Rare-Earth Tetracyanidoborate Salts - Structural Features and Properties Including Luminescence of [RE­(H2O)8][B(CN)4]3·nH2O and [RE­(H2O)7{[kappa]1N-B(CN)4}][B(CN)4]2 (RE = Y, Tb, Dy, Ho, Er, Tm, Yb, Lu; n < or = 3)

New tetracyanidoborate salts with hydrated rare-earth-metal cations (RE3+) were synthesized by the reactions of rare-earth-metal oxides or hydroxides with tetracyanidoboronic acid, H[B(CN)4]·nH2O. Two groups of isostructural compounds were obtained with the formulas [RE(H2O)8][B(CN)4]3·nH2O (structure I) and [RE(H2O)7{[kappa]1N-B(CN)4}][B(CN)4]2 (structure II) for RE = Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu and n ≤ 3. Both structures have discrete eight-coordinate RE3+ complex cations, as [RE(H2O)8]3+ in structure I and [RE(H2O)7{[kappa]1N-B(CN)4}]2+ in structure II. The heating of the compounds to temperature of ca. 160 °C gives anhydrous samples, but elongated heating to temperatures above ca. 200 °C leads to the slow decomposition of the tetracyanidoborates. The luminescence properties of a solid sample of the anhydrous Tb salt and a solution of the Dy salt were investigated. Both show intense lines in their excitation and emission spectra that were assigned to electronic transitions within the f and d shells.