%0 Journal Article
%T The N HF Interactions in the X-Pyridazine Complexes: Substituent Effects and Energy Components
%A Ali Ebrahimi
%A Mostafa Habibi-Khorassani
%A Farideh Badichi Akher
%A Abdolkarim Farrokhzadeh
%J Advances in Physical Chemistry
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/362608
%X The effects of substituents on the NˋHF interactions in the X-pyridazine (X = N(CH3)2, NHCH3, NH2, C2H5, CH3, OCH3, OH, CN, OF, NO2, F, Br, Cl, and ) complexes have been studied at the B3LYP/6-311++G(d,p) level of theory. In all complexes, the binding energies increase for the electron-donating substituents and decrease for the electron-withdrawing substituents. A negative cooperativity is observed for two hydrogen bond interactions. There are meaningful relationships between the Hammett constants and the energy data and the results of population analysis in the binary and ternary complexes. Symmetryadapted perturbation theory (SAPT) analysis was also carried out to unveil the nature of hydrogen bond in the complexes 2 and 3. The electron-donating substituents increase the magnitude of the SAPT interaction energy components and the electron-withdrawing substituents decrease those components. The highest/lowest change is observed for the component. The effect of C2H5 (or CH3) on different components is higher than OCH3 in the complex 2 while the trend is reversed in the complex 3. It is demonstrated that the electrostatic interaction plays a main role in the interaction, although induction and dispersion interactions are also important. 1. Introduction The diazine rings are building blocks of many important natural and synthetic compounds [1]. They have been the subject of extensive research, particularly in the pharmaceutical and agrochemical areas due to their broad activities, such as antihypertensive and anti-inflammatory activity [2每5]. The hydrogen bond plays a crucial role in biology, chemistry and related disciplines [6每13]. Cooperativity is an important characteristic of hydrogen bond interactions. The role of hydrogen bond may be modified by the cooperativity of hydrogen bonds in many chemical and biological systems [14每16]. It plays an important role in controlling and regulating the processes occurring in living organisms. Many physical and chemical properties of materials are determined by hydrogen-bonding cooperativity [17每20]. For example, the hydrogen bond cooperativity is relevant for sustaining the stable conformers of biological molecules [21, 22] and constructing the crystal structures [22, 23]. The effects of substituents on the binding energies of the X-pyridazine (HF)n ( ) complexes (represented by 1每3 in Scheme 1) and the cooperativity of the H-bond interactions have been investigated in the present study. Substituent X is located at position 4 of pyridazine ring, which is meta relative to N2 in 1 and 2 and para relative to N1 in
%U http://www.hindawi.com/journals/apc/2012/362608/