Five-coordinate [(L2)2CuII(X)]z+ (X = H2O, z = 2; X = N3–, SCN–, NO2–, MeCO2–, Cl–, Br– z = 1; L2 = 1-benzyl-[3-(2-pyridyl)]pyrazole) complexes: Structural index, EPR and redox potential correlations

Abstract Mononuclear five-coordinate complexes [(L2)2CuII(X)]z+(ClO4)n (X = H2O, 1, n = z = 2; X = N3– 2, SCN– 3, NO2– 4, MeCO2– 5, Cl– 6, Br– 7 n = z = 1; L2 = 1-benzyl-[3-(2-pyridyl)]pyrazole) have been synthesized and structurally characterized with crystal composition 1, 2, 3•2MeCN, 4•Et2O, 5•3H2O, 6•MeCN and 7•MeCN. The didentate ligand L2 provides a pyridyl and a pyrazole for coordination. Structural index parameter (τ; it assumes a value of 0 and 1 for ideal square pyramidal and trigonal bipyramidal geometry, respectively) for 1–7 are 0.60, 0.01, 0.33, 0.41, 0.26, 0.62, 0.57, respectively. Absorption and EPR spectroscopic, and redox properties of 1–7 have been investigated. Cathodic peak potential (Epc, V vs. saturated calomel electrode, SCE) values in MeCN of 1–7 are 0.08, –0.05, 0.07, 0.05, 0.05, 0.23 and 0.14, respectively. For anion-bound complexes 2, 3, 5–7 useful correlations have been established: (i) Epc (cathodic peak potential of CuII–CuI redox process) vs. structural index parameter τ, (ii) g‖ vs. τ and (iii) Epc vs. g‖ and (iv) A‖ vs. τ. The observed trends have been rationalized.