The heats of formation of CIF, CIF(3), CIF(5), CIFO, CIFO(2), CIFO(3), CIF(3)O(2), CIF(3)O, and CIF(5)O have been calculated with the help of atomization reaction (AR), formation reaction (FR), and modified formation reaction (MFR) at the G3 and G3X (X = B3, MP2, and MP2B3) levels. FR or MFR in conjunction with the G3 theory can give accurate results close to experimental values. The standard thermodynamic functions of the title compounds have also been evaluated and the results agree well with the available experimental data. Results show that CIF, CIF(3), CIF(5) and CIF(3)O are stable at the room temperature, and CIFO(2), CIF(3)O(2), and CIF(5)O may be stable at lower temperature. (C) 2011 Elsevier B.V. All rights reserved.