2627 (4)	0.0059 (8)*
P2	−0.0944 (7)	0.3408 (7)	0.1498 (4)	0.0059 (8)*
Na1	−0.5425 (7)	0.6265 (9)	0.1563 (5)	0.0181 (15)*
O1	−0.3231 (14)	−0.1030 (15)	0.3623 (9)	0.0068 (11)*
O2	−0.2119 (14)	−0.1095 (15)	0.1071 (8)	0.0068 (11)*
O3	0.1283 (10)	0.0369 (14)	0.3564 (8)	0.0068 (11)*
O4	−0.2585 (12)	0.4757 (12)	0.1325 (7)	0.0068 (11)*
O5	−0.1653 (11)	0.2225 (14)	−0.0154 (7)	0.0068 (11)*
O6	0.1881 (11)	0.4144 (13)	0.2207 (8)	0.0068 (11)*
N1	−0.5181 (12)	0.1551 (15)	0.2009 (7)	0.0043 (17)*
C1	−0.2364 (14)	0.2020 (19)	0.2643 (10)	0.0043 (17)*
C2	−0.2002 (16)	0.3029 (17)	0.4283 (10)	0.0043 (17)*
H1	−0.23908	−0.08842	0.45130	0.0200*
H1N1	−0.59564	0.12310	0.26919	0.0200*
H2N1	−0.56649	0.24522	0.17275	0.0200*
H2A	−0.02088	0.35841	0.47085	0.0200*
H2B	−0.29612	0.39237	0.42348	0.0200*
H2C	−0.25879	0.22830	0.49336	0.0200*
H3N1	−0.55873	0.07302	0.12121	0.0200*
H5	−0.03482	0.20831	−0.03895	0.0200*

Geometric parameters (Å, º)

P1—O1	1.592 (11)	Na1—O4^iii	2.575 (8)
P1—O2	1.458 (9)	Na1—O5^iii	2.475 (10)
P1—O3	1.548 (8)	O1—H1	0.83
P1—C1	1.885 (15)	O5—H5	0.82
P2—O4	1.559 (10)	N1—C1	1.495 (11)
P2—O5	1.592 (8)	N1—H1N1	0.87
P2—O6	1.522 (8)	N1—H2N1	0.88
P2—C1	1.815 (13)	N1—H3N1	0.87
Na1—O4	2.202 (9)	C1—C2	1.552 (14)
Na1—O6^i	2.270 (11)	C2—H2A	0.97
Na1—O1^ii	2.575 (12)	C2—H2B	0.98
Na1—O2^ii	2.680 (13)	C2—H2C	0.96
O1—P1—O2	111.6 (6)	P1—O2—Na1^iv	95.0 (5)
O1—P1—O3	108.3 (5)	P2—O4—Na1	162.8 (5)
O1—P1—C1	103.3 (5)	P2—O4—Na1^iii	96.4 (4)
O2—P1—O3	118.5 (5)	Na1—O4—Na1^iii	91.8 (3)
O2—P1—C1	111.0 (6)	P2—O5—Na1^iii	99.5 (5)
O3—P1—C1	102.9 (6)	P2—O6—Na1^v	128.5 (5)
O4—P2—O5	104.7 (4)	Na1^iv—O1—H1	133
O4—P2—O6	115.3 (6)	P1—O1—H1	110
O4—P2—C1	104.9 (5)	P2—O5—H5	109
O5—P2—O6	115.8 (4)	Na1^iii—O5—H5	123
O5—P2—C1	103.6 (6)	C1—N1—H2N1	109
O6—P2—C1	111.3 (5)	C1—N1—H3N1	110
O4—Na1—O6^i	94.7 (4)	C1—N1—H1N1	111
O1^ii—Na1—O4	107.9 (3)	H2N1—N1—H3N1	109
O2^ii—Na1—O4	86.6 (3)	H1N1—N1—H3N1	110
O4—Na1—O4^iii	88.2 (3)	H1N1—N1—H2N1	109
O4—Na1—O5^iii	143.4 (3)	P1—C1—C2	112.8 (8)
O1^ii—Na1—O6^i	117.5 (3)	P1—C1—N1	103.5 (9)
O2^ii—Na1—O6^i	174.8 (3)	N1—C1—C2	103.9 (7)
O4^iii—Na1—O6^i	93.5 (3)	P2—C1—N1	108.3 (7)
O5^iii—Na1—O6^i	102.8 (3)	P2—C1—C2	110.2 (10)
O1^ii—Na1—O2^ii	57.3 (3)	P1—C1—P2	117.0 (5)
O1^ii—Na1—O4^iii	142.7 (4)	C1—C2—H2A	109
O1^ii—Na1—O5^iii	92.2 (4)	C1—C2—H2B	109
O2^ii—Na1—O4^iii	91.6 (3)	C1—C2—H2C	111
O2^ii—Na1—O5^iii	78.9 (3)	H2A—C2—H2B	108
O4^iii—Na1—O5^iii	59.2 (3)	H2A—C2—H2C	110
P1—O1—Na1^iv	95.8 (4)	H2B—C2—H2C	109
O2—P1—O1—Na1^iv	5.2 (6)	O5—P2—O6—Na1^v	72.8 (9)
O3—P1—O1—Na1^iv	−127.0 (5)	C1—P2—O6—Na1^v	−169.2 (6)
C1—P1—O1—Na1^iv	124.4 (4)	O4—P2—C1—P1	162.9 (5)
O1—P1—O2—Na1^iv	−5.0 (6)	O4—P2—C1—N1	46.6 (9)
O3—P1—O2—Na1^iv	121.8 (6)	O4—P2—C1—C2	−66.5 (7)
C1—P1—O2—Na1^iv	−119.5 (5)	O5—P2—C1—P1	53.3 (6)
O1—P1—C1—P2	−175.8 (5)	O5—P2—C1—N1	−63.0 (9)
O1—P1—C1—N1	−56.9 (6)	O5—P2—C1—C2	−176.1 (6)
O1—P1—C1—C2	54.8 (8)	O6—P2—C1—P1	−71.8 (7)
O2—P1—C1—P2	−56.2 (7)	O6—P2—C1—N1	171.9 (7)
O2—P1—C1—N1	62.8 (7)	O6—P2—C1—C2	58.8 (8)
O2—P1—C1—C2	174.5 (7)	O6^i—Na1—O4—Na1^iii	93.3 (3)
O3—P1—C1—P2	71.6 (6)	O1^ii—Na1—O4—Na1^iii	−145.7 (4)
O3—P1—C1—N1	−169.5 (5)	O2^ii—Na1—O4—Na1^iii	−91.7 (3)
O3—P1—C1—C2	−57.8 (8)	O4^iii—Na1—O4—Na1^iii	0.0 (3)
O5—P2—O4—Na1^iii	−3.2 (5)	O5^iii—Na1—O4—Na1^iii	−25.6 (8)
O6—P2—O4—Na1^iii	125.3 (4)	O4—Na1—O6^i—P2^i	−127.8 (6)
C1—P2—O4—Na1^iii	−111.9 (4)	O4—Na1—O1^ii—P1^ii	70.5 (5)
O4—P2—O5—Na1^iii	3.3 (5)	O4—Na1—O2^ii—P1^ii	−110.4 (5)
O6—P2—O5—Na1^iii	−124.9 (5)	O4—Na1—O4^iii—P2^iii	−164.8 (5)
C1—P2—O5—Na1^iii	113.0 (5)	O4—Na1—O4^iii—Na1^iii	0.0 (4)
O4—P2—O6—Na1^v	−49.9 (7)	O4—Na1—O5^iii—P2^iii	32.5 (9)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3^vi	0.83	1.69	2.499 (11)	165
N1—H1N1···O3^i	0.87	1.92	2.748 (11)	159
N1—H2N1···O6^i	0.88	2.18	2.911 (13)	141
N1—H3N1···O5^vii	0.87	2.51	3.235 (14)	142
O5—H5···O2^viii	0.82	1.88	2.679 (11)	163

Symmetry codes: (i) x−1, y, z; (vi) −x, −y, −z+1; (vii) −x−1, −y, −z; (viii) −x, −y, −z.