Energy Analysis of the Chemical Bond in Group IV and V Complexes: A Density Functional Theory Study O. KH. POLESHCHUK, 1 E. L. SHEVCHENKO, 1 V. BRANCHADELL, 2 M. LEIN, 3 G. FRENKING 3 1 Tomsk State Pedagogical University, 634041, Komsomolskii 75, Tomsk, Russia 2 Departament de Quı ´mica, Universitat Autonoma de Barcelona, Edifici Cn, 08193 Bellaterra, Spain 3 Philipps-Universita ¨t Marburg, Marburg D-35032, Germany Received 7 September 2003; accepted 17 March 2004 Published online 13 October 2004 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/qua.20348 ABSTRACT: We analyzed the chemical bond between antimony, tin, titanium, and niobium chlorides with several Lewis bases using an energy partitioning analysis (EPA) and Weinhold’s NBO method. The optimized geometries are in good agreement with the experimental results. The NQR- 35 Cl frequencies appear to be fairly close to the experimental values. Theoretically obtained nuclear quadrupole coupling constants of antimony and niobium atoms are in good agreement with the experimental values. The bonding energies and experimentally known heats of formation are well reproduced by the employed level of theory. All investigated bonds in the donor-acceptor complexes are highly polar, so that the Townes-Dailey theory cannot be applied. The NBO approach shows that the donor– acceptor interactions of main-group elements such as Sb and Sn can basically be described in terms of sp hybridization, just as these interactions of the transition metal elements Ti and Nb can be described by sd hybridization. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem 101: 869 – 877, 2005 Key words: organic ligands; DFT calculations; donor-acceptor complexes; nuclear quadrupole coupling constants Introduction C ompounds of nontransition and transition el- ements containing tin, antimony, titanium, and niobium atoms have been of considerable in- terest for nuclear quadrupole resonance spectros- copy (NQR) and the Mo ¨ ssbauer effect [1–5] for quite some time. Parameters such as quadrupole splitting or nuclear quadrupole coupling constant (NQCC) as well as Mo ¨ ssbauer isomeric shifts on the Correspondence to: O. Kh. Poleshchuk; e-mail: poleshch@tspu. edu.ru Contract grant sponsor: Deutscher Akademischer Austausch Dienst (DAAD). This article contains supplementary material available via the Internet at http://www.interscience.wiley.com/jpages/0020- 7608/suppmat. International Journal of Quantum Chemistry, Vol 101, 869 – 877 (2005) © 2004 Wiley Periodicals, Inc.