Tetracyanoborate Salts M[B(CN)₄] with M = Singly Charged Cations:  Properties and Structures

Abstract

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] x THF and [NH4][B(CN)4] x 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, Fd3m, a = 11.680(1) A, Z= 8; Li[B(CN)4], cubic, P43m, a = 5.4815(1) A, Z= 1; Cu[B(CN)4], cubic, P43m, a = 5.4314(7) A, Z= 1; Rb[B(CN)4], tetragonal, /4(1)/a, a = 7.1354(2) A, c= 14.8197(6) A, Z= 4; Cs[B(CN)4], tetragonal, /4(1)/a, a = 7.300(2) A, c = 15.340(5) A, Z= 4; [NH4][B(CN)4], tetragonal, /4(1)/a, a = 7.132(1) A, c = 14.745(4) A, Z= 4; Tl[B(CN)4], tetragonal, /4(1)/a, a = 7.0655(2) A, c = 14.6791(4) A, Z= 4; Na[B(CN)4] x THF, orthorhombic, Pnma, a = 13.908(3) A, b = 9.288(1) A, c = 8.738(1) A, Z= 4; [NH4][B(CN)4] x THF, orthorhombic, Pnma, a = 8.831(1) A, b = 9.366(2) A, c = 15.061(3) A, 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 A1 and T2 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.

Homoleptic Luminescent Lanthanide Frameworks with the Tricyanohydridoborate Anion

“…[2] Cyanoborate anions are also utilized as building blocks for manifold coordination compounds, comprising salts, molecular complexes and coordination polymers, which have mostly been obtained with the tetracyanoborate anion [B(CN) 4 ] -. [3][4][5][6] There are far less examples for related compounds that contain anions in which cyano groups are substituted with other groups, such as in the tricyanofluoroborate anion [BF(CN) 3 ] -. [7] Anhydrous, homoleptic frameworks 3 ∞ [Ln{C 2 F 5 B(CN) 3 } 3 ] (Ln = La, Eu, Ho) [8] could be obtained using (H 3 O)[C 2 F 5 B(CN) 3 ] and by an ionothermal approach.…”

“…[3][4][5][6] There are far less examples for related compounds that contain anions in which cyano groups are substituted with other groups, such as in the tricyanofluoroborate anion [BF(CN) 3 ] -. [7] Anhydrous, homoleptic frameworks 3 ∞ [Ln{C 2 F 5 B(CN) 3 } 3 ] (Ln = La, Eu, Ho) [8] could be obtained using (H 3 O)[C 2 F 5 B(CN) 3 ] and by an ionothermal approach. [9] To the best of our knowledge, hydrido-substituted cyanoborates such as the tricyanohydridoborate anion [BH(CN) 3 ] -have hardly been used for metal coordination.…”

“…[7] Anhydrous, homoleptic frameworks 3 ∞ [Ln{C 2 F 5 B(CN) 3 } 3 ] (Ln = La, Eu, Ho) [8] could be obtained using (H 3 O)[C 2 F 5 B(CN) 3 ] and by an ionothermal approach. [9] To the best of our knowledge, hydrido-substituted cyanoborates such as the tricyanohydridoborate anion [BH(CN) 3 ] -have hardly been used for metal coordination. [10] Recently, efficient syntheses for the potassium salt of the latter anion, K[BH(CN) 3 ], have been developed [10c,10d] and the latter proved to be a suitable starting point for the synthesis of the oxonium salt (H 3 O)[BH(CN) 3 ] [11] or for K 2 [B(CN) 3 ].…”

“…[9] To the best of our knowledge, hydrido-substituted cyanoborates such as the tricyanohydridoborate anion [BH(CN) 3 ] -have hardly been used for metal coordination. [10] Recently, efficient syntheses for the potassium salt of the latter anion, K[BH(CN) 3 ], have been developed [10c,10d] and the latter proved to be a suitable starting point for the synthesis of the oxonium salt (H 3 O)[BH(CN) 3 ] [11] or for K 2 [B(CN) 3 ]. [12] A variety of miscellaneous synthetic approaches towards coordination compounds and polymers have been reported including acid/base reactions, [13,14] anion metatheses in solution [15] as well as sintering techniques, [16] and transformation of ionic liquids.…”

“…[21] Ligands that function as effective sensitizers can be of great importance for intense lanthanide-based emission. [22] Here, we report on the synthesis and characterization of the first lanthanide tricyanohydridoborates 3 ∞ [Ln{BH(CN) 3 3 ] -anions leads to the homoleptic frameworks 1 and 2 upon complete substitution. The solid reaction products show intensive and characteristic photoluminescence upon excitation with a UV lamp.…”