Synthesis, crystal and electronic structure of the new sodium chain sulfido cobaltates(II), Na3CoS3 and Na-5[CoS2](2)( Br)

摘要

The sulfido cobaltate(II) Na3CoS3 was synthesized from stoichiometric quantities of Na2S, elemental cobalt and sulfur at a maximum temperature of 1100 degrees C. According to Na3CoS3 = Na-12[Co2S5(S-2)][Co2S3(S-2)] the orthorhombic structure of a new type (space group Cmc2(1), 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(S-2)](8-) of two edge-sharing [CoS4] tetrahedra with five sulfido and one eta(1)-disulfido ligand; ii. chains (1)(infinity)[Co2S5(S-2)](4-) of [CoS4] tetrahedra connected via mu-sulfido (3x) besides mu-1,2-disulfido (1x) ligands. The second title compound, Na-5[CoS2](2)(Br), which has been likewise synthesized as a pure phase from stoichiometric quantities of Na2S, Co, S and NaBr, is isotypic to Na-5[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)(infinity)[CoS4/2](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 Na-5[CoS2](2)(SH) was obtained via the addition of NaSH. Several synthetic and structural arguments suggest that Na-5[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 Na-5[CoS2]. They also allow for obtaining insight into the superexchange path, which is responsible for the strong antiferromagnetic Co spin ordering along the chains.