Novel ruthenium(II) and (III) compounds with multidentate Schiff base chelates bearing biologically significant moieties Irvin Noel Booysen ⇑ , Sanam Maikoo, Matthew Piers Akerman, Bheki Xulu School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa article info Article history: Received 13 February 2014 Accepted 11 May 2014 Available online 20 May 2014 Keywords: Ruthenium(II/III) Uracil Chromone Antipyrine Crystal structure abstract In this account, we report the isolation of novel ruthenium(II/III) compounds from the respective reactions of the metal precursor, trans-[RuCl 2 (PPh 3 ) 3 ] with multidentate Schiff base ligands bearing biologically significant moieties (viz. antipyrine, uracil or chromone). From these coordination reactions of trans- [RuCl 2 (PPh 3 ) 3 ] with 4-((pyridine-2yl)methyleneimino)antipyrine (pap), 4-((pyridine-2-ylimino) methylene)-chromone (pch), 2,6-bis-((6-amino-1,3-dimethyluracilimino)methylene)pyridine (H 4 ucp) and 2,6-bis-((antipyrine-imino)methylene)pyridine (bpap); the complex salt, trans-[Ru II Cl(pap)(PPh 3 ) 2 ] BF 4 and the ruthenium(II/III) complexes: trans-P, cis-Cl-[Ru III (pch)Cl 2 (PPh 3 ) 2 ], [Ru II (H 3 ucp)Cl(PPh 3 )] and cis-[Ru II Cl 2 (bpap)(PPh 3 )] were formed, respectively. These ruthenium compounds were characterized via multinuclear NMR, IR, UV–Vis, emission and ESR spectroscopy, conductivity measurements as well as structural elucidations were confirmed via single crystal X-ray diffraction. The redox properties of metallic compounds were investigated by voltammetric analysis. In addition, DFT studies of [Ru II (H 3 ucp)Cl(PPh 3 )] were conducted to provide insight into its intrinsic solid state structural features. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The widespread interest in ruthenium Schiff base compounds is due to their diverse applications rendered through their unique properties such as photoluminescence, catalytic and biological properties [1–5]. Schiff bases are known to stabilize ruthenium in the oxidation states +II and +III which is emphasized by the metal center’s preferential coordination affinity towards neutral nitrogen donor atoms, like imino and pyridyl nitrogens [6,7]. Furthermore, the utilization of multidentate Schiff base ligands provides addi- tional thermodynamic stability through the formation of chelate rings [8]. A typical example is the isolation of the ‘3+3’ paramag- netic ruthenium(III) compounds, [Ru(L R ) 2 ]ClO 4 from the 1:2 molar ratio reactions between [Ru II (DMSO) 4 Cl 2 ] and 4-R-2-((2-(pyridin- 2-yl)hydrazono)methyl)phenol (HL R ; R = H, Cl, Br, Me and OMe) [9]. The discovery of the potent anti-metastatic cancer activity of NAMI A, trans-[RuCl 4 (DMSO)(Im)](ImH) {ImH = imidazole}, has led to concerted efforts in the design of new ruthenium compounds with Schiff base ligands containing various biologically significant moieties [10]. In particular, Schiff bases derived from 4-aminoantipyrine and their ruthenium complexes have shown an array of biological activities including antibacterial and anti-oxidant activities as well as DNA binding capability [11,12]. An example is the organometallic ruthenium(II) complex, [Ru(oap)(CO)(B)Cl] (Hoap = 4-((2-hydroxybenzylidene)imino)- aminoantipyrine) containing the monoanionic O keto N imino O hydroxyl tridentate oap chelator which showed optimal DNA cleavage activ- ity [13]. Recently, we have explored the coordination susceptibility of potentially tridentate Schiff bases (formed from 5,6-diamino- 1,3-dimethyluracil (H 2 ddd) and respective 2-substituted aromatic aldehydes) towards the trans-[Ru II (PPh 3 )] 2+ core [14]. The motiva- tion behind the use of H 2 ddd is its biological relevance as a nucle- otide base derivative as well as the fact that uracil-derivatives are well established chemotherapeutic drugs (e.g. uracil-mustard) [15]. In this account, we report the formation of ruthenium(II/III) compounds with multidentate Schiff bases containing antipyrine, uracil or chromone moieties. The ruthenium compounds, trans- [Ru II Cl(pap)(PPh 3 ) 2 ]BF 4 (1), trans-P, cis-Cl-[Ru III (pch)Cl 2 (PPh 3 ) 2 ] (2), [Ru II (H 3 ucp)Cl(PPh 3 )] (3) and cis-[Ru II Cl 2 (bpap)(PPh 3 )] (4) were isolated from the coordination reactions of trans-[RuCl 2 (PPh 3 ) 3 ] with the Schiff bases: 4-((pyridine-2yl)methyleneimino)antipyrine (pap), 4-((pyridine-2ylimino)methylene)-chromone (pch), 2,6-bis- ((6-amino-1,3-dimethyluracilimino)methylene)pyridine (H 4 ucp) and 2,6-bis-((antipyrine-imino)methylene)pyridine (bpap) ligands, respectively. Our selection of the chromone moiety is based on its biological relevance as a secondary metabolite and that http://dx.doi.org/10.1016/j.poly.2014.05.021 0277-5387/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +27 797378626; fax: +27 332605009. E-mail address: Booyseni@ukzn.ac.za (I.N. Booysen). Polyhedron 79 (2014) 250–257 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly