On dicobaltpyromellitate-octadecahydrate (Co 2[C 6H 2(COO) 4]·18H 2O) — A compound with the novel chain-like polyanion Co(H 2O) 4[C 6H 2(COO) 4] 2n−n

Abstract

Red single crystals of Co 2[C 6H 2(COO) 4]·18H 2O were obtained in aqueous silicagel. They crystallise in the triclinic space group P1̄ with a=686.4(1), b=1000.0(2), c=1093.2(2) pm and α=93.00(2), β=104.86(1), γ=103.59(1) o . The crystal structure refinement converged to R g=0.0350 using 2766 X-ray diffraction intensities. Infinite chain-like polyanions extending parallel to [101] made up by Co 2+ cations and pyromellitate tetraanions with Co(H 2O) 4[C 6H 2(COO) 4] 2n− n stoichiometry are the prominent structural feature of Co 2[C 6H 2(COO) 4]·18H 2O. The Co 2+ ions of the polyanion are coordinated octahedrally by four water molecules situated in the equatorial plane of the coordination octahedron and two oxygen atoms belonging to carboxylate groups bound in trans-positions. Co(H 2O) 2+ 6 ions are intercalated between the chains in order to compensate for the negative excess charge of the polyanions. Further water molecules not coordinated to Co 2+ stabilise the crystal structure by hydrogen bonds.