DFT studies of structural and some spectral parameters of copper(II) complexes with N,N,N 0 ,N 00 -tetrakis (2-hydroxyethyl/propyl) ethylenediamine and tris(2-hydroxyethyl)amine Rakesh Kumar a , Sangeeta Obrai a,⇑ , Joyee Mitra b , Aparna Sharma a a Department of Chemistry, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar 144 011, Punjab, India b Department of Chemistry, University of Illinois at Urbana-Champaign, Matthews Ave., Urbana, IL 61801, United States highlights  Primary coordination sphere of copper(II) complexes are optimized.  A comparison of crystallography with optimized DFT data is carried out.  Vibrational bands of optimized structures are assigned and compared with experimental data.  Energy gaps of frontier orbital (HOMO–LUMO) have been calculated.  Optimized structures are in excellent qualitative agreement with crystal data and spectroscopic data. graphical abstract article info Article history: Received 8 May 2013 Received in revised form 25 May 2013 Accepted 4 June 2013 Available online 20 June 2013 Keywords: DFT Copper(II) complexes Structural parameters Tetrapodal Tripodal ligands abstract The structures and some spectral parameters of three copper(II) complexes; [Cu(THEEN)(H 2 O)](PIC) 2 (1), [Cu(THPEN)] (PIC) 2 C 3 H 8 O(2) and [Cu(TEAH 3 )(PIC)] (PIC)(H 2 O) (3), previously synthesized and characterized by X-ray diffraction, are here computationally studied by using density functional theory (DFT) in its hybrid form B3LYP. In these complexes, THEEN is N,N,N 0 ,N 00 -tetrakis(2-hydroxyethyl) ethy- lenediamine and THPEN is N,N,N 0 ,N 00 -tetrakis(2-hydroxypropyl) ethylenediamine, tetrapodal ligands and TEAH 3 is tris(2-hydroxyethyl)amine, a tripodal ligand. The primary coordination sphere of copper(II) ion in complexes (1), (2) and (3) are optimized, structural parameters are calculated, vibrational bands are assigned and energy gaps of frontier orbital (HOMO–LUMO) have been calculated with B3LYP/6- 31G/LANL2DZ level of theory using DMSO as solvent. The calculated geometric and spectral results reproduced the experimental data with well agreement. Theoretical calculated molecular orbitals (HOMO–LUMO) and their energies have been calculated that suggest charge transfer occurs within the complexes. Ó 2013 Elsevier B.V. All rights reserved. Introduction Density functional theory in its hybrid form B3LYP is the most accurate and efficient computational method for the quantum chemical modeling of coordination compounds including those of biological relevance [1,2]. The spectroscopic properties and reactivities of transition metal compounds can also be more effi- ciently computed and reliably interpreted with DFT than ab intio and semi-empirical quantum-chemical method. These computa- tions are often based on known structural data [3]. Reliable predic- tion of spin state energies is a well known problem for quantum mechanical approaches in general and DFT in particular. Although no model is perfect including B3LYP and the quest for better model continues [4–7]. 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.06.021 ⇑ Corresponding author. Tel.: +91 9814245310; fax: +91 181 2690320. E-mail address: o.sangeeta@yahoo.com (S. Obrai). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 244–249 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa