Synthesis, crystal and electronic structure of the new sodium chain sulfido cobaltates(II), Na3CoS3 and Na5[CoS2]2(Br)

Abstract

Abstract The sulfido cobaltate(II) Na3CoS3 was synthesized from stoichiometric quantities of Na2S, elemental cobalt and sulfur at a maximum temperature of 1100°C. According to Na3CoS3=Na12[Co2S5(S2)][Co2S3(S2)] the orthorhombic structure of a new type (space group Cmc21, a=884.24(2), b=2177.38(5), c=1193.20(3) pm, Z=12, R1=0.0205) contains two different anions: i. dimers [Co2S5(S2)]8− of two edge-sharing [CoS4] tetrahedra with five sulfido and one η 1-disulfido ligand; ii. chains ∞ 1 [ Co 2 S 3 ( S 2 ) ] 4 − $_\infty ^1{[{\rm{C}}{{\rm{o}}_2}{{\rm{S}}_3}({{\rm{S}}_2})]^{4 - }}$ of [CoS4] tetrahedra connected via μ-sulfido (3×) besides μ-1,2-disulfido (1×) ligands. The second title compound, Na5[CoS2]2(Br), which has been likewise synthesized as a pure phase from stoichiometric quantities of Na2S, Co, S and NaBr, is isotypic to Na5[CoS2]2(S) (Na6PbO5 type; tetragonal, space group I4mm, a=914.58(7), c=625.59(5) pm; R1=0.0412). The structure contains linear chains ∞ 1 [ CoS 4 / 2 ] 2 − $_\infty ^1{[{\rm{Co}}{{\rm{S}}_{4/2}}]^{2 - }}$ running along the tetragonal c axis. In between, Br− ions are interspersed, which are coordinated by square pyramids of Na+ ions. The isotypic hydrogensulfide Na5[CoS2]2(SH) was obtained via the addition of NaSH. Several synthetic and structural arguments suggest that Na5[CoS2]2(SH) and the previously described pure sulfide are the same compound. The results of DFT band structure calculations (GGA+U, AFM spin ordering) are used to discuss and compare the chemical bonding in the new sulfido cobaltates(II) with that of the reference compound Na2[CoS2]. They also allow for obtaining insight into the superexchange path, which is responsible for the strong antiferromagnetic Co spin ordering along the chains.