A coordination polymer was synthesized by the reaction of CoCl2 with 1,2,4-triazole-5-one (TO) and charaterized by means of IR and TG-DTG. Single-crystal structure analysis showed that the complex crystallized in the monoclinic space group C2/c: a = 23.105(9) angstrom, b = 3.5683(2) angstrom, c = 13.589(6) angstrom, alpha = 90 degrees, beta = 124.038(4)degrees, gamma = 90 degrees, V= 928.4(7) angstrom(3), Z = 4. The standard molar enthalpy of formation of the complex was determined to be (-1034.28 +/- 0.95)kJmol(-1). (c) 2007 Elsevier B.V. All rights reserved.