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

The complexes [(L2)2CuII(X)]z+(ClO4)n (X = H2O, n = z = 2; X = N3−, SCN−, NO2−, MeCO2−, Cl−, Br− n = z = 1) have been synthesized and structurally characterized. For anion-bound five-coordinate complexes, useful linear correlations have been established: (i) Epc (cathodic peak potential of CuII–CuI redox process) vs. structural index parameter τ, (ii) g||vs. τ, (iii) Epcvs. g|| and (iv) A‖vs. τ. [Display omitted] •The complexes [(L2)2CuII(X)]z+(ClO4)n (X = H2O, z = 2; X = N3−, SCN−, NO2−, MeCO2−, Cl−, Br− z = 1).•Variation of Structural index parameter τ.•Linear correlations: Epcvs. τ, g‖vs. τ, A‖ vs. τ and Epcvs. g‖.•Epc vs. τ plot: first report for five-coordinate anion-bound copper(II) complexes. 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 bidentate 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 1–3, 5–7 are 0.60, 0.01, 0.33, 0.26, 0.62, 0.57, respectively. Absorption and EPR spectroscopic, and redox (except for 1) properties of 1–7 have been investigated. Cathodic peak potential (Epc, V vs. saturated calomel electrode, SCE) values in MeCN of 2–7 are −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 (CuII–CuI redox process) vs. structural index parameter τ, (ii) g‖vs. τ, (iii) A‖vs. τ and (iv) Epcvs. g‖. The observed trends have been rationalized.