Synthesis and characterization of a new cobalt polymeric spinels

Abstract

Some cobalt spinels were synthesized under hydrothermal conditions, starting from metal chlorides, and Poly N-Acrolylquinazoline. The color properties in these systems mainly depend upon the preparative method and cation distributions, which have been determined by visible and near infrared absorption spectra. We observe the influence of tetrahedral and octahedral preference of cations such as $Co^{2+}$, $Cr^{3+}$, $Mn^{3+}$ upon the formation and the color development of cobalt spinel polymers. All the samples prepared revealed the formation of single spinel with particle size at about 0.8-2.1 $mu m$; $CoAl_2O_4$ reveals kings blue, $CoMn_2O_4$ dark blue and $CoCr_2O_4$ bluish green. Cobalt blues developed giving deep absorption characteristic of tetrahedral $Co^{2+}$ ions at about 550-680 nm; therefore, color changed from kings blue to bluish green in $CoCr_2O_4$, showing the absorption band of octahedral $Cr^{3+}$ ions owing to the large excess octahedral crystal field stabilization energy.