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metal-organic compounds
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Diaquabis(dimethyl sulfoxide-κO)bis(saccharinato-κN)cobalt(II)
aSchool of Chemistry, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban 4000, South Africa
*Correspondence e-mail: vanzylw@ukzn.ac.za
The title complex, [Co(C7H4NO3S)2(C2H6OS)2(H2O)2], contains a Co2+ cation in an octahedral coordination environment. The metal atom is surrounded by two different neutral ligands, namely dimethylsulfoxide (DMSO) and water, each coordinating through the O atom. The anionic saccharinate (sac; 1,1,3-trioxo-2,3-dihydro-1λ6,2-benzothiazol-2-ide) ligand coordinates through the N atom. Each of the three similar ligand pairs is in a trans configuration with respect to each other. The Co atom lies on a crystallographic center of symmetry and the octahedral geometry is not significantly distorted. A short O—H⋯O hydrogen bond is present between a water H atom and the ketone O atom; two longer hydrogen bonds (intra- and intermolecular) are also present between a water H and a sulfonic O atom, forming a supramolecular assembly through head-to-tail aggregation between adjacent complexes.
Related literature
For a general review article on the coordination chemistry of saccharinate ligands, see: Baran & Yilmaz (2006). For cobalt(II) saccharinate complexes, see: Deng et al. (2008
) and for cobalt(II) complexes with saccharinate as a non-coordinating ligand, see: Batsanov et al. (2011
). For the preparation of cobalt(II) and other divalent metal precursor complexes, see: Haider et al. (1985
).
Experimental
Crystal data
|
Refinement
|
|
Data collection: COLLECT (Nonius, 1998); cell DENZO-SMN (Otwinowski & Minor, 1997
); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008
); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008
); molecular graphics: SHELXTL (Sheldrick, 2008
); software used to prepare material for publication: SHELXL97.
Supporting information
https://doi.org/10.1107/S1600536811045296/br2180sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536811045296/br2180Isup2.hkl
[Co(sac)2(H2O)4].2H2O was prepared as per literature method (Haider et al., 1985). The red crystals of [Co(sac)2(H2O)4].2H2O (0.932 g; 1.80 mmol) was placed in a 100 ml beaker and dissolved in excess amount of dimethyl sulfoxide (dmso) (20 ml). The reaction mixture was gently heated on a heating plate with stirring to reduce the volume of dmso to ~7 ml. The beaker was removed from the heat source and allowed to stand for 10 days during which time large light red blocky crystals of the title compound were obtained. Yield (1.00 g, 93.0%). Mp: 393 K; 120 ° C. IR-ATR (cm-1): 3486.98, 3005.41 n(OH); 1618 n(C=O); 1584, 1460 n(C=C); 1256 n(O=S=O); 1141, 949 n(S=O). No NMR data were recorded due to the paramagnetic nature of the Co(II) complex. Single crystals were obtained by slow evaporation of dmso solvent.
All hydrogen atoms could be found in the difference electron density maps. All, except H5A and H5B on O5, were placed in idealised positions refining in riding models with Uiso set at 1.2 or 1.5 times those of their parent atoms. The water hydrogen atoms H5A and H5B were located in the difference electron density maps and refined with independent isotropic temperature factors and simple bond length constraints of d(O-H) = 0.980 (2) Å.
Saccharin (o-sulfobenzimide; 1,2-benzothiazole-3(2H)-one 1,1-dioxide; Hsac) is a widely used artificial sweetening agent. The imino hydrogen is acidic and can be readily deprotonated. The coordination chemistry of this anion is versatile due to the different coordination sites to metallic centers it can accommodate, i.e., one N, one O (carbonylic) and two O (sulfonic) atoms. These donor atoms of the anion can thus readily generate either N– or O-monodentate or bidentate (N, O) coordination. Saccharin is normally used as the sodium or calcium salt which dramatically improves water solubility. Most metal complexes contain the deprotonated form of saccharin, and this saccharinate anion (sac) is commercially available as the sodium salt, used in the present study. The reaction of sodium saccharinate with the first row divalent transition metal ions results in coordination complexes with general formula [M(sac)2(H2O)4].2H2O, (M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn), which all show a clear preference to bind through the deprotonated anionic N-atom (Baran and Yilmaz, 2006). These octahedral complexes contain two N-bonded sac ligands in trans positions, and complexes of the type [M(sac)2(H2O)4].2H2O are thus commonly used as precursors in the synthesis of mixed-ligand saccharinate complexes. The aqua ligands in these metal complexes are labile and readily displaced by direct reaction of neutral ligands. The addition of the ligands to the solutions of the complexes usually results in the substitution of all four aqua ligands, thereby forming stable new mixed-ligand complexes. In cases where the incoming neutral ligand is relatively bulky, as in the present study, it causes
and only two of the four aqua ligands become displaced in order for the Co center to remain octahedral. Although there are a number of Co(II) saccharinate complexes previously reported (Batsanov et al., 2011, and refs. therein), the present study reports the first example of a structurally characterized Co(II) complex that contains both saccharinate and dmso ligands.For a general review article on the coordination chemistry of saccharinate ligands, see: Baran & Yilmaz (2006). For cobalt(II) saccharinate complexes, see: Deng et al. (2008) and for cobalt(II) complexes with saccharinate as a non-coordinating ligand, see: Batsanov et al. (2011). For the preparation of cobalt(II) and other divalent metal precursor complexes, see: Haider et al. (1985).
Data collection: COLLECT (Nonius, 1998); cell
DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008). ![]() | Fig. 1. The ORTEP molecular structure of the title complex, shown with 50% probability ellipsoids. |
[Co(C7H4NO3S)2(C2H6OS)2(H2O)2] | F(000) = 634 |
Mr = 615.56 | Dx = 1.695 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 5888 reflections |
a = 10.2304 (3) Å | θ = 2.4–28.3° |
b = 15.1418 (6) Å | µ = 1.12 mm−1 |
c = 7.8615 (3) Å | T = 173 K |
β = 98.068 (2)° | Block, light red |
V = 1205.75 (8) Å3 | 0.27 × 0.15 × 0.10 mm |
Z = 2 |
Nonius KappaCCD diffractometer | 3000 independent reflections |
Radiation source: fine-focus sealed tube | 2301 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.018 |
1.2° φ scans and ω scans | θmax = 28.3°, θmin = 2.4° |
Absorption correction: multi-scan (SADABS; Bruker, 2001) | h = −13→13 |
Tmin = 0.753, Tmax = 0.897 | k = −20→20 |
5888 measured reflections | l = −10→10 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.030 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.081 | w = 1/[σ2(Fo2) + (0.0497P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.06 | (Δ/σ)max < 0.001 |
3000 reflections | Δρmax = 0.71 e Å−3 |
171 parameters | Δρmin = −0.49 e Å−3 |
2 restraints | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0082 (11) |
[Co(C7H4NO3S)2(C2H6OS)2(H2O)2] | V = 1205.75 (8) Å3 |
Mr = 615.56 | Z = 2 |
Monoclinic, P21/c | Mo Kα radiation |
a = 10.2304 (3) Å | µ = 1.12 mm−1 |
b = 15.1418 (6) Å | T = 173 K |
c = 7.8615 (3) Å | 0.27 × 0.15 × 0.10 mm |
β = 98.068 (2)° |
Nonius KappaCCD diffractometer | 3000 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2001) | 2301 reflections with I > 2σ(I) |
Tmin = 0.753, Tmax = 0.897 | Rint = 0.018 |
5888 measured reflections |
R[F2 > 2σ(F2)] = 0.030 | 2 restraints |
wR(F2) = 0.081 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.06 | Δρmax = 0.71 e Å−3 |
3000 reflections | Δρmin = −0.49 e Å−3 |
171 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
Co1 | 0.5000 | 0.5000 | 0.0000 | 0.01579 (11) | |
S1 | 0.27267 (4) | 0.50687 (3) | 0.28359 (5) | 0.01976 (12) | |
S2 | 0.51966 (4) | 0.68690 (3) | 0.19988 (6) | 0.02130 (13) | |
O1 | 0.37735 (12) | 0.46878 (9) | 0.40314 (15) | 0.0278 (3) | |
O2 | 0.24179 (13) | 0.59763 (9) | 0.31675 (17) | 0.0305 (3) | |
O3 | 0.18849 (12) | 0.43540 (8) | −0.16410 (15) | 0.0251 (3) | |
O4 | 0.51937 (12) | 0.63688 (8) | 0.03114 (15) | 0.0222 (3) | |
O5 | 0.60377 (12) | 0.47674 (8) | 0.24012 (16) | 0.0218 (3) | |
H5A | 0.6902 (13) | 0.5053 (17) | 0.246 (4) | 0.087 (11)* | |
H5B | 0.570 (3) | 0.4869 (16) | 0.3492 (18) | 0.062 (8)* | |
N1 | 0.30080 (14) | 0.49352 (9) | 0.08660 (19) | 0.0193 (3) | |
C1 | 0.13015 (16) | 0.44084 (11) | 0.2695 (2) | 0.0192 (4) | |
C2 | 0.05764 (17) | 0.41415 (12) | 0.3962 (2) | 0.0240 (4) | |
H2 | 0.0820 | 0.4307 | 0.5129 | 0.029* | |
C3 | −0.05215 (19) | 0.36209 (12) | 0.3448 (3) | 0.0296 (4) | |
H3 | −0.1056 | 0.3433 | 0.4275 | 0.036* | |
C4 | −0.08537 (19) | 0.33692 (14) | 0.1742 (3) | 0.0324 (5) | |
H4 | −0.1611 | 0.3010 | 0.1428 | 0.039* | |
C5 | −0.01053 (17) | 0.36300 (12) | 0.0487 (2) | 0.0259 (4) | |
H5 | −0.0334 | 0.3452 | −0.0676 | 0.031* | |
C6 | 0.09874 (16) | 0.41590 (11) | 0.0990 (2) | 0.0196 (4) | |
C7 | 0.19847 (16) | 0.44925 (11) | −0.0076 (2) | 0.0192 (4) | |
C8 | 0.39348 (18) | 0.76726 (13) | 0.1549 (2) | 0.0296 (4) | |
H8A | 0.4055 | 0.7992 | 0.0498 | 0.044* | |
H8B | 0.3981 | 0.8089 | 0.2509 | 0.044* | |
H8C | 0.3072 | 0.7380 | 0.1391 | 0.044* | |
C9 | 0.65935 (19) | 0.75778 (13) | 0.2148 (3) | 0.0348 (5) | |
H9A | 0.7402 | 0.7223 | 0.2331 | 0.052* | |
H9B | 0.6581 | 0.7985 | 0.3114 | 0.052* | |
H9C | 0.6567 | 0.7915 | 0.1080 | 0.052* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Co1 | 0.01863 (18) | 0.01480 (18) | 0.01393 (18) | −0.00075 (12) | 0.00224 (13) | −0.00099 (12) |
S1 | 0.0190 (2) | 0.0247 (2) | 0.0160 (2) | −0.00384 (16) | 0.00399 (17) | −0.00383 (16) |
S2 | 0.0269 (2) | 0.0180 (2) | 0.0189 (2) | −0.00124 (17) | 0.00312 (17) | −0.00226 (17) |
O1 | 0.0216 (7) | 0.0433 (8) | 0.0182 (7) | −0.0027 (6) | 0.0013 (5) | −0.0020 (6) |
O2 | 0.0354 (8) | 0.0253 (7) | 0.0324 (8) | −0.0053 (6) | 0.0103 (6) | −0.0102 (6) |
O3 | 0.0246 (6) | 0.0333 (7) | 0.0172 (6) | −0.0048 (5) | 0.0023 (5) | −0.0029 (5) |
O4 | 0.0319 (7) | 0.0156 (6) | 0.0195 (6) | −0.0010 (5) | 0.0049 (5) | −0.0023 (5) |
O5 | 0.0237 (7) | 0.0248 (6) | 0.0169 (6) | −0.0007 (5) | 0.0034 (5) | 0.0001 (5) |
N1 | 0.0181 (7) | 0.0241 (8) | 0.0162 (7) | −0.0029 (6) | 0.0042 (6) | −0.0019 (6) |
C1 | 0.0188 (8) | 0.0185 (8) | 0.0202 (9) | 0.0005 (7) | 0.0026 (7) | −0.0017 (7) |
C2 | 0.0255 (9) | 0.0261 (9) | 0.0216 (9) | 0.0020 (8) | 0.0077 (8) | −0.0009 (8) |
C3 | 0.0288 (10) | 0.0325 (11) | 0.0301 (11) | −0.0060 (8) | 0.0129 (8) | 0.0005 (8) |
C4 | 0.0263 (10) | 0.0361 (11) | 0.0351 (11) | −0.0113 (9) | 0.0057 (8) | −0.0021 (9) |
C5 | 0.0231 (9) | 0.0301 (11) | 0.0237 (9) | −0.0043 (7) | 0.0005 (8) | −0.0050 (8) |
C6 | 0.0180 (8) | 0.0205 (9) | 0.0200 (9) | 0.0017 (7) | 0.0019 (7) | 0.0004 (7) |
C7 | 0.0189 (8) | 0.0209 (9) | 0.0176 (9) | 0.0022 (7) | 0.0022 (7) | 0.0011 (7) |
C8 | 0.0351 (11) | 0.0248 (10) | 0.0291 (11) | 0.0070 (8) | 0.0049 (9) | −0.0041 (8) |
C9 | 0.0332 (11) | 0.0313 (11) | 0.0399 (12) | −0.0098 (9) | 0.0058 (9) | −0.0143 (9) |
Co1—O5i | 2.0620 (12) | C1—C2 | 1.383 (2) |
Co1—O5 | 2.0620 (12) | C1—C6 | 1.386 (2) |
Co1—O4i | 2.0932 (12) | C2—C3 | 1.385 (3) |
Co1—O4 | 2.0932 (12) | C2—H2 | 0.9500 |
Co1—N1i | 2.2396 (14) | C3—C4 | 1.390 (3) |
Co1—N1 | 2.2396 (14) | C3—H3 | 0.9500 |
S1—O2 | 1.4420 (14) | C4—C5 | 1.389 (3) |
S1—O1 | 1.4423 (13) | C4—H4 | 0.9500 |
S1—N1 | 1.6270 (15) | C5—C6 | 1.387 (2) |
S1—C1 | 1.7586 (17) | C5—H5 | 0.9500 |
S2—O4 | 1.5272 (12) | C6—C7 | 1.496 (2) |
S2—C8 | 1.7731 (18) | C8—H8A | 0.9800 |
S2—C9 | 1.7779 (18) | C8—H8B | 0.9800 |
O3—C7 | 1.2383 (19) | C8—H8C | 0.9800 |
O5—H5A | 0.980 (2) | C9—H9A | 0.9800 |
O5—H5B | 0.980 (2) | C9—H9B | 0.9800 |
N1—C7 | 1.370 (2) | C9—H9C | 0.9800 |
O5i—Co1—O4i | 91.94 (5) | C1—C2—C3 | 116.79 (17) |
O5—Co1—O4i | 88.06 (5) | C1—C2—H2 | 121.6 |
O5i—Co1—O4 | 88.06 (5) | C3—C2—H2 | 121.6 |
O5—Co1—O4 | 91.94 (5) | C2—C3—C4 | 121.08 (18) |
O5i—Co1—N1i | 95.03 (5) | C2—C3—H3 | 119.5 |
O5—Co1—N1i | 84.97 (5) | C4—C3—H3 | 119.5 |
O4i—Co1—N1i | 94.77 (5) | C5—C4—C3 | 121.56 (18) |
O4—Co1—N1i | 85.23 (5) | C5—C4—H4 | 119.2 |
O5i—Co1—N1 | 84.97 (5) | C3—C4—H4 | 119.2 |
O5—Co1—N1 | 95.03 (5) | C6—C5—C4 | 117.63 (17) |
O4i—Co1—N1 | 85.23 (5) | C6—C5—H5 | 121.2 |
O4—Co1—N1 | 94.77 (5) | C4—C5—H5 | 121.2 |
O2—S1—O1 | 115.14 (8) | C1—C6—C5 | 120.11 (16) |
O2—S1—N1 | 111.29 (8) | C1—C6—C7 | 111.46 (14) |
O1—S1—N1 | 110.87 (8) | C5—C6—C7 | 128.36 (16) |
O2—S1—C1 | 110.64 (8) | O3—C7—N1 | 124.77 (15) |
O1—S1—C1 | 110.29 (8) | O3—C7—C6 | 122.14 (15) |
N1—S1—C1 | 97.19 (8) | N1—C7—C6 | 113.08 (14) |
O4—S2—C8 | 104.73 (8) | S2—C8—H8A | 109.5 |
O4—S2—C9 | 105.08 (8) | S2—C8—H8B | 109.5 |
C8—S2—C9 | 98.91 (10) | H8A—C8—H8B | 109.5 |
S2—O4—Co1 | 125.54 (7) | S2—C8—H8C | 109.5 |
Co1—O5—H5A | 108.2 (18) | H8A—C8—H8C | 109.5 |
Co1—O5—H5B | 125.2 (16) | H8B—C8—H8C | 109.5 |
H5A—O5—H5B | 108 (2) | S2—C9—H9A | 109.5 |
C7—N1—S1 | 110.58 (11) | S2—C9—H9B | 109.5 |
C7—N1—Co1 | 121.08 (11) | H9A—C9—H9B | 109.5 |
S1—N1—Co1 | 125.03 (8) | S2—C9—H9C | 109.5 |
C2—C1—C6 | 122.81 (16) | H9A—C9—H9C | 109.5 |
C2—C1—S1 | 130.12 (14) | H9B—C9—H9C | 109.5 |
C6—C1—S1 | 107.07 (12) |
Symmetry code: (i) −x+1, −y+1, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
O5—H5A···O3i | 0.98 | 1.73 | 2.646 (2) | 155 (3) |
O5—H5B···O1 | 0.98 | 2.09 | 2.803 (2) | 128 (2) |
O5—H5B···O1ii | 0.98 | 2.06 | 2.904 (2) | 143 (2) |
C8—H8B···O5iii | 0.98 | 2.54 | 3.277 (2) | 132 |
C8—H8B···O4iv | 0.98 | 2.51 | 3.383 (2) | 148 |
C9—H9A···O3i | 0.98 | 2.58 | 3.363 (2) | 137 |
C9—H9B···O4iv | 0.98 | 2.58 | 3.432 (2) | 146 |
Symmetry codes: (i) −x+1, −y+1, −z; (ii) −x+1, −y+1, −z+1; (iii) −x+1, y+1/2, −z+1/2; (iv) x, −y+3/2, z+1/2. |
Experimental details
Crystal data | |
Chemical formula | [Co(C7H4NO3S)2(C2H6OS)2(H2O)2] |
Mr | 615.56 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 173 |
a, b, c (Å) | 10.2304 (3), 15.1418 (6), 7.8615 (3) |
β (°) | 98.068 (2) |
V (Å3) | 1205.75 (8) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 1.12 |
Crystal size (mm) | 0.27 × 0.15 × 0.10 |
Data collection | |
Diffractometer | Nonius KappaCCD |
Absorption correction | Multi-scan (SADABS; Bruker, 2001) |
Tmin, Tmax | 0.753, 0.897 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5888, 3000, 2301 |
Rint | 0.018 |
(sin θ/λ)max (Å−1) | 0.667 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.030, 0.081, 1.06 |
No. of reflections | 3000 |
No. of parameters | 171 |
No. of restraints | 2 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.71, −0.49 |
Computer programs: COLLECT (Nonius, 1998), DENZO-SMN (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
O5—H5A···O3i | 0.98 | 1.73 | 2.646 (2) | 155 (3) |
O5—H5B···O1 | 0.98 | 2.09 | 2.803 (2) | 127.9 (19) |
O5—H5B···O1ii | 0.98 | 2.06 | 2.904 (2) | 143 (2) |
C8—H8B···O5iii | 0.98 | 2.54 | 3.277 (2) | 132.00 |
C8—H8B···O4iv | 0.98 | 2.51 | 3.383 (2) | 148.00 |
C9—H9A···O3i | 0.98 | 2.58 | 3.363 (2) | 137.00 |
C9—H9B···O4iv | 0.98 | 2.58 | 3.432 (2) | 146.00 |
Symmetry codes: (i) −x+1, −y+1, −z; (ii) −x+1, −y+1, −z+1; (iii) −x+1, y+1/2, −z+1/2; (iv) x, −y+3/2, z+1/2. |
Acknowledgements
WEvZ gratefully acknowledges financial support from the University of KwaZulu-Natal. FSWP thanks the National Research Foundation (NRF) for an Innovative Grant.
References
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Saccharin (o-sulfobenzimide; 1,2-benzothiazole-3(2H)-one 1,1-dioxide; Hsac) is a widely used artificial sweetening agent. The imino hydrogen is acidic and can be readily deprotonated. The coordination chemistry of this anion is versatile due to the different coordination sites to metallic centers it can accommodate, i.e., one N, one O (carbonylic) and two O (sulfonic) atoms. These donor atoms of the anion can thus readily generate either N– or O-monodentate or bidentate (N, O) coordination. Saccharin is normally used as the sodium or calcium salt which dramatically improves water solubility. Most metal complexes contain the deprotonated form of saccharin, and this saccharinate anion (sac) is commercially available as the sodium salt, used in the present study. The reaction of sodium saccharinate with the first row divalent transition metal ions results in coordination complexes with general formula [M(sac)2(H2O)4].2H2O, (M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn), which all show a clear preference to bind through the deprotonated anionic N-atom (Baran and Yilmaz, 2006). These octahedral complexes contain two N-bonded sac ligands in trans positions, and complexes of the type [M(sac)2(H2O)4].2H2O are thus commonly used as precursors in the synthesis of mixed-ligand saccharinate complexes. The aqua ligands in these metal complexes are labile and readily displaced by direct reaction of neutral ligands. The addition of the ligands to the solutions of the complexes usually results in the substitution of all four aqua ligands, thereby forming stable new mixed-ligand complexes. In cases where the incoming neutral ligand is relatively bulky, as in the present study, it causes steric hindrance and only two of the four aqua ligands become displaced in order for the Co center to remain octahedral. Although there are a number of Co(II) saccharinate complexes previously reported (Batsanov et al., 2011, and refs. therein), the present study reports the first example of a structurally characterized Co(II) complex that contains both saccharinate and dmso ligands.