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In the title complex, [Co(CH3CN)2(H2O)4]Br2, the CoII atom lies on an inversion centre and is octahedrally coordinated by two trans acetonitrile molecules and four water molecules. Hydrogen bonding between the water molecules and lattice bromide ions yields a three-dimensional structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199012159/ta1257sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270199012159/ta1257Isup2.hkl
Contains datablock I

CCDC reference: 140921

Comment top

Despite there being numerous acetonitrile- and aqua-metal complexes reported in the literature, trans-bis(acetonitrile-N)tetraaquacobalt(II) bromide, (I), is the first reported structure of a metal complex where the ligands are exclusively coordinated water and acetonitrile molecules. The cobalt(II) atom lies on a centre of symmetry and is coordinated to two trans acetonitrile molecules and to four water molecules (Fig. 1). The metal coordination is close to octahedral (Table 1), with the maximum deviation (X—Co—Y) from 90° being 3.7 (2)°. The mean Co—O length, 2.063 Å, is consistent with reported Co—OH2 distances of tetraaqua complexes (2.060–2.124 Å) (Abrahams et al., 1996; de Meester & Skapski, 1973; Salas et al., 1992). Variations in the two Co—O bond lengths [0.15 (7) Å], although here barely significant, have been previously observed in tetraaquacobalt(II) complexes; for example, trans-tetraaquabis(adenine)cobalt(II) has Co—O bond lengths of 2.073 (4) and 2.114 (5) Å, which the authors attributed to different constraints imposed by hydrogen-bonding linkages (de Meester & Skapski, 1973).

All the coordinated water hydrogen atoms form hydrogen-bonds to adjacent bromide ions, creating a three-dimensional network (Fig. 2 and Table 2). Each bromide ion forms four hydrogen bonds in a distorted tetrahedral arrangement to different [Co(CH3CN)2(H2O)4]2+ cations with H···Br distances consistent with the reported distances of 2.30–2.68 Å (Mikenda, 1986; Tegenfeldt et al., 1979; Sieron & Bukowska-Strzyzewska, 1997). Three of the O—H.·Br angles are close to the most probable angle of 160° for a two-centre hydrogen bond (Jeffrey et al., 1985) while the fourth makes a smaller angle at the hydrogen, 135 (10)°, but with the Br···O contact the smallest at 3.283 (6) Å. The Br.·O distances range from 3.283 (6) to 3.315 Å compared with previously observed values between 3.195 (6) and 3.421 (3) Å (Kepert et al., 1996; Sieron & Bukowska-Strzyzewska, 1997; Cunningham et al., 1991).

As expected, the acetonitrile molecule is linear [N1—C1—C2 = 179.0 (6)°], but with bent coordination to the the cobalt(II) [Co—N1—C1 165.0 (4)°]. Such coordination has been observed in polymeric Co(O2PF2)2(CH3CN)2, 164.4° (Begley et al., 1985). Metal-acetonitrile bent coordination is indeed quite common with angles from 145.2 to 176.9°, and an average of 167°, having been reported (Agterberg et al., 1998; Begley et al., 1985; Chisholm et al., 1996; Holligan et al., 1992; Libby et al., 1993). This average is somewhat lowered by the two extreme low values for nickel(II) (Holligan et al., 1992) (145.2°) and manganese(III) (Libby et al., 1993) (149.1°) complexes, which have been attributed to hydrogen bonding and steric effects, respectively.

Experimental top

Crystals of [Co(CH3CN)2(H2O)4]Br2 were obtained after unintentional co-extraction of excess CoBr2, with CH2Cl2, from the reaction of excess CoBr2 with hexakis(2-pyridoxy)cyclotriphosphazene (prior to extraction with CH2Cl2, CH3CN solvent was evaporated from the reaction mixture).

Refinement top

The hydrogen atoms bound to O1 and O2 were located from a difference Fourier synthesis and refined unrestrained; methyl hydrogen atoms are in calculated positions. The residual electron-density maximum is 0.97 Å from Br1.

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT (Siemens, 1994) and SADABS (Sheldrick, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997b); molecular graphics: WinGX (Farrugia, 1998), ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 1990).

Figures top
[Figure 1] Fig. 1. [Co(CH3CN)2(H2O)4]2+ (ORTEP-3; Farrugia, 1997). Displacement ellipsoids are drawn at the 50% probability level and H atoms are of arbitrary size. Unlabelled atoms are related to labelled atoms by the inversion centre at Co1.
[Figure 2] Fig. 2. The three-dimensional network of O—H.·Br bonds in the structure of [Co(CH3CN)2(H2O)4]Br2 viewed down the a axis, b axis to the right. Some link atoms have been omitted for clarity.
(I) top
Crystal data top
[Co(CH3CN)2(H2O)4]Br2Z = 2
Mr = 372.92F(000) = 362
Monoclinic, P21/cDx = 1.917 Mg m3
a = 6.843 (4) ÅMo Kα radiation, λ = 0.71073 Å
b = 12.553 (7) ŵ = 7.50 mm1
c = 8.076 (5) ÅT = 158 K
β = 111.370 (8)°Block, pale brown
V = 646.0 (6) Å30.44 × 0.22 × 0.16 mm
Data collection top
CCD area detector
diffractometer
925 reflections with I > 2σ(I)
ϕ and ω scansRint = 0.056
Absorption correction: multi-scan
[SAINT (Siemens, 1994) and SADABS (Sheldrick, 1996)]
θmax = 26.4°, θmin = 3.2°
Tmin = 0.151, Tmax = 0.301h = 87
4724 measured reflectionsk = 615
1313 independent reflectionsl = 910
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)] = 0.038Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.087H atoms treated by a mixture of independent and constrained refinement
S = 0.90 w = 1/[σ2(Fo2) + (0.0515P)2]
where P = (Fo2 + 2Fc2)/3
1313 reflections(Δ/σ)max = 0.004
78 parametersΔρmax = 1.05 e Å3
0 restraintsΔρmin = 0.52 e Å3
Crystal data top
[Co(CH3CN)2(H2O)4]Br2V = 646.0 (6) Å3
Mr = 372.92Z = 2
Monoclinic, P21/cMo Kα radiation
a = 6.843 (4) ŵ = 7.50 mm1
b = 12.553 (7) ÅT = 158 K
c = 8.076 (5) Å0.44 × 0.22 × 0.16 mm
β = 111.370 (8)°
Data collection top
CCD area detector
diffractometer
1313 independent reflections
Absorption correction: multi-scan
[SAINT (Siemens, 1994) and SADABS (Sheldrick, 1996)]
925 reflections with I > 2σ(I)
Tmin = 0.151, Tmax = 0.301Rint = 0.056
4724 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0380 restraints
wR(F2) = 0.087H atoms treated by a mixture of independent and constrained refinement
S = 0.90Δρmax = 1.05 e Å3
1313 reflectionsΔρmin = 0.52 e Å3
78 parameters
Special details top

Refinement. Notes for referees. H atoms bound to O(1) and O(2) were located from a difference Fourier synthesis; methyl H atoms are in calculated positions. The O(1)—H(12) bond distance has refined to be "short" (Level C warning); however we consider there is no justification for constraining it (or the other O—H bond lengths) given satisfactory stereochemistry and a value which is reasonable given the bond e.s.d..

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Br10.80513 (9)0.36647 (4)0.09870 (7)0.02719 (19)
Co10.50000.00000.00000.0209 (3)
O10.6058 (9)0.1359 (4)0.0864 (7)0.0483 (14)
N10.3483 (7)0.0933 (3)0.1350 (6)0.0271 (10)
O20.7574 (7)0.0029 (5)0.2329 (6)0.0466 (13)
C10.2895 (9)0.1283 (4)0.2364 (7)0.0244 (11)
C20.2160 (9)0.1744 (5)0.3683 (7)0.0313 (13)
H2A0.23170.25200.36890.038*
H2B0.29890.14600.48600.038*
H2C0.06780.15630.33880.038*
H110.684 (10)0.193 (5)0.008 (9)0.05 (2)*
H120.644 (11)0.132 (5)0.148 (9)0.04 (2)*
H210.790 (11)0.038 (5)0.334 (9)0.048 (19)*
H220.803 (16)0.052 (8)0.260 (13)0.11 (4)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.0284 (3)0.0315 (3)0.0243 (3)0.0049 (3)0.0127 (2)0.0008 (2)
Co10.0218 (6)0.0248 (5)0.0189 (5)0.0007 (4)0.0109 (4)0.0009 (4)
O10.077 (4)0.035 (3)0.058 (3)0.017 (2)0.056 (3)0.015 (2)
N10.029 (3)0.028 (2)0.027 (3)0.0044 (19)0.014 (2)0.0027 (19)
O20.040 (3)0.064 (3)0.029 (3)0.020 (3)0.004 (2)0.016 (2)
C10.026 (3)0.028 (3)0.021 (3)0.000 (2)0.011 (2)0.001 (2)
C20.032 (3)0.036 (3)0.032 (3)0.006 (3)0.020 (3)0.003 (2)
Geometric parameters (Å, º) top
Co1—O2i2.056 (5)N1—C11.125 (6)
Co1—O22.056 (5)O2—H210.88 (7)
Co1—O12.071 (5)O2—H220.76 (10)
Co1—O1i2.071 (5)C1—C21.454 (7)
Co1—N1i2.112 (4)C2—H2A0.9800
Co1—N12.112 (4)C2—H2B0.9800
O1—H110.98 (7)C2—H2C0.9800
O1—H120.64 (6)
O2i—Co1—O2180.0 (2)Co1—O1—H11124 (4)
O2i—Co1—O189.7 (2)Co1—O1—H12119 (6)
O2—Co1—O190.3 (2)H11—O1—H12106 (7)
O2i—Co1—O1i90.3 (2)C1—N1—Co1164.9 (4)
O2—Co1—O1i89.7 (2)Co1—O2—H21134 (4)
O1—Co1—O1i180.0 (3)Co1—O2—H22112 (8)
O2i—Co1—N1i86.34 (18)H21—O2—H22104 (8)
O2—Co1—N1i93.66 (18)N1—C1—C2179.2 (6)
O1—Co1—N1i89.13 (19)C1—C2—H2A109.5
O1i—Co1—N1i90.87 (19)C1—C2—H2B109.5
O2i—Co1—N193.66 (18)H2A—C2—H2B109.5
O2—Co1—N186.34 (18)C1—C2—H2C109.5
O1—Co1—N190.87 (19)H2A—C2—H2C109.5
O1i—Co1—N189.13 (19)H2B—C2—H2C109.5
N1i—Co1—N1180.0 (3)
O2i—Co1—N1—C1139.2 (18)O1i—Co1—N1—C149.0 (18)
O2—Co1—N1—C140.8 (18)N1i—Co1—N1—C10 (18)
O1—Co1—N1—C1131.0 (18)Co1—N1—C1—C291.4 (18)
Symmetry code: (i) x+1, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H11···Br10.98 (7)2.38 (6)3.315 (6)161 (5)
O1—H12···Br1ii0.64 (7)2.65 (7)3.295 (6)175 (7)
O2—H21···Br1iii0.88 (7)2.42 (7)3.289 (5)169 (7)
O2—H22···Br1iv0.76 (10)2.70 (11)3.283 (6)135 (10)
Symmetry codes: (ii) x, y+1/2, z1/2; (iii) x, y+1/2, z+1/2; (iv) x+2, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formula[Co(CH3CN)2(H2O)4]Br2
Mr372.92
Crystal system, space groupMonoclinic, P21/c
Temperature (K)158
a, b, c (Å)6.843 (4), 12.553 (7), 8.076 (5)
β (°) 111.370 (8)
V3)646.0 (6)
Z2
Radiation typeMo Kα
µ (mm1)7.50
Crystal size (mm)0.44 × 0.22 × 0.16
Data collection
DiffractometerCCD area detector
diffractometer
Absorption correctionMulti-scan
[SAINT (Siemens, 1994) and SADABS (Sheldrick, 1996)]
Tmin, Tmax0.151, 0.301
No. of measured, independent and
observed [I > 2σ(I)] reflections
4724, 1313, 925
Rint0.056
(sin θ/λ)max1)0.626
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.038, 0.087, 0.90
No. of reflections1313
No. of parameters78
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)1.05, 0.52

Computer programs: SMART (Siemens, 1996), SMART, SAINT (Siemens, 1994) and SADABS (Sheldrick, 1996), SHELXS97 (Sheldrick, 1997a), SHELXL97 (Sheldrick, 1997b), WinGX (Farrugia, 1998), ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 1990).

Selected geometric parameters (Å, º) top
Co1—O22.056 (5)N1—C11.125 (6)
Co1—O12.071 (5)C1—C21.454 (7)
Co1—N12.112 (4)
O2—Co1—O190.3 (2)O1i—Co1—N189.13 (19)
O2—Co1—N186.34 (18)C1—N1—Co1164.9 (4)
O1—Co1—N190.87 (19)N1—C1—C2179.2 (6)
Symmetry code: (i) x+1, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H11···Br10.98 (7)2.38 (6)3.315 (6)161 (5)
O1—H12···Br1ii0.64 (7)2.65 (7)3.295 (6)175 (7)
O2—H21···Br1iii0.88 (7)2.42 (7)3.289 (5)169 (7)
O2—H22···Br1iv0.76 (10)2.70 (11)3.283 (6)135 (10)
Symmetry codes: (ii) x, y+1/2, z1/2; (iii) x, y+1/2, z+1/2; (iv) x+2, y1/2, z+1/2.
 

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