Tetracyanidopalladates of Cu(II) with 2-aminoethylpyridines as blocking ligands: The role of the 2-aminoethyl arm position on the pyridine ring

Three novel Cu(II) compounds Cu(2aepy)Pd(CN)4 (1), Cu(3aepy)Pd(CN)4H2O (2) and [Cu(4aepy)2(H2O)2][Pd(CN)4] (3) (Xaepy = X(2-aminoethylpyridine), X = 2,3,4) were isolated in single crystal form from the aqueous systems Cu2+ – Xaepy – [Pd(CN)4]2–. The resulting crystal structures depend on the position of 2-aminoethyl arm on the pyridine ring: 1 exhibits a three-dimensional (3d) polymeric structure and only one chelating 2aepy ligand is ligated to the pentacoordinated Cu(II) atom (τ = 50%); the crystal structure of 2 features a puckered 2d polymer formed by hexacoordinated Cu(II) atoms (4 + 1 + 1 form) and [Pd(CN)4]2– anions linked by bridging cyanido ligands; and the Cu(II) atoms are additionally bridged by 3aepy ligands. The crystal structure of 3 is built up of positively charged chains in which [Cu(H2O)2]2+ fragments are linked by a pair of 4aepy ligands, giving hexacoordinated Cu(II) in the 4 + 2 form, with [Pd(CN)4]2– counter anions. Hydrogen bonds reinforce the crystal structures of 1–3. Variable temperature magnetic studies based on susceptibility and magnetization measurements down to 2 K reveal that 1 deviates from Curie–Weiss behavior at low temperature, while 2 and 3 exhibit Curie–Weiss behavior with θ values of −0.85 K and −0.46 K for 2 and 3, respectively.