Preparation, crystal structure and thermal stability of [(CH3)4N]2[Co(H2O)6](SeO4)2∙4H2O: A hydrogen bond stabilized hydrated double selenate

Abstract

A hydrated double selenate of tetramethylammonium and cobalt(II), [(CH3)4N]2[Co(H2O)6](SeO4)2∙4H2O, was crystalized from aqueous solution under controlled atmosphere and its crystal structure, vibrational properties and thermal stability were investigated by single crystal XRD, FTIR and thermogravimetric studies. Single crystal X-ray diffraction studies revealed an orthorhombic (space group Pca21) lattice with unit cell parameters a = 29.4027(4) Å, b = 6.4152(1) Å, c = 13.7442(2) Å, V = 2592.59(6) Å3 and Z = 4, for its crystal structure. The analyses of crystal structure indicated octahedral [Co(H2O)6] 2+ and tetrahedral (CH3)4N+ and SeO42─ entities in it. All these moieties were also confirmed by FTIR spectroscopy. These units are arranged in an open spacious architecture by 3D hydrogen bonding network, and the open spaces are further occupied by additional four water molecules. The stability of the structure is resulted from the though Co–O–H⋯O–Co, Co–O–H⋯O–Se, Se–O⋯H–O–H, H–O–H⋯O hydrogen bonds. The moisture content and temperature of the atmospheric environment were found to be crucial for its crystallization though a reproducible packing of the constituent groups. Thermal analysis (TG-DTG) of the double selenate revealed dehydration and then dissociation into individual salts. Subsequently the loss of organic moiety led to cobalt selenate and finally to cobalt oxide.