The substitution effect on heavy versions of cyclobutadiene

The structural and electronic characteristics of the M4R4 with M = C, Si, Ge and R = H, F, Cl, OH, MgH, BH2, NH2 Li are studied by ab initio calculations based on density functional theory using the hybrid B3LYP functional and 6-311++G* basis set. The results of natural bond orbital analysis (NBO), the analysis of structural parameters (bond lengths and bond angle, dihedral angle), atoms in molecules based theory (AIM) topological parameters such as the characteristics of bond critical points (electron densities and their Laplacians) leads to the conclusion that interamolecular interaction due with OH, MgH2, and NH2 substitutions are different from other derivatives. The cyclobutadiene ring and its heavy versions display very different geometrical structures. The cations and anions of C4R4, Si4R4, and Ge4R4 were studied to determine the effect of substitution on structure and stability. It has been shown that substitutions with ability of forming hydrogen bonds, bound to the silicon and germanium atoms are able to change the properties of the four-member rings more than the other substitutions. Comprehensive analyses of calculated NICS (nucleus-independent chemical shifts), polarizability, electrophilicity, and electron density are done. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010