Silver diaquacobalt(II) catena-borodiphosphate(V) hydrate, (Ag0.79Co0.11)Co(H2O)2[BP2O8]·0.67H2O

Zouihri, H.; Saadi, M.; Jaber, B.; El Ammari, L.

doi:10.1107/S1600536811052020

inorganic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 68| Part 1| January 2012| Pages i3-i4

doi:10.1107/S1600536811052020

Open

access

Silver diaquacobalt(II) catena-borodiphosphate(V) hydrate, (Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈]·0.67H₂O

Hafid Zouihri,^a,^b Mohamed Saadi,^b Boujemaa Jaber ^a ^* and Lehcen El Ammari ^b

^aCentre National pour la Recherche Scientifique et Technique, Division UATRS, Angle Allal AlFassi et Avenue des FAR, Hay Ryad, BP 8027, Rabat, Morocco, and ^bLaboratoire de Chimie du Solide Appliquée, Faculté des Sciences, Université Mohammed V-Agdal, Avenue Ibn Batouta, BP 1014, Rabat, Morocco
^*Correspondence e-mail: b_jaber50@yahoo.com

(Received 14 November 2011; accepted 2 December 2011; online 7 December 2011)

The structure of the title compound, (Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈]·0.67H₂O is isotypic to that of its recently published counterparts AgMg(H₂O)₂[BP₂O₈]·H₂O and (Ag_0.57Ni_0.22)Ni(H₂O)₂[BP₂O₈]·0.67H₂O. It consists of infinite borophosphate helical ribbons [BP₂O₈]³⁻, built up from alternate BO₄ and PO₄ tetrahedra arranged around the 6₅ screw axes. The vertex-sharing BO₄ and PO₄ tetrahedra form a spiral ribbon of four-membred rings in which BO₄ and PO₄ groups alternate. The ribbons are connected through slightly distorted CoO₄(H₂O)₂ octahedra whose four O atoms belong to the phosphate groups. The resulting three-dimensional framework is characterized by hexagonal channels running along [001] in which the remaining water molecules are located. The main difference between the Mg-containing and the title structure lies in the filling ratio of Wyckoff positions 6a and 6b in the tunnels. The refinement of the occupancy rate of the site 6a shows that it is occupied by water at 67%, while the refinement of that of the site 6b shows that this site is partially occupied by 78.4% Ag and 10.8% Co, for a total of 82.2%. The structure is stabilized by O—H⋯O hydrogen bonds between water molecules and O atoms that are part of the helices.

Related literature

For the isotypic Mg and Ni analogues, see: Zouihri et al. (2011a ,b ); Menezes et al. (2008 ). For other similar borophosphates, see: Kniep et al. (1997 , 1998 ); Ewald et al. (2007 ); Lin et al. (2008 ). For ionic radii, see: Shannon (1976 ).

Experimental

Crystal data

(Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈]·0.67H₂O
M_r = 398.78
Hexagonal,
a = 9.4321 (11) Å
c = 15.750 (4) Å
V = 1213.5 (4) Å³
Z = 6
Mo Kα radiation
μ = 4.63 mm⁻¹
T = 296 K
0.16 × 0.12 × 0.10 mm

Data collection

Bruker APEXII CCD detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1999 ) T_min = 0.519, T_max = 0.630
7995 measured reflections
974 independent reflections
748 reflections with I > 2σ(I)
R_int = 0.096

Refinement

R[F² > 2σ(F²)] = 0.040
wR(F²) = 0.093
S = 1.07
974 reflections
77 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.83 e Å⁻³
Δρ_min = −0.54 e Å⁻³
Absolute structure: Flack (1983 ), 340 Friedel pairs
Flack parameter: −0.05 (5)

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O5—H5A⋯O4ⁱ	0.86	1.89	2.748 (6)	178
O5—H5B⋯O2	0.86	1.90	2.750 (6)	171
O6—H6A⋯O5ⁱⁱ	0.88	2.44	3.139 (11)	137
Symmetry codes: (i) $[-x+y, -x+1, z+{\script{1\over 3}}]$ ; (ii) .

Data collection: APEX2 (Bruker, 2005 ); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ) and DIAMOND (Brandenburg, 2006 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811052020/ru2019sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811052020/ru2019Isup2.hkl

checkCIF report

Comment top

A large group of borophosphates is known with a molar ratio of B:P = 1:2 and helical structure type, which consist of loop branched chain anions built from tetrahedral BO₄ and PO₄ units (Kniep et al., (1998); Menezes et al.,(2008) and Lin et al. (2008)).

The aim of this work is the synthesis and the crystal structure of a new borophosphate-hydrate (Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈],0.67(H₂O), which is isotypic to the analogue nickel and magnesium borophosphates (Ag_0.57Ni_0.22)Ni(H₂O)₂[BP₂O₈],0.67(H₂O); AgMg(H₂O)₂[BP₂O₈],H₂O recently published (Zouihri et al., 2011a, 2011b)) and to M^(I)M^(II)(H₂O)₂[BP₂O₈] H₂O (M^(I)=Li, Na, K, NH₄⁺; M^(II)= Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd) (Kniep et al., (1997) and Ewald et al., (2007)).

The anionic partial structure of the title compound contains one–dimensional infinite helices, [BP₂O₈]^3-, which are wound around 6₅ axis. It is built up from alternate borate (BO₄) and phosphate (PO₄) tetrahedra, forming a spiral ribbon. The Co²⁺ cations have a slightly distorted octahedral oxygen coordination by four oxygen atoms from the phosphate anion and by two from water molecules as shown in Fig.1. The ribbons are interconnected through CoO₄(H₂O)₂ octahedra. The resulting 3-D framework shows hexagonal tunnels running along c direction where water molecules are located (Fig.2).

The main difference between the structure of this compound and that of his counterpart AgMg(H₂O)₂[BP₂O₈],H₂O lies in the filling ratio of the Wyckoff positions 6a and 6 b in tunnels. Indeed, in this work, the refinement of the occupancy rate of the sites 6a and 6 b (space group P6₅22) shows that the first is occupied by water at 67% and the second is partially occupied by 78.4% of Ag and 10.8% of Co for a total of 82.2%. Note that in this case, the sum of the occupancie rate is restrained to fit the charge balance. While in the case of AgMg(H₂O)₂[BP₂O₈],H₂O structure these two sites are completely occupied by H₂O and Ag⁺ respectively.

It is interesting to compare the lattice parameters and volumes of title compound (Table 1) with some borophosphates of this family like AgMg(H₂O)₂[BP₂O₈],H₂O (a = 9.4577 (4) Å, c = 15.830 (2)Å and V = 1226.4 (2)Å₃) and (Ag_0.57Ni_0.22)Ni(H₂O)₂[BP₂O₈],0.67(H₂O) (a = 9.3848 (6) Å, c = 15.841 (2)Å and V = 1208.3 (2)Å₃). The ionic radii of Mg_II, Co_II, and Ni_II in the octahedral site are 0.72 Å, 0.74 Å and 0.69 Å, respectively (Shannon, 1976). The difference between these values is very small, therefore the filling rate of 6a and 6 b sites by (Ag_I/ M_II) and H₂O, respectively, leads to the variation of the lattice parameters and volumes of these compounds. Indeed the obtained values for the title compound are between these of the two precedents borophosphates as expected.

The structure is stabilized by O—H···O hydrogen bonds between water molecules and O atoms that are part of the helices (Table 2).

Related literature top

For the isotypic Mg analogue, see: Zouihri et al. (2011a,b); Menezes et al. (2008). For other similar borophosphates, see: Kniep et al. (1997, 1998); Ewald et al. (2007); Lin et al. (2008). For ionic radii, see: Shannon (1976).

Experimental top

The title borophosphate compound was hydrothermally synthesized at 453 °K for 7 days in a 25 ml Teflon-lined steel autoclave from the mixture of CoCO₃, H₃BO₃, H₃PO₄ (85%), AgNO₃ and 5 ml of distilled water in the molar ratio of 1:4:6:1:165. The reaction product was separated by filtration, washed with hot water and dried in air. The pink hexagonal bipyramid crystals obtained were up to 0.15 mm in length. Except for boron and hydrogen the presence of the elements were additionally confirmed by EDAX measurements. Indeed, the results of semi quantitative EDAX measurements are: Element, in At %: BK = 22.45; OK = 59.13; PK = 8.88; Ag L = 4.68, Co = 4.87 K. These values show a large excess of boron which is not surprising because the excess of boron comes from the synthesis of crystals.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top

Fig. 1. Partial plot of (Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈],0.67(H₂O) crystal structure showing polyhedra linkage. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) -y + 1, -x + 1, -z + 13/6; (ii) y - 1, -x + y, z + 1/6; (iii) y - 1, x, -z + 5/3; (iv) x, x-y + 1, -z + 11/6; (v) -x + y - 1, y, -z + 3/2; (vi) -x, -x + y, -z + 4/3; (vii) y, x + 1, -z + 5/3; (viii) x-y + 1, -y + 2, -z + 2.

Fig. 2. Projection view of the (Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈],0.67(H₂O) framework structure showing tunnel running along c direction where water molecules are located.

Silver diaquacobalt(II) catena-borodiphosphate(V) hydrate top

Crystal data top

(Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈]·0.67H₂O	D_x = 3.274 Mg m⁻³
M_r = 398.78	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P6₅22	Cell parameters from 974 reflections
Hall symbol: P 65 2 ( 0 0 1)	θ = 2.8–27.9°
a = 9.4321 (11) Å	µ = 4.63 mm⁻¹
c = 15.750 (4) Å	T = 296 K
V = 1213.5 (4) Å³	Prism, pink
Z = 6	0.16 × 0.12 × 0.10 mm
F(000) = 1155

Data collection top

Bruker APEXII CCD detector diffractometer	974 independent reflections
Radiation source: fine-focus sealed tube	748 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.096
ω and ϕ scans	θ_max = 27.9°, θ_min = 2.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 1999)	h = −12→11
T_min = 0.519, T_max = 0.630	k = −10→12
7995 measured reflections	l = −15→20

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.040	H-atom parameters constrained
wR(F²) = 0.093	w = 1/[σ²(F_o²) + (0.0409P)² + 1.3662P] where P = (F_o² + 2F_c²)/3
S = 1.07	(Δ/σ)_max < 0.001
974 reflections	Δρ_max = 0.83 e Å⁻³
77 parameters	Δρ_min = −0.54 e Å⁻³
1 restraint	Absolute structure: Flack (1983), 340 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.05 (5)

Crystal data top

(Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈]·0.67H₂O	Z = 6
M_r = 398.78	Mo Kα radiation
Hexagonal, P6₅22	µ = 4.63 mm⁻¹
a = 9.4321 (11) Å	T = 296 K
c = 15.750 (4) Å	0.16 × 0.12 × 0.10 mm
V = 1213.5 (4) Å³

Data collection top

Bruker APEXII CCD detector diffractometer	974 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1999)	748 reflections with I > 2σ(I)
T_min = 0.519, T_max = 0.630	R_int = 0.096
7995 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.040	H-atom parameters constrained
wR(F²) = 0.093	Δρ_max = 0.83 e Å⁻³
S = 1.07	Δρ_min = −0.54 e Å⁻³
974 reflections	Absolute structure: Flack (1983), 340 Friedel pairs
77 parameters	Absolute structure parameter: −0.05 (5)
1 restraint

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Ag1	0.18406 (7)	0.81594 (7)	1.0833	0.0491 (4)	0.784 (3)
Co1	0.18406 (7)	0.81594 (7)	1.0833	0.0491 (4)	0.1082 (16)
Co2	0.10332 (14)	0.55166 (7)	0.9167	0.0195 (3)
P	0.16844 (18)	0.77958 (17)	0.75218 (11)	0.0176 (3)
B	−0.1524 (6)	0.6952 (12)	0.7500	0.019 (2)
O1	0.1357 (6)	0.6203 (5)	0.7906 (2)	0.0224 (11)
O2	0.3146 (5)	0.9298 (5)	0.7861 (2)	0.0214 (10)
O3	0.0203 (5)	0.8048 (5)	0.7667 (3)	0.0195 (10)
O4	0.1833 (5)	0.7642 (5)	0.6541 (2)	0.0184 (9)
O5	0.2914 (5)	0.8033 (5)	0.9461 (3)	0.0263 (11)
H5A	0.3808	0.8058	0.9599	0.039*
H5B	0.3104	0.8472	0.8965	0.039*
O6	0.1183 (13)	1.0000	1.0000	0.099 (6)	0.67
H6A	0.2180	1.0790	0.9885	0.148*	0.67

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ag1	0.0534 (6)	0.0534 (6)	0.0438 (7)	0.0292 (6)	−0.0038 (5)	−0.0038 (5)
Co1	0.0534 (6)	0.0534 (6)	0.0438 (7)	0.0292 (6)	−0.0038 (5)	−0.0038 (5)
Co2	0.0187 (6)	0.0184 (5)	0.0214 (5)	0.0093 (3)	0.000	0.0008 (5)
P	0.0170 (8)	0.0188 (8)	0.0170 (7)	0.0090 (6)	0.0001 (7)	0.0000 (7)
B	0.021 (4)	0.022 (5)	0.014 (4)	0.011 (3)	0.004 (4)	0.000
O1	0.028 (3)	0.022 (2)	0.018 (2)	0.012 (2)	0.0026 (18)	0.0037 (17)
O2	0.017 (2)	0.020 (2)	0.022 (2)	0.006 (2)	−0.0012 (17)	0.0000 (18)
O3	0.014 (2)	0.016 (2)	0.027 (2)	0.0063 (18)	−0.0020 (17)	−0.0056 (18)
O4	0.019 (2)	0.018 (2)	0.019 (2)	0.0094 (19)	−0.0011 (16)	0.0008 (16)
O5	0.022 (2)	0.026 (3)	0.027 (2)	0.009 (2)	−0.0065 (18)	0.0060 (19)
O6	0.032 (6)	0.075 (11)	0.204 (17)	0.038 (6)	−0.043 (6)	−0.085 (12)

Geometric parameters (Å, º) top

Ag1—O5ⁱ	2.414 (4)	P—O3	1.547 (4)
Ag1—O5	2.414 (4)	P—O4	1.564 (4)
Ag1—O6ⁱ	2.489 (8)	B—O3^v	1.452 (7)
Ag1—O6	2.490 (8)	B—O3	1.452 (7)
Co2—O1	2.063 (4)	B—O4ⁱⁱⁱ	1.475 (7)
Co2—O1ⁱⁱ	2.063 (4)	B—O4^vi	1.475 (7)
Co2—O2ⁱⁱⁱ	2.084 (4)	O2—Co2^vii	2.084 (4)
Co2—O2^iv	2.084 (4)	O4—B^vi	1.475 (7)
Co2—O5	2.188 (4)	O5—H5A	0.8601
Co2—O5ⁱⁱ	2.188 (4)	O5—H5B	0.8600
P—O2	1.497 (4)	O6—Ag1^viii	2.490 (8)
P—O1	1.502 (4)	O6—H6A	0.8785

O5ⁱ—Ag1—O5	132.1 (2)	O1—P—O3	110.2 (3)
O5ⁱ—Ag1—O6ⁱ	79.6 (2)	O2—P—O4	111.0 (2)
O5—Ag1—O6ⁱ	147.77 (18)	O1—P—O4	106.7 (2)
O5ⁱ—Ag1—O6	147.77 (18)	O3—P—O4	106.8 (2)
O5—Ag1—O6	79.6 (2)	O3^v—B—O3	103.8 (7)
O6ⁱ—Ag1—O6	69.9 (4)	O3^v—B—O4ⁱⁱⁱ	113.5 (2)
O1—Co2—O1ⁱⁱ	165.3 (3)	O3—B—O4ⁱⁱⁱ	112.5 (2)
O1—Co2—O2ⁱⁱⁱ	100.77 (16)	O3^v—B—O4^vi	112.5 (2)
O1ⁱⁱ—Co2—O2ⁱⁱⁱ	89.30 (16)	O3—B—O4^vi	113.5 (2)
O1—Co2—O2^iv	89.30 (16)	O4ⁱⁱⁱ—B—O4^vi	101.5 (7)
O1ⁱⁱ—Co2—O2^iv	100.77 (17)	P—O1—Co2	128.7 (3)
O2ⁱⁱⁱ—Co2—O2^iv	94.3 (3)	P—O2—Co2^vii	139.9 (3)
O1—Co2—O5	87.21 (16)	B—O3—P	129.9 (4)
O1ⁱⁱ—Co2—O5	82.44 (16)	B^vi—O4—P	130.2 (4)
O2ⁱⁱⁱ—Co2—O5	87.56 (18)	Co2—O5—Ag1	96.38 (15)
O2^iv—Co2—O5	176.30 (15)	Co2—O5—H5A	109.6
O1—Co2—O5ⁱⁱ	82.44 (16)	Ag1—O5—H5A	101.7
O1ⁱⁱ—Co2—O5ⁱⁱ	87.21 (16)	Co2—O5—H5B	101.0
O2ⁱⁱⁱ—Co2—O5ⁱⁱ	176.31 (15)	Ag1—O5—H5B	141.3
O2^iv—Co2—O5ⁱⁱ	87.56 (18)	H5A—O5—H5B	104.5
O5—Co2—O5ⁱⁱ	90.8 (3)	Ag1—O6—Ag1^viii	106.6 (5)
O2—P—O1	115.7 (3)	Ag1—O6—H6A	99.5
O2—P—O3	106.1 (3)	Ag1^viii—O6—H6A	20.2

Symmetry codes: (i) −y+1, −x+1, −z+13/6; (ii) x, x−y+1, −z+11/6; (iii) y−1, −x+y, z+1/6; (iv) y−1, x, −z+5/3; (v) −x+y−1, y, −z+3/2; (vi) −x, −x+y, −z+4/3; (vii) y, x+1, −z+5/3; (viii) x−y+1, −y+2, −z+2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5A···O4^ix	0.86	1.89	2.748 (6)	178
O5—H5B···O2	0.86	1.90	2.750 (6)	171
O6—H6A···O5^viii	0.88	2.44	3.139 (11)	137

Symmetry codes: (viii) x−y+1, −y+2, −z+2; (ix) −x+y, −x+1, z+1/3.

Experimental details

Crystal data
Chemical formula	(Ag_0.79Co_0.11)Co(H₂O)₂[BP₂O₈]·0.67H₂O
M_r	398.78
Crystal system, space group	Hexagonal, P6₅22
Temperature (K)	296
a, c (Å)	9.4321 (11), 15.750 (4)
V (Å³)	1213.5 (4)
Z	6
Radiation type	Mo Kα
µ (mm⁻¹)	4.63
Crystal size (mm)	0.16 × 0.12 × 0.10

Data collection
Diffractometer	Bruker APEXII CCD detector diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1999)
T_min, T_max	0.519, 0.630
No. of measured, independent and observed [I > 2σ(I)] reflections	7995, 974, 748
R_int	0.096
(sin θ/λ)_max (Å⁻¹)	0.658

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.040, 0.093, 1.07
No. of reflections	974
No. of parameters	77
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.83, −0.54
Absolute structure	Flack (1983), 340 Friedel pairs
Absolute structure parameter	−0.05 (5)

Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 2006), WinGX (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5A···O4ⁱ	0.86	1.89	2.748 (6)	178.1
O5—H5B···O2	0.86	1.90	2.750 (6)	170.6
O6—H6A···O5ⁱⁱ	0.88	2.44	3.139 (11)	136.9

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

Acknowledgements

The authors thank the Unit of Support for Technical and Scientific Research (UATRS, CNRST) for the X-ray measurements.

References

Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Bruker (2005). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Ewald, B., Huang, Y.-X. & Kniep, R. (2007). Z. Anorg. Allg. Chem. 633, 1517–1540. Web of Science CrossRef CAS Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Kniep, R., Engelhardt, H. & Hauf, C. (1998). Chem. Mater. 10, 2930–2934. Web of Science CrossRef CAS Google Scholar
Kniep, R., Will, H. G., Boy, I. & Rohr, C. (1997). Angew. Chem. Int. Ed. Engl. 36, 1013–1014. CrossRef CAS Web of Science Google Scholar
Lin, J.-R., Huang, Y.-X., Wu, Y.-H. & Zhou, Y. (2008). Acta Cryst. E64, i39–i40. Web of Science CrossRef IUCr Journals Google Scholar
Menezes, P. W., Hoffmann, S., Prots, Y. & Kniep, R. (2008). Z. Kristallogr. 223, 333–334. CAS Google Scholar
Shannon, R. D. (1976). Acta Cryst. A32, 751–767. CrossRef CAS IUCr Journals Web of Science Google Scholar
Sheldrick, G. M. (1999). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Zouihri, H., Saadi, M., Jaber, B. & El Ammari, L. (2011a). Acta Cryst. E67, i44. Web of Science CrossRef IUCr Journals Google Scholar
Zouihri, H., Saadi, M., Jaber, B. & El Ammari, L. (2011b). Acta Cryst. E67, i39. Web of Science CrossRef IUCr Journals Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.