SPECTROSCOPIC AND MAGNETIC-PROPERTIES OF 3 M(PO3)(3) (M = CR AND MO) METAPHOSPHATES

Three metaphosphates with formula M(PO3)(3) (M = Cr and Mo) and Cr-2(P 6O18) have been synthesized and characterized. IR data allow establish ment of a good correlation between the vibrational frequencies and the chain or ring structures of the M(PO3)(3) (M = Cr, Mo) metaphosphates and the Cr-2(P6O18) hexametaphosphate, respectively. The reflectance diffuse spectra show bands belonging to the Cr-III and Mo-III cations in octahedral symmetry. The values of 10Dq and Racah parameters B and C have been calculated. The percentage of reduction calculated for the B parameter (approximate to 70%) is indicative of a significant degre e of covalence in the M-O (M = Cr, Mo) bonds. The EPR spectra of the m etaphosphate compounds have been explained on the basis of the existen ce of more than one different environment for the metallic cations. In doped aluminium metaphosphates with Cr-III and Mo-III ions the EPR da ta indicate the presence of one centre with \D\ > hv and two centres w ith \D\ < hv. Magnetic measurements show an antiferromagnetic behaviou r for all compounds. In the case of the Cr-2(P6O18) hexametaphosphate the existence of a weak ferromagnetism intrinsic to the sample has bee n observed at ca. 3 K.