Photoluminescent chromium molybdate cluster coordinated with rare earth cations: synthesis, structure, optical and magnetic properties

The Anderson-Evans cluster, {CrMo6O24}(n-), exhibits ruby-like red emission. During our attempts to engineer new photoluminescent crystals using chromium molybdate as a molecular building block, we isolated four new rare-earth based chromium molybdates: [Gd(H2O)(7){CrMo6(OH)(6)O-18}]center dot 4H(2)O, 1, (4-pycH)[Gd(H2O)(4){CrMo6(OH)(6)O-18}(4-pycH)]center dot 5H(2)O, 3, and (4-pycH)(2)[Ln(H2O)(6){CrMo6(OH)(6)O-18}]center dot 2H(2)O, (Ln = Tb, 4 and Sm, 5; H4-pyc = 4-pyridine carboxylic acid and 4-pycH = 4-pyridinium carboxylate). All are nonmolecular solids characterized by extended 1-D or 2-D interactions between rare-earth ions and the chromium molybdate cluster. All solids showed intense room-temperature Cr3+ related red emission and also exhibited weak antiferromagnetism at low temperatures.