Generation of paramagnetic centers in carboxylatedmaterials via coordination attachment of diamagnetictetraazamacrocyclic complexes of nickel(II)

Abstract

Coordination bonding of Ni(II) tetraazamacrocyclic (TAMC) complexes to car-boxylic groups of organic polymers and graphene oxide paper (GOP) is pro-posed for a facile generation of paramagnetic centers by combining twodiamagnetic components. The coordination functionalization occurs under basicconditions in water solution at room temperature. The coordination configura-tion of central Ni(II) changes from tetracoordinated square-planar to hexaco-ordinated pseudooctahedral, which implies the conversion from low-spin tohigh-spin nickel centers. In the case of organic polymers, the coordinationbonding of Ni(II) macrocycles gives rise to characteristic changes in coloration(from yellow-orange to violet-blue), as well as clearly manifests itself in UV–visible, FTIR and EPR spectra. In the case of GOP, in addition to evident changesin FTIR spectra, morphological alterations in the mat surface and an increase inthe mat thickness are observed in SEM images, which can be explained by anintercalating effect of voluminous macrocyclic cations, as well as by partialdisintegration of GOP structure due to the liquid-phase treatment. The effectivemagnetic moments of tetraazamacrocycles attached to organic polymers varyfrom 0.88 to 1.47 BM, whereas for GOP considerably higher values of 2.10 and 2.87 BM were obtained.