Developments in Ceramic Materials Research

In: Developments in Ceramic Materials Research ISBN 978-1-60021-770-8
Editor: Dena Rosslere, pp. 97-140 © 2007 Nova Science Publishers, Inc.
Chapter 4
SYNTHESIS, SPECTROSCOPIC AND MAGNETIC
STUDIES OF THE M(PO3)3 (M III = TRANSITION
METAL IONS) METAPHOSPHATES
José M. Rojo, José L. Mesa and Teófilo Rojo ∗
Dpto. de Química Inorgánica, F. Ciencia y Tecnología,
Universidad del País Vasco/EHU,
Apdo. 644, E-48080 Bilbao, Spain
ABSTRACT
The solid state chemistry of polyphosphates in which the transition metal exhibits a
trivalent oxidation state is traditionally considered unusual. The great ability of the
phosphate frameworks to stabilize this oxidation state is produced for the relatively high
charge in (PO4) 3- tetrahedra that favors the formation of anionic frameworks with high
degree of mechanical, chemical, and thermal stability. The literature about this kind of
compounds shows the existence of several polymorphic forms of these phases which
crystal structure has been solved. Unfortunately, even if good crystals for X-ray structure
determination were obtained, pure phases had not been prepared. This fact has precluded
carrying out any study on the physical properties of these materials. A method based on
the control of M/P ratio in the reaction medium has allowed us the synthesis of pure
phases. On this basis, the M(PO3)3 metaphosphates (M III = Ti, V, Cr, Mo and Fe) have
been synthesized starting from a mixture of the metallic oxides and (NH4)2HPO4, with
different M:P ratios by using the ceramic method.
These phases exhibit a crystal structure constructed from (MO6) octahedra linked
through infinite (PO3)∞ chains of (PO4) tetrahedra to give rise to compact threedimensional
crystal structures. The IR spectra of these phases show the characteristic
bands of the methaphosphates with ring or chain structure. The absorption electronic
spectroscopy recordered by the diffuse reflectance method shows the presence of the spin
allowed transitions, being calculated the values of the splitting parameter of the
crystalline field (Dq), as well as, these ones of the Racah parameters (B and C). The ESR
spectra of these compounds exhibit isotropic signals, centered at values of the g-
∗ Corresponding author: e-mail: teo.rojo@.ehu.es; Phone: +34-946012458; Fax: +34-946013500 (T. Rojo)