Cyanometallate incorporated supramolecular networks based on a nitroalkyl-substituted Cu IIN 4 precursor: Synthesis, crystal structure, thermal and electrochemical studies

Abstract

Two new copper(II) complexes, viz. [Cu(nelin)(H 2O) 2] 2[Fe(CN) 6] · 6H 2O ( 2) and [{Cu(nelin)} 2Ni(CN) 4](ClO 4) 2 · 2H 2O ( 3), have been synthesized using [Cu(nelin)](ClO 4) 2 ( 1) (nelin = 1,9-diamino-5-methyl-5-nitro-3,7-diazanonane) as a nitroalkyl-substituted Cu IIN 4 precursor, and their structures and supramolecular networks have been fully explored using the single crystal X-ray diffraction technique. The H-bonded 1D chains of 2 run along the a-axis, being generated from supramolecular synthons using cations and anions, and are further propagated into a 3D array to form irregular honeycomb-like channels which are divided into two halves, with each half accomodating a helical water chain running in opposite directions to each other. In complex 3, the trinuclear units are arranged in successive rows in a herringbone fashion and bifurcated hydrogen bonding through the uncoordinated terminals of the [Ni(CN) 4] 2− units give rise to a supramolecular (4,4) network. A comparison of the PXRD pattern of complex 2 and its dehydrated form indicate marked changes in the diffraction pattern with the development of a quasi glassy nature in the dehydrated form. The electrochemical properties of 1, 2 and 3 have been investigated in comparative ways using the cyclic voltammetric technique in aqueous and MeCN solutions with Ag/AgCl as a reference electrode. Electrochemical reduction generates the one-electron reduced nitro-radical anion. In water–alcohol glass at 77 K complex 2 exhibits a typical four-line hyperfine EPR spectra with g || = 2.11, g ⊥ = 2.02, A || = 150 Oe and A ⊥ = 5 Oe at ν = 9.45 MHz.