Synthesis, structure, spectroscopic, magnetic and electrochemical studies of Ni II phen-dione complex Hassan Hadadzadeh a, * , Marilyn M. Olmstead b , Ali R. Rezvani a , Nasser Safari c , Hamideh Saravani a a Department of Chemistry, Sistan and Baluchestan University, P.O. Box 98135-674, University Street, Zahedan, Iran b Department of Chemistry, University of California, Davis, CA 95616, USA c Department of Chemistry, Shahid Beheshti University, P.O. Box 1983963113, Tehran, Iran Received 31 October 2005; received in revised form 11 February 2006; accepted 14 February 2006 Available online 6 March 2006 Abstract The first crystal structure of Ni II phen-dione complex is reported. This compound is [Ni(bpy) 2 (phen-dione)](PF 6 ) 2 (bpy = 2,2 0 -bipyri- dine and phen-dione = 1,10-phenanthroline-5,6-dione). The complex has been characterized by elemental analysis, IR and electronic absorption spectroscopy and cyclic voltammetry. The electrochemical behavior and electronic spectrum of [Ni(bpy) 2 (phen-dione)](OAc) 2 has also been studied in buffered solutions at pH between 1 and 8. ORTEP drawing of [Ni(bpy) 2 (phen-dione)](PF 6 ) 2 Æ 2CH 3 CN shows that the coordination geometry around the Ni II is a distorted octahedron, with bite angles of 78.1–78.8° for all three bidentate ligands and the two pyridyl rings of the bpy ligands are nearly co-planar, as are the two pyridyl rings of phen-dione. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Ni II complex; Phenanthroline derivatives; Crystal structure; Metal-to-ligand charge-transfer; Cyclic voltammery; Magnetic moment 1. Introduction 1,10-Phenanthroline and its derivatives such as 5,6-di- amino-1,10-phenanthroline, 1,10-phenanthroline-5,6-dione, 2,9-dimethyl-1,10-phenanthroline-5,6-dione and 1,10-phe- nanthroline-5,6-dioxime play important roles as molecular scaffolding for supramolecular assemblies, building block for the synthesis of metallo-dendrimers, thin films of lumi- nescent complexes and ligand for synthesis of ring-opening metathesis polymerization (ROMP) monomer [1–8]. One especially important and desirable class of derivatives are those which retain the twofold symmetry of this ligand and thereby avoid some of the stereochemical problems associated with their tris chelated metal complexes, namely formation of mer and fac isomers. 5,6-Diamino-1,10-phe- nanthroline is particularly important in that it can either directly bridge two metal centers or be condensed with a variety of ortho-quinones to form addition derivatives. For example, the useful bridging ligand, tetrapyrido[3,2- a:2 0 ,3 00 ,2 00 -h:2 000 ,3 000 -j]phenazine, is readily formed upon condensation of phen-diamine with 1,10-phenanthroline- 5,6-dione [3,9]. The focus is on complexes of 1,10-phenanthroline-5,6- dione (Scheme 1) because this ligand has the ability to form stable complexes with a wide variety of metal ions and car- ries an o-quinone moiety with pH-dependent electroactivity [10,11]. Metal complexes of this ligand potentially allow for the variation and control of redox properties over a wide range as well as the fine tuning of potentials through pH changes [12]. Metal complexes of the type [M(LL) 3 ] n+ , where LL is either 1,10-phenanthroline or a modified phen ligand, are particularly attractive species for developing new diagnos- tic and therapeutic agents that can recognize and cleave DNA. The ligands or the metal in these complexes can be varied in an easily controlled manner to facilitate an 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.02.015 * Corresponding author. Tel.: +98 541 242 9602; fax: +98 541 244 6565. E-mail address: hadad@hamoon.usb.ac.ir (H. Hadadzadeh). www.elsevier.com/locate/ica Inorganica Chimica Acta 359 (2006) 2154–2158