Structural and DFT Studies on Molecular Structure of Ni(II) Chloride Complex with Pyridoxal Semicarbazone (PLSC). Unusual Coordination Mode of PLSC

Vukadin M. Leovac,^a,* Svetlana Marković,^b Vladimir Divjaković,^a Katalin Mészáros Szécsényi,^a Milan D. Joksović^b and Ivan Leban^c

^a Faculty of Sciences, University of Novi Sad, Trg D.Obradovi}a 4, 21000 Novi Sad, Serbia
^b Faculty of Sciences, University of Kragujevac, R. Domanovi}a 12, 34000 Kragujevac, Serbia
^c Faculty of Chemistry and Chemical Technology, University of Ljubljana, A{ker~eva cesta 5, 1000 Ljubljana, Slovenia
* Corresponding author: E-mail: vule@ih.ns.ac.yu

Abstract
Crystal structure of the NiCl₂ complex with pyridoxal semicarbazone (PLSC), of the empirical formula Ni(PLSC)Cl₂ · 3.5H₂O, gives evidence for an unusual coordination mode of PLSC, observed for the first time. Namely, X-ray analysis of this complex reveales that the elementary cell consists of two monomeric complex cations [Ni(PLSC)(H₂O)₃]²⁺, one centrosymmetric dimeric cation [Ni₂(PLSC)₂(H2O)₄]⁴⁺, eight Cl^- anions, and four molecules of crystal water. In the monomeric cation, PLSC is coordinated in the usual tridentate (ONO) way via the phenolic and carbonyl oxygen atoms and azomethine nitrogen. In contrast, in the dimeric cations, both PLSC molecules, apart from the mentioned ligand atoms, are additionally coordinated via the oxygen of the hydroxymethyl group, but in the role of a bridge, which represents the first example of this coordination mode of PLSC. In both complex cations, Ni(II) is situated in a slightly distorted octahedral environment. The ligand and the complex were additionally characterized by IR spectra and the ligand also by NMR spectra. DFT computation of molecular structure of the complex was carried out at the B3LYP/LANL2DZ level of theory.
Keywords: Nickel(II) complex; pyridoxal semicarbazone; crystal structure; spectroscopy; DFT.