AgCo₃PO₄(HPO₄)₂

The structure of the hydro­thermally synthesized compound AgCo₃PO₄(HPO₄)₂, silver tricobalt phosphate bis­(hydrogen phosphate), consists of edge-sharing CoO₆ chains linked together by the phosphate groups and hydrogen bonds. The three-dimensional framework delimits two types of tunnels which accommodate Ag⁺ cations and OH groups. The title compound is isostructural with the compounds AM₃H₂(XO₄)₃ (A = Na or Ag, M = Co or Mn, and X = P or As) of the alluaudite structure type.

S1. Comment

The A—Co—X—O systems (A is a monovalent cation and X is P or As) have been investigated as part of a search for new materials which can exhibit interesting properties in relation to their structures (magnetism, ion exchange, ionic conductivity, etc.) In recent studies of the Na—Co—P—O system, we described the structure of Na₂Co(H₂PO₄)₄·4H₂O synthesized at room temperature (Guesmi et al., 2000). In the present study, we have investigated the Ag—Co—P—O system by the hydrothermal method and we obtained the title compound, the structure of which is presented here.

AgCo₃PO₄(HPO₄)₂ crystallizes in the monoclinic space group C2/c and is isostructural with the AM₃H₂(XO₄)₃-type compounds (A is Na or Ag, M is a metal and X is P or As) of the alluaudite structure type (Keller et al., 1981; Lii & Shih, 1994; Leroux et al., 1995). The P and Co atoms are surrounded by four and six O atoms, respectively. The mean distances are Co1—O 2.108, Co2—O 2.158, P1—O 1.551 and P2—O 1.552 Å, and these are in the same range as in the isostructural cobalt compounds; the longer distances, P1—O and Co2—O, involve the O atom of the OH group. The bond valence sums of the Ag, Co and P atoms are in good agreement with their oxidation states (Brese & O'Keeffe, 1985).

The structure consists of infinite chains of edge-sharing CoO₆ octahedra running along [101] and having a Co1—Co1—Co2 period. These chains are linked together by the phosphate groups to form polyhedral sheets parallel to the (101) plane (Fig. 1). Each P2O₄ tetrahedron shares its four vertices with two chains of the same sheet. Adjacent sheets are interconnected by the tricoordinate O5 vertex common to two Co1O₆ octahedra and the HP1O₄ tetrahedron.

The three-dimensional framework delimits two types of hexagonal tunnels running along the c direction, at 0,0,z and 1/2,0,z (Fig. 2). The OH groups, pointing into one type of tunnel, are involved in strong hydrogen bonds (Brown, 1976). Square plane coordinated Ag⁺ cations are located in the second type of tunnel. The same coordination for this cation is found in the homologous arsenates (Keller et al., 1981).

S2. Experimental

Single crystals of AgCo₃PO₄(HPO₄)₂ were prepared hydrothermally from an aqueous solution of AgNO₃ (Fluka, 99%), Co(NO₃)₂·6H₂O (Fluka, 99%) and H₃PO₄ (Prolabo, 85%, density 1.70 Mg m^-3), with the atomic ratio Ag:Co:P = 2:1:2. The mixture was filled in a glass tube to about 25% in volume. The tube was sealed and heated to 573 K for 3 d. Normal cooling to room temperature produced pink parallelepiped crystals of AgCo₃PO₄(HPO₄)₂.

S3. Refinement

The position of the H atom was obtained by difference techniques and the O6—H bond length was restrained to 0.80 Å by the DFIX option in SHELXL97 (Sheldrick, 1997). BUT s.u. given in Table 2 - please clarify.

Computing details

Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell refinement: CAD-4 EXPRESS; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of a sheet of the anionic framework of AgCo3PO4(HPO4)2 with 50% probability displacement ellipsoids.
	Fig. 2. A projection of the structure of AgCo3PO4(HPO4)2 along [001].

Silver tricobalt phosphate bis(hydrogen phosphate)

Crystal data

AgCo3PO4(HPO4)2	F(000) = 1084
Mr = 571.59	Dx = 4.320 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71069 Å
a = 12.035 (2) Å	Cell parameters from 25 reflections
b = 12.235 (2) Å	θ = 10.8–13.8°
c = 6.541 (2) Å	µ = 8.38 mm^−1
β = 114.14 (2)°	T = 293 K
V = 878.9 (3) Å^3	Parallelepiped, pink
Z = 4	0.43 × 0.18 × 0.14 mm

Data collection

Enraf-Nonius CAD4 diffractometer	932 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.013
Graphite monochromator	θmax = 27.0°, θmin = 2.5°
ω/2θ scans	h = −14→15
Absorption correction: ψ-scan (North et al., 1968)	k = −15→0
Tmin = 0.178, Tmax = 0.309	l = −8→0
1048 measured reflections	2 standard reflections every 120 min
961 independent reflections	intensity decay: 0.4%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.025	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.068	w = 1/[σ^2(Fo^2) + (0.0351P)^2 + 5.6691P] where P = (Fo^2 + 2Fc^2)/3
S = 1.22	(Δ/σ)max < 0.001
961 reflections	Δρmax = 0.97 e Å^−3
92 parameters	Δρmin = −1.46 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0184 (7)

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 (Ų)

	x	y	z	Uiso*/Ueq
Ag	0.0000	0.47148 (4)	0.2500	0.02258 (19)
Co1	0.29015 (4)	0.16196 (4)	0.37801 (8)	0.00841 (18)
Co2	0.5000	0.27873 (5)	0.2500	0.0094 (2)
P1	0.22255 (8)	0.38696 (7)	0.11416 (14)	0.0072 (2)
P2	0.0000	0.18372 (10)	0.2500	0.0073 (3)
O1	0.1068 (2)	0.1078 (2)	0.2663 (4)	0.0108 (5)
O2	0.0350 (2)	0.2557 (2)	0.4620 (4)	0.0092 (5)
O3	0.3443 (2)	0.1719 (2)	0.1121 (4)	0.0093 (5)
O4	0.2169 (2)	0.31838 (19)	0.3066 (4)	0.0090 (5)
O5	0.1628 (2)	0.4994 (2)	0.1069 (4)	0.0111 (5)
O6	0.3605 (2)	0.4057 (2)	0.1588 (4)	0.0105 (5)
H	0.384 (6)	0.467 (2)	0.193 (12)	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag	0.0098 (2)	0.0393 (3)	0.0152 (3)	0.000	0.00155 (18)	0.000
Co1	0.0084 (3)	0.0060 (3)	0.0109 (3)	0.00012 (16)	0.0040 (2)	0.00024 (16)
Co2	0.0086 (3)	0.0086 (3)	0.0109 (3)	0.000	0.0040 (3)	0.000
P1	0.0076 (4)	0.0046 (4)	0.0088 (4)	−0.0001 (3)	0.0027 (3)	−0.0003 (3)
P2	0.0057 (5)	0.0058 (5)	0.0086 (6)	0.000	0.0011 (4)	0.000
O1	0.0081 (11)	0.0069 (11)	0.0171 (13)	0.0008 (9)	0.0048 (10)	−0.0009 (9)
O2	0.0072 (11)	0.0098 (11)	0.0092 (11)	−0.0010 (9)	0.0020 (9)	−0.0010 (9)
O3	0.0092 (11)	0.0093 (11)	0.0083 (11)	−0.0014 (9)	0.0025 (9)	−0.0006 (8)
O4	0.0100 (11)	0.0076 (11)	0.0097 (11)	0.0002 (9)	0.0045 (9)	0.0006 (9)
O5	0.0100 (11)	0.0057 (10)	0.0168 (13)	0.0012 (9)	0.0045 (10)	0.0005 (9)
O6	0.0078 (11)	0.0067 (11)	0.0160 (12)	−0.0015 (9)	0.0039 (9)	−0.0008 (9)

Geometric parameters (Å, º)

Ag—O5^i	2.382 (3)	Co2—O3	2.156 (2)
Ag—O5^ii	2.382 (3)	Co2—O3^vii	2.156 (2)
Ag—O5	2.516 (3)	Co2—O6^vii	2.184 (3)
Ag—O5^iii	2.516 (3)	Co2—O6	2.184 (3)
Co1—O5^iv	2.059 (3)	P1—O4	1.537 (2)
Co1—O4	2.079 (2)	P1—O3^viii	1.543 (3)
Co1—O3	2.096 (3)	P1—O5	1.544 (3)
Co1—O4^v	2.113 (2)	P1—O6	1.581 (3)
Co1—O1	2.126 (2)	P2—O2	1.549 (3)
Co1—O2^v	2.176 (2)	P2—O2^iii	1.549 (3)
Co2—O2^v	2.134 (2)	P2—O1^iii	1.554 (2)
Co2—O2^vi	2.134 (2)	P2—O1	1.554 (2)
O5^i—Ag—O5^ii	162.80 (12)	O2^v—Co2—O3^vii	87.85 (9)
O5^i—Ag—O5	83.73 (8)	O2^vi—Co2—O3^vii	78.36 (9)
O5^ii—Ag—O5	93.94 (8)	O3—Co2—O3^vii	105.36 (13)
O5^i—Ag—O5^iii	93.94 (8)	O2^v—Co2—O6^vii	107.85 (10)
O5^ii—Ag—O5^iii	83.73 (8)	O2^vi—Co2—O6^vii	88.53 (10)
O5—Ag—O5^iii	164.39 (12)	O3—Co2—O6^vii	170.02 (9)
O5^iv—Co1—O4	169.42 (10)	O3^vii—Co2—O6^vii	82.99 (9)
O5^iv—Co1—O3	85.57 (10)	O2^v—Co2—O6	88.53 (10)
O4—Co1—O3	90.43 (10)	O2^vi—Co2—O6	107.85 (10)
O5^iv—Co1—O4^v	100.56 (10)	O3—Co2—O6	82.99 (9)
O4—Co1—O4^v	86.10 (10)	O3^vii—Co2—O6	170.02 (9)
O3—Co1—O4^v	162.56 (10)	O6^vii—Co2—O6	89.27 (13)
O5^iv—Co1—O1	86.66 (10)	O4—P1—O3^viii	110.50 (14)
O4—Co1—O1	85.68 (9)	O4—P1—O5	109.60 (14)
O3—Co1—O1	111.36 (10)	O3^viii—P1—O5	109.41 (14)
O4^v—Co1—O1	85.45 (10)	O4—P1—O6	108.84 (14)
O5^iv—Co1—O2^v	103.38 (10)	O3^viii—P1—O6	109.97 (14)
O4—Co1—O2^v	85.38 (10)	O5—P1—O6	108.49 (14)
O3—Co1—O2^v	78.72 (10)	O2—P2—O2^iii	110.7 (2)
O4^v—Co1—O2^v	83.96 (9)	O2—P2—O1^iii	108.41 (13)
O1—Co1—O2^v	166.57 (10)	O2^iii—P2—O1^iii	111.33 (13)
O2^v—Co2—O2^vi	157.24 (14)	O2—P2—O1	111.33 (13)
O2^v—Co2—O3	78.36 (9)	O2^iii—P2—O1	108.41 (13)
O2^vi—Co2—O3	87.85 (9)	O1^iii—P2—O1	106.59 (19)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O6—H···O1^ix	0.80 (3)	1.74 (3)	2.520 (3)	164 (8)

Symmetry code: (ix) −x+1/2, y+1/2, −z+1/2.