Lutetium arsenate is an inorganic compound of lutetium and the arsenate ion, with the formula LuAsO4. It is a colorless, sparingly soluble crystalline solid and crystallizes in the tetragonal xenotime structure type.
Preparation Lutetium arsenate can be prepared by precipitation from aqueous solutions containing lutetium(III) and arsenate ions. For example, lutetium(III) chloride reacts with sodium arsenate:
LuCl3 + Na3AsO4 → LuAsO4↓ + 3 NaCl
This method has been reported as part of systematic preparations of rare-earth arsenates.
Anhydrous LuAsO4 has also been prepared by heating a mixture of lutetium(III) oxide and arsenic(III) oxide. A sample prepared at the U.S. National Bureau of Standards was heated first at 1050 °C and subsequently at 1250 °C.
Single crystals can be grown by high-temperature flux methods for spectroscopic and structural studies.
Properties Crystal structure Lutetium arsenate crystallizes in the tetragonal crystal system, space group I41/amd (No. 141), with the xenotime or zircon structure type.
The single-crystal refinement gives lattice parameters a = 6.949 Å, c = 6.227 Å with four formula units per unit cell.
An independent powder-diffraction determination at 25 °C gave closely similar parameters of a = 6.9509 Å and c = 6.2321 Å, with a calculated density of 6.924 g/cm3.
The structure contains isolated tetrahedra and eight-coordinate Lu3+ ions. The LuO8 coordination polyhedra share edges to form chains that are linked by arsenate tetrahedra into a three-dimensional framework.
LuAsO4 lies at the small-cation end of the rare-earth arsenate series and is firmly within the xenotime-type stability field.
Solubility Lutetium arsenate is very sparingly soluble in water. A concentration-based solubility-product value of pKsp,c = 22.66 ± 0.01 has been reported.
Vibrational properties Polarized Raman spectroscopy of LuAsO4 single crystals shows the vibrational modes expected for a xenotime-type rare-earth arsenate.
Across the rare-earth arsenate series from Sm to Lu, the internal vibrational frequencies of the AsO4 tetrahedra generally increase with increasing atomic number, while most lattice-mode frequencies change much less strongly.
References