New tetracyanidoborate salts with hydrated rare‐earth metal cations (RE3+) were obtained by the reaction of rare‐earth metal oxides or hydroxides with tetracyanidoboronic acid. A group of isostructural compounds was obtained, which has the chemical formula [RE{B(CN)4}3(H2O)5]·nH2O (RE = La, Ce, Pr, Nd, Sm, Eu, and Gd; n ≤ 0.5). In all compounds the rare‐earth metal cations have the coordination number nine with a RE‐O5N4 environment. They are connected to chains through one bridging tetracyanidoborate anion per RE3+ cation, according to [RE{μ‐B(CN)4}{κN‐B(CN)4}2(H2O)5]·nH2O. Solid samples of the Eu salt show luminescence with intense lines in the excitation and emission spectra caused by electronic transitions within the f and d shells.Thermal investigations indicate that all water molecules but one can be removed at temperatures below 160 °C and the last one by heating up to 340 °C. On further heating decomposition is observed.

Six new rare-earth metal tetracyanidoborates were prepared and characterized by single-crystal X-ray diffraction. Crystals of these salts contain co-crystallized solvent molecules, such as water, acetone, ethanol, or diethyl ether. In [La(EtOH)(3)(H2O)(2){B(CN)(4)}(3)] (1), [La-(EtOH)(H2O)(4){B(CN)(4)}(3)]Et2O (2), and [Y(EtOH)(H2O)(4){B(CN)(4)}(3)]EtOH (6) the tetracyanidoborate anions are all or in part bonded to the RE3+ ions, whereas in [Pr(H2O)(9)][B(CN)(4)](3)(CH3)(2)CO (3), [Er(H2O)(8)]-[B(CN)(4)](3)(CH3)(2)CO (4), and [Lu(EtOH)(H2O)(7)][B(CN)(4)](3)EtOH0.5H(2)O (5) the [B(CN)(4)](-) anions are not coordinated to the central metal atoms. Only in 1, one of the three crystallographically independent [B(CN)(4)](-) anions acts as a bridging ligand.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

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)]center dot nH(2)O. Two groups of isostructural compounds were obtained with the formulas [RE(H2O)(8)][B(CN)(4)](3)center dot nH(2)O (structure I) and [RE(H2O)(7){(KN)-N-1-B(CN)(4)}][B(CM4](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 N-1-B(CN)(4)}](2+) in structure II. The heating of the compounds to temperature of ca. 160 degrees C gives anhydrous samples, but elongated heating to temperatures above ca. 200 degrees 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.

Crystals of two groups of the new title compounds, which differ in their amount of coordinated and crystallized water molecules are obtained after evaporation of the solvent.