Synthesis, characterization, crystal structure, electrochemical properties and electrocatalytic activity of an unexpected nickel(II) Schiff base complex derived from bis(acetylacetonato)nickel(II), acetone and ethylenediamine Manawadevi Y. Udugala-Ganehenege • Yuping Liu • Craig Forsyth • Alan M. Bond • Jie Zhang Received: 21 May 2014 / Accepted: 6 August 2014 Ó Springer International Publishing Switzerland 2014 Abstract The synthesis, crystal structure and electro- chemical properties of a Ni(II) Schiff base complex, [Ni(L)]PF 6 (where L is 2,4,9,11,11-pentamethyl-2,3,4 tri- aza-1-one-4-amine) are reported herein. The complex has been characterized by its electrochemical behavior, X-ray crystallographic structural analysis, physio-chemical methods and spectroscopic techniques. Electrospray mass spectroscopic analysis gives a dominant ion peak with m/ z = 296 which corresponds to the {[Ni(L)]PF 6 –HPF 6 } ? fragment. Cyclic voltammograms for [Ni(L)]PF 6 , obtained in DMF (0.1 M Bu 4 NPF 6 ) at a glassy carbon electrode with a scan rate of 100 mV s -1 , exhibit reversible ([Ni II (L)] ? / [Ni I (L)]) reduction and chemically irreversible ([Ni II (L)] ? / [Ni III (L)] 2? ? electroactive product) oxidation processes at -2.05 and 0.62 V, respectively. The diffusion coefficient, calculated using the Randles–Sevcik relationship, is 9.7 9 10 -6 cm 2 s -1 . Electrochemical studies reveal that the Ni I reduced form of the complex is capable of cata- lyzing CO 2 reduction at a potential that is thermodynami- cally more favorable than for the reduced [Ni(N,N 0 - ethylenebis(acetylacetoneiminato)]complex. Spectroelect- rochemical analyses following bulk electrolysis of [Ni(L)]PF 6 under CO 2 revealed the formation of oxalate and bicarbonate. Introduction The synthesis of transition metal complexes of cyclic and hemicyclic Schiff base ligands has received significant attention over several decades, due to their applications in areas such as catalysis, bioinorganic chemistry and coor- dination chemistry [1–6]. Their chemical and biological properties are very sensitive to structural variations, so that complexes with a variety of ligand structures are of par- ticular interest [7]. Due to their exceptionally high ther- modynamical stability and structural simplicity, these complexes are very useful as model systems to study complicated biological systems such as metalloproteins [3– 5]. More than 139 nickel(II) complexes, containing the 1,4,8,11-tetraazacyclotetradecane backbone, are found in the Cambridge structural database, and among them, many complexes electrocatalytically reduce CO 2 [8]. Metal template synthesis has been employed for the synthesis of most of these macrocyclic complexes, because it often provides selective routes toward expected products that are not obtained in the absence of metal ions. However, pro- ducts isolated from the template reaction mixtures some- times show completely unpredictable structures [9], as observed for the complex reported herein. Such observa- tions encourage the investigation of novel synthetic path- ways to synthesize macromolecules with different structural backbones. In this study, many attempts made to synthesize the cyclic 5,7,12,14-tetramethyl-1,4,8,11-tetra- azacyclotetradeca-1,4,7,11-dinickel(II) complex, by fol- lowing the traditional template synthetic procedure, ulti- mately resulted in the unexpected preparation of a novel hemicyclic Schiff base complex, [Ni(L)]PF 6 . This implies that the thermodynamic stability of the hemicyclic Schiff base complex is higher than that of its cyclic analog. The present paper therefore reports the synthesis, electrospray Electronic supplementary material The online version of this article (doi:10.1007/s11243-014-9872-3) contains supplementary material, which is available to authorized users. M. Y. Udugala-Ganehenege (&) Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka e-mail: myug@pdn.ac.lk; mdechem@yahoo.com Y. Liu  C. Forsyth  A. M. Bond  J. Zhang School of Chemistry, Monash University, Clayton, VIC 3800, Australia 123 Transition Met Chem DOI 10.1007/s11243-014-9872-3