Synthesis and characterization of copper(I) coordination compounds with (1-(2-pyridylazo)-2-naphthol) and (4-(2-pyridylazo)resorcinol) M. Płotek a,c , R. Starosta b , W. Nitek a , U.K. Komarnicka b , G. Stochel a , A. Kyzioł a,⇑ a Faculty of Chemistry, Jagiellonian University in Krakow, Ingardena 3, 30-060 Krakow, Poland b Faculty of Chemistry, University of Wroclaw, Joliot-Curie 14, 50-383 Wroclaw, Poland c Interacademy Institute of Conservation and Restoration of Works of Art, Jan Matejko Academy of Fine Arts in Krakow, Lea 27-29, 30-052 Krakow, Poland article info Article history: Received 16 September 2013 Accepted 1 November 2013 Available online 19 November 2013 Keyword: Copper(I) complexes 1-(2-Pyridylazo)-2-naphthol 4-(2-pyridylazo)resorcinol DFT studies Structural studies abstract Two cuprous complexes with 1-(2-pyridylazo)-2-naphthol (PAN) or 4-(2-pyridylazo)resorcinol (PAR) and triphenylphosphines, [Cu(PAN)(PPh 3 ) 2 ]BF 4 (1) and [Cu(PAR)(PPh 3 ) 2 ]BF 4 (2), are described in this work. The structures of both compounds were characterized by NMR and UV–Vis spectroscopies, mass spec- trometry, IR-ATR measurements and DFT calculations. The single crystal diffraction of both complexes confirmed that the coordination polyhedrons around the copper centres are distorted tetrahedrons. Inter- estingly, the PAR and the PAN ligands are not planar in the synthesized complexes. The ligands coordinate to the central copper(I) ions by only two nitrogen atoms: one from pyridine and one from an azo group. The oxygen atoms from the hydroxyl groups do not form bonds with copper, but take part in strong intra- molecular hydrogen bonds, which stabilize the conformations of the ligands. It is noteworthy that these bonds have different characters. In complex 2 we observed a typical O–HÁÁÁN hydrogen bond, whereas in complex 1 proton transfer takes place, resulting in OÁÁÁH–N bond formation. DFT data confirm the differ- ent characters of the H-bonds observed in the X-ray structures. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In this article we present the synthesis pathways, physicochem- ical analysis and crystal structures of two copper(I) complexes: [Cu(PAN)(PPh 3 ) 2 ]BF 4 (1) and [Cu(PAR)(PPh 3 ) 2 ]BF 4 (2). Our interest in copper and its complexes is due to the fact that this metal is an essential element, necessary for the proper functioning of the human body. Its confirmed antibacterial, antifungal, antiviral, anti-inflammatory and anticancer activity makes copper com- pounds attractive and raises hopes that powerful therapeutic agents can be discovered among them [1–5]. 1-(2-Pyridylazo)-2-naphthol (PAN) and 4-(2-pyridylazo)resor- cinol (PAR) (Scheme 1) are popular ligands applied in chelatomet- ric and spectrophotometric analysis, due to their ability to coordinate to many different metals, with the formation of colored complexes [6–9]. PAR and PAN are bidentate or tridentate chelat- ing ligands. If they are bidentate, they can be bonded with metal ions by the N1 and N3 atoms, whereas if they are tridentate, by the N1, N3 and O8 atoms (Scheme 1). Generally, the anticancer activity of copper compounds results from their ability to catalyze reactive oxygen species production [2,3]. Additionally, for complexes in which the copper(I) ion is coordinated to a ligand possessing a phenanthroline skeleton, nuclease activity has been proved [10,11]. Moreover, the azo group, N@N, also arouses the interest of researchers who are fo- cused on the synthesis of potential chemotherapeutic agents, since a high cytotoxic effect was observed for ruthenium(II) complexes possessing phenylazopyridine skeleton ligands. The mentioned complexes oxidize glutathione (GSH) to glutathione disulfide (GSSG) and as a result inhibit GSH activity as a reducer of reactive oxygen species [12]. Furthermore, Romero-Canelon et al. have re- cently presented ruthenium and osmium areneazo- and imino- pyridine complexes as very potent and selective toward cancer cells. It was demonstrated that these complexes possess a high selectivity for membrane binding, their activity is not dependent on p53, they are not cross-resistant to platinum drugs, and finally they induce a high incidence of late stage of apoptosis [13]. Generally, copper complexes offer several advantages over ruthenium and platinum compounds, including amongst others: reduced toxicity and the possibility of controlling the shape as well as chemical and pharmacological properties of the complex by the adequate selection of the ligands. Presented in this paper are two copper(I) complexes that contain two basic building blocks: a bio- logically active metal center (i.e. a copper ion) and a bidentate li- gand (i.e. PAN and PAR ligands). In detail, the combination of copper(I) properties for reactive oxygen species production to- gether with the tendency of phenylazopiridine skeleton ligands for GSH deactivation could lead to powerful drugs being obtained. 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.11.004 ⇑ Corresponding author. Tel.: +48 126632221. E-mail address: kyziol@chemia.uj.edu.pl (A. Kyzioł). Polyhedron 68 (2014) 357–364 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly