Cu(II) complexes of cyclotriphosphazene bearing Schiff bases: Synthesis, structural characterization, DFT calculations, absorbance and thermal properties Semih Dog ˘an, Ceylan Mutlu Balcı, Ahmet S ßenocak, Serap Bes ßli ⇑ Department of Chemistry, Gebze Technical University, Gebze, Kocaeli, Turkey article info Article history: Received 9 January 2020 Accepted 28 March 2020 Available online 3 April 2020 Keywords: Copper complexes Schiff bases Cyclophosphazenes UV–Vis absorption Thermal analysis abstract N 3 P 3 [(2,2 0 -biphenoxy) 2 (OC 6 H 4 N = CH-C 6 H 4 F) 2 ](L1) and N 3 P 3 [2,2 0 -biphenoxy(OC 6 H 4 N = CH-C 6 H 4 F) 4 ](L2), which are cyclotriphosphazene derivatives containing biphenyl-2,2 0 -dioxy group(s) and Schiff base moi- eties, were synthesized. The structures of L1 and L2 were characterized by elemental analysis, FT-IR spec- troscopy, MALDI-TOF mass spectrometry, 1 H and 31 P NMR spectroscopy. Moreover, the molecular structure of L2 was unambiguously determined by X-ray crystallography. C1 and C2 were prepared from the complexation reactions of L1 and L2 with CuCl 2 salts. The characterization of these complexes was carried out using various methods (elemental analysis, FT-IR spectroscopy, MALDI-TOF mass spectrom- etry). UV–Vis experiments, including titration and continuous variation (Job’s plot analysis), proved that all of the spectrophotometric properties in the solution state support the binding mode of L-Cu 2+ of the complexes C1 and C2. Theoretical DFT calculations were carried out to confirm the molecular geometry and the binding type of the Cu(II) complexes C1 and C2. The analyses revealed that the metal ion in the two novel mononuclear and dinuclear Cu(II) complexes (C1 and C2) coordinate to two imine groups of geminal Schiff bases in the ƞ 2 -geminal-N 2 coordination mode. The magnetic properties of C1 and C2 were analysed with VSM and ESR techniques. Furthermore, the thermal properties of L1, L2, C1 and C2 were investigated and the results were compared and discussed. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction Schiff bases are considered as ‘‘exclusive ligands” because they can coordinate to different metals and have a rich coordination chemistry [1–13]. Different novel molecular complexes are inter- esting because of the nature of molecular interactions and their contributions to the molecular surface [14–19]. Copper(II) com- plexes constitute an important class in chemistry, not only for their interesting coordination chemistry, but also for their geometry and oxidation state [1–6,20]. Therefore, the design and construction of novel copper metal complexes with Schiff bases have attracted great interest due to their attractive properties, simple synthesis, stability, low toxicity, good biocompatibility [21,22] and their potential applications in magnetism, catalytic activity, anticorro- sion utilization, bioinorganic properties and antimicrobial, antifun- gal and anticancer activities [5–9,11–13,23–26]. Hexachlorocyclotriphosphazene, which has a stable PAN skele- ton and six active P-Cl bonds, can be easily modified by a nucle- ophilic substitution reaction with desired groups, such as a Schiff base, on the phosphorous atoms. Hence, they provide a wide vari- ety of multimodal ligand systems [27–36]. In recent years, some works have been reported regarding the synthesis of multi-site coordination ligand systems consisting of Schiff bases and hex- achlorocyclophosphazene [34–38]. When these type ligand sys- tems are reacted with appropriate metal salts, a huge structural variety of metal complexes can be created [28,30,34,35]. In addi- tion, one of the important advantages of the cyclotriphosphazene core is optical inertness, which means that the optical properties of cyclotriphosphazene derivatives can be modified in the UV–Vis region [39,40]. In the present study, new cyclophosphazene ligand systems (L1 and L2) containing Schiff bases were synthesised. Firstly, two 2,2 0 - biphenyl groups (1) and one 2,2 0 -biphenyl group (2) were substi- tuted on the cyclotriphosphazene cores in spiro positions in order to bond to two and four Schiff bases groups, which could then undergo reactions with copper ions. Next, the two and four Schiff bases were substituted on the cyclotriphosphazene cores in the https://doi.org/10.1016/j.poly.2020.114541 0277-5387/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Chemistry, Gebze Technical University, Gebze, Kocaeli, Turkey E-mail address: besli@gtu.edu.tr (S. Bes ßli). Polyhedron 183 (2020) 114541 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly