Molecular structure, spectroscopic properties, NLO and NBO analysis of 3,4-Lutidine and [Ag(3,4-Lutidine) 2 NO 3 ] complex Saied M. Soliman ⇑ Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, 21321 Alexandria, Egypt highlights  The synthesis of silver(I) complex of 3,4-Lutidine (34Lut) is reported.  The molecular geometry of 34Lut and [Ag(34Lut) 2 NO 3 ] are computed.  Their vibrational spectra are assigned using Total Energy Distribution (TED).  Their spectroscopic and electronic properties are compared and discussed.  Nonlinear optical properties of the molecules are predicted. graphical abstract Molecular electrostatic potentials mapped on the electron density surface calculated by DFT method for (a) 3,4-Lutidine (34Lut) and (b) [Ag(34Lut) 2 NO 3 ]. article info Article history: Received 12 April 2013 Received in revised form 30 May 2013 Accepted 31 May 2013 Available online 7 June 2013 Keywords: DFT Silver Lutidine Intramolecular H-bond NLO NBO abstract The molecular structure and electronic properties of 3,4-Lutidine (34Lut) and its silver(I) complex; [Ag(34Lut) 2 NO 3 ] have been reported. The geometry of the titled compounds was optimized using HF and DFT/B3LYP methods. The calculations predicted a distorted tetrahedral coordination geometry around the Ag(I) ion. The complete vibrational assignments of the 34Lut and [Ag(34Lut) 2 NO 3 ] complex have been made on the basis of Total Energy Distribution (TED). The vibrational frequencies calculated using DFT/B3LYP method showed better agreement with the experimental values compared to HF method. For [Ag(34Lut) 2 NO 3 ] complex, the calculations predicted the presence of intramolecular CAHO interactions between the oxygen of the nitrate and the neighboring hydrogen atoms of the coor- dinated 34Lut which is confirmed by the TED analysis of the CAH stretching modes. Unexpected blue shift is predicted for the CAH stretching modes involved in such interactions. A study on the electronic properties, such as HOMO and LUMO energies as well as the molecular electrostatic potential (MEP) was performed using the same level of theory. Natural charges and natural bond orbital (NBO) analyses of the studied molecules were also calculated and interpreted. The dipole moment, linear polarizability and first hyperpolarizability values were used to describe the NLO properties of the studied compounds. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction 3,4-Lutidine (34Lut) is the dimethyl substituted derivative of pyridine. It is also called 3,4-dimethyl pyridine with molecular for- mula C 7 H 9 N. Dimethyl pyridines have been used for synthesis of polymers with thermal and fire resistance properties [1–5]. Also, 0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2013.05.064 ⇑ Tel.: +20 3 5917883; fax: +20 3 5932488. E-mail address: Saied1soliman@yahoo.com Journal of Molecular Structure 1048 (2013) 308–320 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc