A systematic investigation of the X 2 CTe and XYCTe (X,Y = H, F, Cl, Br, I and CN) species is carried out using the second-order Møller-Plesset perturbation theory and density functional theory. The basis sets used for all atoms (except iodine and tellurium) in this work are of double-f plus polarization quality with additional s-and p-type diffuse functions and denoted DZP??. The LANL2DZdp ECP and 6-311G(d,p) basis sets are used for tellurium and iodine. Vibrational frequency analyses are performed to evaluate zero-point energy corrections and to determine the nature of the stationary points located. The ionization potentials (IP ad and IP ad(ZPVE) ), the four different forms of neutral-anion separations (EA ad , EA ad(ZPVE) , VEA and VDE), the singlet-triplet splittings as well as the HOMO-LUMO gaps are predicted. The electronegativity (v) reactivity descriptor for the halogens (F, Cl, Br and I) and the calculated Mulliken's electronegativity are used as tools to assess the interrelated properties of these telluroformaldehyde derivatives. The predicted IP ad(ZPVE) values with the B3LYP functional range from 7.89 [I 2 CTe] to 9.16 eV [F(NC)CTe], the EA ad(ZPVE) ranges from 1.29 [I 2 CTe] to 3.34 eV [(NC) 2 CTe], the singlet-triplet splitting ranges from 0.64 [H(NC)CTe)] to 1.85 eV [F 2 CTe], and the HOMO-LUMO gap ranges from 2.21 [H(NC)CTe] to 3.42 eV [F 2 CTe]. The HOMO-LUMO gap is found to be proportional to the singlet-triplet splitting. The results obtained are critically analyzed and discussed. This research is also compared with analogous studies of formaldehyde, thioformaldehyde and selenoformadehyde.

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The unavailability of monomeric heavy ketone analogues has been ascribed to the evanescence of the very reactive A═E double bond (A and E are the heavier group 14 and group 16 elements, respectively). Can the isolation of any of the monomeric telluro-ketones be assisted by an energetic favorability on its potential energy surface (PES)? In this light, the reaction pathways for the isomerization and decomposition reactions of H2A═Te and HFA═Te (A = C, Si, and Ge) molecules on their singlet state PES have been studied using second-order Møller-Plesset perturbation theory (MP2). The barrier heights reported suggest that telluroformaldehyde, silanetellone, and germatellone are kinetically more resistant to unimolecular reactions than the corresponding lighter chalcogen analogues. However, upon replacing a hydrogen atom by fluorine, the barrier heights of most of the isomerization and decomposition reactions are lowered. Among the unimolecular reactions studied for the H2A═Te and HFA═Te (A = C, Si, and Ge) molecules, the decomposition of cis-FGeTeH into HF and GeTe is found to be the most facile reaction, with a barrier height of only 4.6 kcal/mol. We also predict the ground state telluro-ketones to be viable molecules, as they have no imaginary vibrational frequencies and their lowest vibrational frequencies are always >100 cm(-1). In view of the scarcity of information on the chemistry of the mentioned telluro-ketones, the molecular parameters of various isomers and decomposition products have been reported, and should be useful for future experimental investigations.

No stable germanetellone was described until Tbt(Dis)Ge=Te and Tbt(Tip)Ge=Te (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Dis = bis(trimethylsilyl)methyl and Tip = 2,4,6-triisopropylphenyl) were reported in 1997. Following these initial experiments, there has arisen considerable interest in Ge[double bond, length as m-dash]Te systems. An obvious question is: why have the simple XYGe=Te (X, Y = H, F, Cl, Br, I and CN) molecules not yet been isolated? In view of the present situation, theoretical information may be of great help for further advances in germanetellone chemistry. A systematic investigation of the XYGe=Te molecules is carried out using the second order Møller-Plesset perturbation theory (MP2) and density functional theory (DFT). The structures and energetics, including ionization potentials (IPad and IPad(ZPVE)), four different forms of neutral-anion separations (EAad, EAad(ZPVE), VEA and VDE) and the singlet-triplet gaps, are reported. The electronegativity (χ) reactivity descriptor for the halogens (F, Cl, Br and I) and the natural charge separations of the Ge=Te moiety are used to assess the interrelated properties of germanetellone and its derivatives. The results are analyzed, discussed and compared with analogous studies of telluroformaldehyde, silanetellone and their derivatives. The thermodynamic viabilities of some of the novel germanetellones have also been evaluated in terms of the bond dissociation enthalpies of Tbt(Dis)Ge=Te and Tbt(Tip)Ge=Te. The simple mono-substituted germanetellones appear to be slightly more thermodynamically favored than Tbt(Dis)Ge=Te and Tbt(Tip)Ge=Te, since the bond dissociation enthalpies of these kinetically stabilized germanetellones are about 28 and 51 kcal mol(-1) lower, respectively.