Theoretical studies of the preferred connectivity in X3NZ (X = H, F; Z = O, S) types of molecules

B3LYP/6-311+G* calculations were performed on a series of structural isomers of nitrosyl trifluoride (1a), thiazyl trifluoride (3d), and their hydrogen analogues (2 and 4). Computational results show that the most stable isomeric form varies among the four series. For example, in the hydride series, the molecule with the formula H(2)NZH, with Z being either O or S, has the highest thermal stability. In contrast, the most stable isomers in the two fluoride series were found to be F3NO and cis-FNSF2. The relative energetics and the structural differences among the constitutional isomers in each series, as well as those between the isovalent series, are discussed. Natural bond orbital analysis results are presented, and new structures for F3NO and F3NS are proposed. (C) 2002 Elsevier Science B.V. All rights reserved.