Tetracyanoborate salts M[B(CN)4]with M = Singly charged cations:: Properties and structures

A series of tetracyanoborate salts M[B(CN)(4)] with the singly charged cations of Li+, Na+, Rb+, Cs+, [NH4](+), Tl+, and Cu+ as well as the THF solvate tetracyanoborates Na[B(CN)4].THF and [NH4][B(CN)(4)].THF were synthesized and their X-ray structures, vibrational spectra, solubilities in water, and thermal stabilities determined and compared with already known M[B(CN)(4)] salts. Crystallographic data for these compounds are as follows: Na[B(CN)(4)], cubic, Fd (3) over barm a = 11.680(1) Angstrom, Z = 8; Li[B(CN)(4)], cubic, P (4) over bar 3m, a = 5.4815(1) Angstrom, Z = 1; Cu[B(CN)(4]), cubic, P (4) over bar 3m, a = 5.4314(7) Angstrom, z = 1; Rb[B(CN)(4)], tetragonal, l4(1)/a, a = 7.1354(2) Angstrom, c = 14.8197(6) Angstrom, Z = 4; Cs[B(CN)(4)], tetragonal, l4(1)/a, a = 7.300(2) Angstrom, c = 15.340(5) Angstrom, Z = 4; [NH4][B(CN)(4)], tetragonal, l4(1)/a, a = 7.132(1) Angstrom, c = 14.745(4) Angstrom, Z = 4; Tl[B(CN)(4)], tetragonal, l4(1)/a, a = 7.0655(2) Angstrom, c = 14.6791(4) Angstrom, Z = 4; Na[B(CN)(4)].THF, orthorhombic, Pnma, a = 13.908(3) Angstrom, b = 9.288(1) Angstrom, c = 8,738(1) Angstrom, Z = 4; [NH4][B(CN)(4)].THF, orthorhombic, Pnma, a = 8.831 (1) Angstrom, b = 9.366(2) Angstrom, c = 15.061(3) Angstrom, Z = 4. The cubic Li+, Na+, and Cu+ salts crystallize in a structure consisting of two interpenetrating independent tetrahedral networks of M cations and [B(CN)(4)](-) ions. The compounds with the larger countercations (Rb+, Cs+, Tl+, and [NH4](+)) crystallize as tetragonal, also with a network arrangement. The sodium and ammonium salts with the cocrystallized THF molecules are both orthorhombic but are not isostructural. In the vibrational spectra the two CN stretching modes A(1) and T-2 coincide in general and the band positions are a measure for the strength of the interionic interaction. An interesting feature in the Raman spectrum of the copper salt is the first appearance of two CN stretching modes.