Second-sphere ligand-field effects in solid solutions of anhydrous transition-metal phosphates.
Powders of the solid solutions In1-xCrxPO4 (0 < or = x < or = 1), In1-xCrx(PO3)3 (0 < or = x < or = 1), (In1-xCrx)4(P2O7)3 (0 < or = x < or = 0.7), and In1-xMnx(PO3)3 (0 < or = x < or = 0.8) have been synthesized by solid-state reactions. Depending on the dopant concentration, these materials show striking variations in color [In1-xCrxPO4, light pink to green-brown; (In1-xCrx)4(P2O7)3, light pink to red-brown; In1-xCrx(PO3)3, pale green to green; In1-xMnx(PO3)3, light blue to purple). Powder reflectance spectra of the solid solutions were measured in the UV/vis/NIR region (5500-35000 cm(-1)). Observed d-d electronic transition energies and results of calculations within the framework of the angular overlap model (AOM) for the low-symmetry chromophores [M(III)O6] (M = Cr, Mn) are in good agreement. In the case of the mixed In/Cr phosphates, the observed color changes can be related to second-sphere ligand-field effects. Clear evidence for differences in the pi-bonding of oxygen toward Cr(3+) (d(3) ion) and In(3+) (d(10) ion) are observed. For In1-xMnx(PO3)3, the variation in color is attributed to a slightly increasing elongation of the [Mn(III)O6] chromophore with increasing dopant concentration.
Thauern
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Department of Inorganic Chemistry, University of Bonn, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany.
Glaum
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