ORIGINAL RESEARCH Theoretical study of molecular interactions of phosphorus ylide with HF, HCN, and HN 3 Abedien Zabardasti • Ali Kakanejadifard • Motaleb Ghasemian • Mohammad Solimannejad Received: 5 September 2011 / Accepted: 20 December 2011 / Published online: 20 January 2012 Ó Springer Science+Business Media, LLC 2012 Abstract The molecular interactions between phospho- rous ylide (PY) and HX molecules (X = F, CN, and N 3 ) were investigated using the MP2 method at 6-311??G(2d,2p) basis set. Three different patterns including non-classical hydrogen bond HÁÁÁC, XÁÁÁP interaction and classical hydrogen bond HÁÁÁX were found for complex formation between PY and HX molecules. From the predicted models, stability of the HÁÁÁC type complexes are greater than other types. Quantum theories of atoms in molecules and natural bond orbitals methods have been applied to analyze the intermolecular interactions. Good correlations have been found between the interaction energies (SE), the second- order perturbation energy E (2) , and the charge transfer qCT in the studied systems. Keywords Phosphorous ylide Á Non-classical hydrogen bond Á XÁÁÁP interaction Á Hydrogen bond Á Theoretical study Introduction Non-covalent interactions have attracted much attention due to their extensive applications in fields of chemistry, biology, and physics [1]. Hydrogen bond certainly holds the most important position among the intermolecular interactions. It has been demonstrated that the electrostatic interaction, together with induction and dispersion inter- actions, contributes jointly to the formation of hydrogen bond [2]. A large number of theoretical studies on the structure, stability, and vibrational spectra employing ab initio and DFT calculations have been undertaken in recent years for the hydrogen-bonded complexes [3–7]. Ylides as hydrogen bond acceptors (HBA) have been the subject of a number of studies [8–13]. The HB complexes of these specific acceptors can show low-barrier hydrogen bond interactions which are particularly short and strong interac- tions [14]. Despite these preexisting findings, most of these ylides have not been studied as HB acceptor–donors, nor have the changes in their electronic nature when the HB complexes are formed been explored. Therefore, the main focus of this study is to analyze the key structural the HB interactions of phosphorus ylide (PY) molecule with HX (X = F, CN, and N 3 ) which have not been previously studied, and to study how the formation of HB complexes affects the ylide structure. The presence of the partially negative charge on carbon and positive on phosphorus atoms in PY makes it a suitable hydrogen bond acceptor–donor species. In this article, the hydrogen bonding of 1:1 complexes formed between PY and HX molecules have been inves- tigated using second-order Moller–Plesset perturbation (MP2), the large basis sets 6-311??g(2d,2p) has been employed to determine the equilibrium structure and vibrational frequencies of the interacting complexes. Computational methods Calculations were performed using the Gaussian 03 pack- age of codes [15]. The geometries of the isolated ylide, HX Electronic supplementary material The online version of this article (doi:10.1007/s11224-011-9939-0) contains supplementary material, which is available to authorized users. A. Zabardasti (&) Á A. Kakanejadifard Á M. Ghasemian Department of Chemistry, Lorestan University, Khoramabad, Iran e-mail: zabardasti.a@lu.ac.ir M. Solimannejad Quantum Chemistry Group, Department of Chemistry, Faculty of Sciences, Arak University, 38156-8-8349 Arak, Iran 123 Struct Chem (2012) 23:1155–1161 DOI 10.1007/s11224-011-9939-0