Hexaaquacobalt(II) bis(hypophosphite) and hexaaquacobalt(II)/nickel(II) bis(hypophosphite)

The title compounds, hexa­aqua­cobalt(II) bis­(hypophosphite), [Co(H₂O)₆](H₂­PO₂)₂, and hexa­aqua­cobalt(II)/nickel(II) bis(hypophosphite), [Co_0.5Ni_0.5(H₂O)₆](H₂PO₂)₂, are shown to adopt the same structure as hexa­aqua­magnesium(II) bis­(hypophosphite). The packing of the Co(Ni) and P atoms is the same as in the structure of CaF₂. The Co^II(Ni^II) atoms have a pseudo-face-centred cubic cell, with a = b ∼ 10.3 Å, and the P atoms occupy the tetrahedral cavities. The central metal cation has a slightly distorted octahedral coordination sphere. The geometry of the hypophosphite anion in the structure is very close to ideal, with point symmetry mm2. Each O atom of the hypophosphite anion is hydrogen bonded to three water mol­ecules from different cation complexes, and each H atom of the hypophosphite anion is surrounded by three water mol­ecules from further different cation complexes.

S1. Comment

Investigations of hexahydrate bivalent metal hypophosphites have been reported by Ferrari & Colla (1937), Pedrazuela et al. (1953) and Galigné & Dumas (1973). Here, we report the results of the single-crystal X-ray diffraction analysis of hexaaquacobalt(II) bis(hypophosphite), [Co(H₂O)₆](H₂PO₂)₂, (I), and hexaaquacobalt(II)/nickel(II) (0.5/0.5) bis(hypophosphite), [Co_0.5Ni_0.5(H₂O)₆](H₂PO₂)₂, (II), which are very similar to the structure of hexaaquamagnesium(II) bis(hypophosphite) (Galigné & Dumas, 1973). The crystals of (II) are a solid solution of the Co^II and Ni^II hypophosphites. The calculated powder pattern of (II) is in good agreement with the experimental one. \sch

The packing of the Co^II(Ni^II) and P atoms (not the hypophosphite anion) is the same as the structure of CaF₂. The Co^II(Ni^II) atoms have a pseudo-face-centred cubic cell with a = b ~10.3 Å, and the P atoms occupy the tetrahedral cavities. The powder pattern for (I) was reported earlier by Ferrari & Colla (1937), and it was indexed as a cubic system with a cell parameter of 10.22 Å. Some differences between the work of Ferrari & Colla and our studies are in evidence, in that reflections at high angles could be indexed as a Cu Kα₁ - Cu Kα₂ relation; indeed, this is the complex result of an unclear ratio for c = 2a, because of an incomplete range for the powder data (only from d = 3.090 Å) and a real Cu Kα₁ - Cu Kα₂ relation. The experimental powder patterns are in good agreement with the known powder pattern at high angles, but the reflections responsible for the c parameter at small angles were missed in the conditions used by Ferrari & Colla (1937).

The coordination number of six for bivalent metals (Mg, Co, Ni) is achieved by water molecules; the hypophosphite anion does not coordinate to the metal cation. The metal cation has a slightly distorted octahedral coordination sphere. The average M—O distances are 2.05 (1) Å in magnesium(II) bis(hypophosphite) (Galigné & Dumas, 1973), 2.074 (3) Å in (I) and 2.055 (2) Å in (II). There are two types of orientation for the water molecules relative to the oppositely coordinated water molecule. The torsion angles between the two planes, consisting of one O atom and two H atoms of oppositely coordinated water molecules, are: type 1 [two pairs, O2W and O2Wⁱ with their opposite symmetry equivalents; symmetry code: (i) ?] 65.1 (1)° in magnesium(II) bis(hypophosphite) (Galigné & Dumas, 1973), 78.0 (1)° in (I) and 69.8 (1)° in (II); type 2 (one pair, O1W with its opposite symmetry equivalent) 3.0 (1)° in magnesium(II) bis(hypophosphite) (Galigné & Dumas, 1973), 2.8 (1)° in (I) and 1.6 (1)° in (II) (Fig. 1).

The second coordination sphere of the metal atom consists of eight hypophosphite anions, which are hydrogen bonded to the water molecules coordinated to the [Co(H₂O)₆]²⁺ ([Ni(H₂O)₆]²⁺) cation (Fig. 1). This rigid construction is three-dimensional, like the structure of CaF₂.

The geometry of the hypophosphite anion in the structures of (I) and (II) is very close to the ideal, with point symmetry mm2 (Naumov et al., 2001, 2002). The geometric parameters for the anion (Tables 1 and 2) are comparable with earlier reported data, with P—O distances and O—P—O angles, respectively, of 1.507 (3) Å and 116.2 (3)° in [Mg(H₂O)₆](H₂PO₂)₂ (Galigné & Dumas, 1973), 1.527 (1) and 1.516 (1) Å, and 115.3 (3)° in Co(H₂PO₂)Cl(H₂O) (Marcos et al., 1991), and 1.541 (2) and 1.480 (2) Å, and 118.7 (3)° in Ni(H₂PO₂)Cl(H₂O) (Marcos et al., 1993).

Each O atom of the hypophosphite anion is hydrogen bonded to three water molecules from different cation complexes (Tables 1 and 2; thick dotted lines in Fig. 2). Each H atom of the hypophosphite anion is surrounded by three water molecules from further different cation complexes, and these H atoms are situated directly above the centres of the triangles formed by the O atom and two H atoms of the water molecules (thin dotted lines in Fig. 2). The distances between atom H1 of the hypophosphite and the O atoms [O2Wⁱ, O1Wⁱⁱ and O2Wⁱⁱⁱ; symmetry codes: (i) 1/4 - y, x - 1/4, 1/4 + z; (ii) 1/2 + x, -y, z; (iii) 1/2 + x, y, 1/2 - z] of the water molecules are 2.93 (2), 2.94 (2) and 2.95 (2) Å (average 2.94 Å) for (I), and 2.865 (16), 2.912 (17) and 2.850 (16) Å (average 2.88 Å) for (II). This environment can be found in all three structures of hexaaquamagnesium(II), -cobalt(II) and -cobalt(II)/nickel(II) bis(hypophosphite)s.

The English has been extensively rephrased in this section; do please check very carefully to make sure the sense has not been altered.

S2. Experimental

Compound (I) was synthesized by the slow evaporation of an aqueous solution of cobalt(II) hypophosphite, which was prepared by adding a solution of calcium hypophosphite, Ca(H₂PO₂)₂, to cobalt(II) sulfate, CoSO₄, in an equimolar ratio. The reaction mixture was filtered and crystals of (I) were grown at 293 K in air. Compound (II) was synthesized by mixing aqueous solutions of cobalt(II) and nickel(II) bis(hypophosphite)s in an equimolar ratio. Purple-green crystals of (II) were grown at 293 K in air Please clarify - light-green given below, and their chemical composition was determined by UV spectroscopy. The UV spectrum of the hexaaquacobalt(II) cation has no overlap with that for Ni (maximum absorption 317 and 288 nm, respectively). The quantities of each cation in the crystals were calculated using calibration solutions of the pure cobalt(II) and nickel(II) bis(hypophosphite)s. The actual ratio of metals in the crystals was found to be the same as that calculated based on the preparation experiment.

S3. Refinement

In both structures, the H atoms were located from a difference electron-density map. The positions of the H atoms were refined without any constraints.

Computing details

For both compounds, data collection: CD4CA0 (Enraf-Nonius, 1989); cell refinement: CD4CA0; data reduction: CADDAT (Enraf-Nonius, 1989); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The environment of the hexaaqua Co^II cation of (I), in relation to the hypophosphite anions; the environment of the Co^II/Ni^II (0.5/0.5) cation in (II) is equivalent. Is this added text correct? Displacement ellipsoids are plotted at the 50% probability level and H atoms are drawn as small spheres of arbitrary radii [symmetry codes: (i) 1/4 - y, 1/4 - x, 1/4 - z; (ii) x, -y, 1/2 - z; (iii) y - 1/4, x - 1/4, z - 1/4].

Fig. 2. The environment of the hypophosphite anion of (I), in relation to the hexaaqua Co^II cations, viewed along [001]; the corresponding diagram in relation to the Co^II/Ni^II (0.5/0.5) cations in (II) is equivalent. Is this added text correct? The thick dotted lines indicate the O—H···O—P hydrogen bonds, and the thin dotted lines indicate the OW···H—P contacts.

(I) hexaaquacobalt(II) bis(hypophosphite)

Crystal data

[Co(H2O)6](H2PO2)2	Dx = 1.809 Mg m^−3
Mr = 297.00	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I41/acd	Cell parameters from 24 reflections
Hall symbol: -I 4bd 2c	θ = 9.7–12.0°
a = 10.3406 (15) Å	µ = 1.89 mm^−1
c = 20.402 (3) Å	T = 293 K
V = 2181.6 (6) Å^3	Prism, purple
Z = 8	0.64 × 0.36 × 0.36 mm
F(000) = 1224

Data collection

Enraf-Nonius CAD-4 diffractometer	419 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.030
Graphite monochromator	θmax = 28.3°, θmin = 3.4°
2θ/θ scans	h = 0→13
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989)	k = 0→13
Tmin = 0.477, Tmax = 0.506	l = 0→27
1315 measured reflections	3 standard reflections every 60 min
686 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	All H-atom parameters refined
wR(F^2) = 0.093	w = 1/[σ^2(Fo^2) + (0.0536P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.92	(Δ/σ)max < 0.001
686 reflections	Δρmax = 0.51 e Å^−3
49 parameters	Δρmin = −0.41 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: 0.0004 (1)

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
Co1	0.0000	0.2500	0.1250	0.0307 (2)
P1	0.24094 (8)	0.0000	0.2500	0.0326 (3)
H1	0.317 (2)	−0.063 (2)	0.2823 (9)	0.043 (7)*
O1	0.16340 (15)	0.08764 (15)	0.29407 (6)	0.0358 (4)
O1W	0.0000	0.2500	0.22648 (12)	0.0518 (7)
H1W	0.045 (3)	0.208 (3)	0.2457 (13)	0.037 (6)*
O2W	0.0026 (2)	0.04922 (17)	0.12380 (13)	0.0552 (6)
H2W	0.043 (3)	0.016 (3)	0.1410 (11)	0.035 (9)*
H3W	−0.047 (3)	0.015 (3)	0.1044 (11)	0.054 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0301 (3)	0.0301 (3)	0.0318 (4)	−0.00244 (18)	0.000	0.000
P1	0.0265 (7)	0.0371 (8)	0.0342 (4)	0.000	0.000	−0.0085 (3)
O1	0.0350 (9)	0.0364 (9)	0.0360 (7)	−0.0004 (6)	0.0012 (6)	−0.0085 (7)
O1W	0.055 (3)	0.067 (3)	0.0326 (13)	0.0300 (13)	0.000	0.000
O2W	0.0658 (13)	0.0304 (9)	0.0694 (12)	−0.0049 (9)	−0.0427 (10)	0.0025 (18)

Geometric parameters (Å, º)

Co1—O1W	2.070 (3)	O1W—H1W	0.75 (2)
Co1—O2W	2.0765 (18)	O2W—H2W	0.64 (2)
P1—O1	1.5076 (13)	O2W—H3W	0.74 (3)
P1—H1	1.21 (2)
O1W—Co1—O2W	90.68 (7)	O2W^i—Co1—O2W^iii	178.65 (14)
O1W—Co1—O2W^i	89.32 (7)	O1^iv—P1—O1	115.74 (13)
O2W—Co1—O2W^i	88.50 (14)	H1^iv—P1—H1	99 (2)
O2W—Co1—O2W^ii	178.65 (14)	H1W^ii—O1W—H1W	117 (4)
O2W—Co1—O2W^iii	91.51 (14)	H2W—O2W—H3W	119 (3)

Symmetry codes: (i) −y+1/4, −x+1/4, −z+1/4; (ii) −x, −y+1/2, z; (iii) y−1/4, x+1/4, −z+1/4; (iv) x, −y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1W···O1	0.75 (2)	2.01 (2)	2.7524 (18)	177 (3)
O2W—H2W···O1^iv	0.64 (2)	2.11 (3)	2.752 (3)	174 (3)
O2W—H3W···O1^v	0.74 (3)	2.01 (3)	2.744 (3)	173 (3)

Symmetry codes: (iv) x, −y, −z+1/2; (v) y−1/4, x−1/4, z−1/4.

(II) hexaaquacobalt(II)/nickel(II) (0.5/0.5) bis(hypophosphite)

Crystal data

[Co0.5Ni0.5(H2O)6](H2PO2)2	Dx = 1.823 Mg m^−3
Mr = 296.89	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I41/acd	Cell parameters from 24 reflections
Hall symbol: -I 4bd 2c	θ = 9.7–12.1°
a = 10.3111 (13) Å	µ = 2.01 mm^−1
c = 20.346 (3) Å	T = 293 K
V = 2163.2 (5) Å^3	Octahedron, light green
Z = 8	0.65 × 0.63 × 0.57 mm
F(000) = 1228

Data collection

Enraf-Nonius CAD-4 diffractometer	407 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.016
Graphite monochromator	θmax = 27.5°, θmin = 3.4°
2θ/θ scans	h = 0→13
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989)	k = 0→13
Tmin = 0.288, Tmax = 0.317	l = 0→26
1187 measured reflections	3 standard reflections every 60 min
621 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.021	All H-atom parameters refined
wR(F^2) = 0.073	w = 1/[σ^2(Fo^2) + (0.0365P)^2 + 0.3503P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max < 0.001
621 reflections	Δρmax = 0.23 e Å^−3
49 parameters	Δρmin = −0.19 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: 0.0030 (3)

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	Occ. (<1)
Co1	0.0000	0.2500	0.1250	0.0293 (2)	0.50
Ni1	0.0000	0.2500	0.1250	0.0293 (2)	0.50
P1	0.24135 (6)	0.0000	0.2500	0.0319 (2)
O1	0.16368 (12)	0.08744 (12)	0.29460 (5)	0.0349 (4)
H1	0.3229 (16)	−0.0665 (17)	0.2876 (7)	0.023 (4)*
O1W	0.0000	0.2500	0.22614 (10)	0.0516 (6)
H1W	0.049 (3)	0.200 (2)	0.2487 (15)	0.071 (8)*
O2W	0.00205 (18)	0.05080 (15)	0.12382 (10)	0.0548 (5)
H2W	0.048 (2)	0.014 (2)	0.1409 (8)	0.033 (6)*
H3W	−0.052 (2)	0.015 (2)	0.1052 (9)	0.048 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0286 (2)	0.0286 (2)	0.0308 (3)	−0.00289 (14)	0.000	0.000
Ni1	0.0286 (2)	0.0286 (2)	0.0308 (3)	−0.00289 (14)	0.000	0.000
P1	0.0254 (5)	0.0357 (6)	0.0346 (4)	0.000	0.000	−0.0102 (2)
O1	0.0337 (7)	0.0355 (7)	0.0355 (6)	0.0003 (5)	0.0017 (5)	−0.0104 (5)
O1W	0.054 (2)	0.068 (2)	0.0326 (10)	0.0296 (11)	0.000	0.000
O2W	0.0648 (11)	0.0279 (8)	0.0718 (10)	−0.0053 (7)	−0.0441 (8)	0.0039 (12)

Geometric parameters (Å, º)

Co1—O1W	2.058 (2)	P1—H1	1.328 (15)
Co1—O2W	2.0542 (16)	O1W—H1W	0.86 (3)
Ni1—O1W	2.058 (2)	O2W—H2W	0.70 (2)
Ni1—O2W	2.0542 (16)	O2W—H3W	0.77 (2)
P1—O1	1.5092 (12)
O1W—Co1—O2W	90.67 (5)	O2W—Ni1—O2W^i	88.83 (10)
O1W—Co1—O2W^i	89.33 (5)	O2W—Ni1—O2W^ii	178.66 (11)
O2W—Co1—O2W^i	88.83 (10)	O2W—Ni1—O2W^iii	91.19 (10)
O2W—Co1—O2W^ii	178.66 (11)	O2W^i—Ni1—O2W^iii	178.66 (11)
O2W—Co1—O2W^iii	91.19 (10)	O1^iv—P1—O1	115.90 (11)
O2W^i—Co1—O2W^iii	178.66 (11)	H1^iv—P1—H1	101.4 (15)
O1W—Ni1—O2W	90.67 (5)	H1W^ii—O1W—H1W	115 (4)
O1W—Ni1—O2W^i	89.33 (5)	H2W—O2W—H3W	119 (3)

Symmetry codes: (i) −y+1/4, −x+1/4, −z+1/4; (ii) −x, −y+1/2, z; (iii) y−1/4, x+1/4, −z+1/4; (iv) x, −y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1W···O1	0.86 (3)	1.90 (3)	2.7565 (16)	177 (3)
O2W—H2W···O1^iv	0.70 (2)	2.06 (2)	2.750 (2)	170 (2)
O2W—H3W···O1^v	0.77 (2)	1.98 (2)	2.735 (2)	168 (2)

Symmetry codes: (iv) x, −y, −z+1/2; (v) y−1/4, x−1/4, z−1/4.