Green coloured single crystals of [trans-Co(en)(2)Cl-2]IO4 I and dark red coloured single crystals of [trans-Co(en)(2)(N-3)(2)]N-3 II were obtained by slowly mixing stoichiometric quantities of the separately dissolved trans-diclilorobis(ethylenediamine)cobalt(III) chloride with sodium metaperiodate or sodium azide in aqueous medium. Elemental analyses, spectroscopic studies (IR, UV/visible, H-1 and C-13 NMR) and solubility measurements were performed to characterize the complex salts. The compound I crystallizes in the monoclinic space group P2(1)/c with a= 6.3970(2), b = 16.6790(4), c = 12.3730(3) angstrom, beta = 99.148(1)degrees, V=1303.35(6) angstrom(3), Z=4 and II crystallizes in the orthorhombic space group Pbca with a = 10.1790(1), b = 13.5350(1), c = 17.2410(2) angstrom, V= 2375.34(4))angstrom, Z = 8. Supramolecular hydrogen bonding networks between ionic groups [NHen+ ... X-anion(-)] by second sphere coordination besides electrostatic forces of attraction have been observed. Compound II represents the first reported structure of a salt containing the cation, [trans-Co(en)(2)(N-3)(2)](+) (c) 2006 Elsevier B.V. All rights reserved.