Environment of Cobalt(II) in Nitrate Glass

Electronic Spectra and Stability of Cobalt Halide Complexes in Molten Calcium Nitrate Tetrahydrate

“…Tananaev and Dzhurinskii [3,4] ascribed the changes in cobalt(II) absorption spectra in lithium nitratepotassium nitrate eutectics to successive cobalt(II) halide complex formation and to the change in Co(II) co-ordination from octahedral in pure nitrate to tetrahedral in halide containing melts. Later, on the basis of X-ray diffraction measurements [5], the spectrum of Co(II) in pure nitrate melts was attributed to dodecahedral [Co(NO 3 ) 4 ] 2− species [6]. Analogous spectral changes were observed upon addition of chloride into cobalt(II) solution in molten ammonium nitrate [7].…”

“…The coordination number of cobalt(II) and the structure of its complexes often depend on the ligand used [1]. The wellknown octahedral -tetrahedral equilibria in aqueous solutions is best illustrated by addition of concentrated hydrochloric acid to aqueous cobalt(II) salt, when the pale red octahedral [Co(H 2 O) 6 ] 2+ is changing to intense blue tetrahedral [CoCl 4 ] 2− [2]. Similar changes in co-ordination occur when chloride or bromide is added to cobalt(II) solution in nitrate melts.…”

The structural role and coordination environment of cobalt in 45P2O5–CaO–Na2O phosphate glasses: thermal properties and Raman, UV–vis-NIR, and EPR spectroscopy

“…24,25,[32][33][34] These materials have been characterised by various methods such as XRD, SEM, DSC, density, EDS, EXAFS, XANES, diffuse reflectance, UV-vis-IR absorption, Raman, luminescence, EPR, solid state NMR spectroscopy, and DC and AC conductivity analyses. [17][18][19][20][21][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Particularly, optical spectroscopy has been extensively used for structural analysis, since the colour provided by Co 2+ is related to its coordination number. 36,38 The latter varies as a function of optical basicity, a concept that is useful to explain the electron density distribution in glass networks.…”

“…[17][18][19][20][21][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Particularly, optical spectroscopy has been extensively used for structural analysis, since the colour provided by Co 2+ is related to its coordination number. 36,38 The latter varies as a function of optical basicity, a concept that is useful to explain the electron density distribution in glass networks. 31,39 Co 2+ in octahedral coordination exhibits a pink colour in contrast to its tetrahedral counterpart, which is blue with a substantially higher extinction coefficient.…”

“…38 Other less common intermediate Co species with 5-fold 22,27,30 and 8-fold coordination 32 have been reported. Despite the fact that the relationship between the optical basicity and coordination number of Co 2+ has been known for a long time, [35][36][37][38][39] most of the studies on glasses have varied both the basicity of the glass network and the CoO content simultaneously. Thus, the variation of more than one parameter at a time has led to biased correlations, such as the ratio of tetrahedral coordination being necessarily proportional to the CoO content.…”