ARTICLE DOI: 10.1002/zaac.201100495 Dinuclear Five-Coordinate Copper(II) Complexes with Chelating Diphosphonic Acid Ligands: Hydrothermal Synthesis, Structure, and Thermal Properties Saeed Dehghanpour,* [a] Saeedeh Asadizadeh, [a] and Jalil Assoud [b] Keywords: Diphosphonic acids; Hydrothermal synthesis; X-ray diffraction; Thermal properties; Copper Abstract. The synthesis of two new diphosphonic acid ligands, [ethane-1,2-diylbis(azanediyl)]bis[(4-chlorophenyl)methylene]di- phosphonic acid (L 1 P), [ethane-1,2-diylbis(azanediyl)]bis[(4-bromo- phenyl)methylene]diphosphonic acid (L 2 P), and their corresponding copper complexes, Cu 2 (L 1 P) 2 (1) and Cu 2 (L 2 P) 2 (2) are described herein. Complex 2 was structurally characterized with X-ray single crystal diffraction. The structure of 2 consists of five-coordinate Introduction There has been a growing interest in the synthesis and char- acterization of metal phosphonates due to their potential appli- cations as catalysts, single molecular magnets, sorbents, ion exchangers, protonic conductors, and scale inhibitors. [1–5] In general, metal phosphonates are also reported to form discrete coordination complexes, one-dimensional (1D) chain struc- tures, two-dimensional (2D) layered and three-dimensional (3D) structures. [6–9] One remarkable feature of these com- pounds is that they are capable to form numerous hydrogen bonds, which often contribute to the understanding of the asso- ciated chemistry and mechanism of metal-assisted phosphate ester hydrolysis. [9–11] Much effort has focused on the rational design and controlled synthesis of coordination complexes using phosphonate ligands and factors such as the performance of organic ligand, the metal ion, and the reaction conditions influence the molecular structure and modify properties of metal phosphonates, which are important in practical applica- tions. A variety of (O 3 P-tether-PO 3 ) ligands and numerous metal diphosphonate complexes of type [M n (O 3 P-tether-PO 3 ) m ] were described in recent years. [12–14] Although [O 3 PCH(R)NH(CH 2 ) 2 - NHCH(R)PO 3 ] type ligands also seem to be good candidates for such studies, according to our search, only a few complexes were reported. Fan and co-workers have * Dr. S. Dehghanpour E-Mail: Dehganpour_farasha@yahoo.com [a] Department of Chemistry Alzahra University P.O.Box 1993891176 Tehran, Iran [b] Department of Chemistry University of Waterloo Waterloo, Ontario, Canada N2L 3G1 Z. Anorg. Allg. Chem. 2012, 638, (5), 861–867 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 861 copper(II) ions with a distorted square pyramidal arrangement doubly bridged by OPO from phosphonate groups. The Cu–Cu distance is 4.7810(2) Å. The crystal packing is determined by interdinuclear hy- drogen bonds, which lead to one-dimensional chains. The results of thermogravimetric investigations (TG-DTA), UV/Vis diffuse reflec- tance, infrared and ( 1 H and 13 C) NMR spectroscopy, as well as elemen- tal analyses of compounds 1 and 2 are also presented. reported the structures of the complexes [NH 3 CH(CH 3 )- CH 2 NH 3 ] 2 M 2 [O 3 PCH(Ph)NH(CH 2 ) 2 NHCH(Ph)PO 3 ] 2 · H 2 O, (M = Zn II and Cd II ) and Zn 2 [O 3 PCH(Ph)NH(CH 2 ) 2 NHCH- (Ph)PO 3 ] 2 (HNO 3 ) 2 ·4H 2 O. [15,16] In this work, we present the synthesis, spectral, and elemen- tal analysis of two new diphosphonic acid ligands, [ethane-1,2- diylbis(azanediyl)]bis[(4-chlorophenyl)methylene]diphos- phonic acid (L 1 P), [ethane-1,2-diylbis(azanediyl)]bis[(4-bro- mophenyl)methylene]diphosphonic acid (L 2 P) and their corre- sponding dinuclear copper(II) complexes, Cu 2 (L 1 P) 2 (1) and Cu 2 (L 2 P) 2 (2). These complexes were obtained by hydrother- mal reactions between the phosphonate ligands (L X P) with CuSO 4 in aqueous media by modifying reaction parameters such as the pH, temperature of the reaction mixture, and molar ratio of the starting materials (L X P/Cu 2+ ). Complexes 1 and 2 were characterized by thermogravimetric (TG-DTA), CHN, Energy Dispersive X-ray (EDX) analyses, and UV/Vis diffuse reflectance, IR, and ( 1 H and 13 C) NMR spectroscopy. The structure of 2 was determined by X-ray single crystal diffrac- tion. The spectral properties of these compounds are also dis- cussed. Results and Discussion The formation of diphosphonic acid ligands takes place in two steps (Scheme 1). The first step in this process involves the formation of a diimine ligand (L x ) by the reaction of ethyl- enediamine with benzaldehyde derivatives. In the second step, trimethyl phosphite reacts with diimine ligand to afford the diphosphonic acid ligand (L X P). The ligands were insoluble in water and common organic solvents such as MeOH, EtOH, MeCN, THF, DMSO, and DMF, but soluble in aqueous alkali solution.