Hydroxytricyanoborate Anion: Synthetic Aspects and Structural, Chemical, and Spectroscopic Properties

In recent years, salts of the hydridotricyanoborate anion [BH(CN)₃]^- (MHB) have become readily available. In spite of the unusually high stability of the MHB anion, it can be used as a valuable starting material for the preparation of selected tricyanoborates, for example, the boron-centered nucleophile B(CN)₃^2-. A further unprecedented example is the hydroxytricyanoborate anion [B(OH)(CN)₃]^- that is accessible by oxidation of (H₃O)MHB with elemental bromine in water. The Brønsted acid (H₃O)[B(OH)(CN)₃] was isolated as a crystalline solid. It serves as a versatile starting material for the synthesis of coordination compounds, metal salts, and ionic liquids. The [B(OH)(CN)₃]^- anion shows a rich coordination chemistry and a high tendency to form hydrogen-bonded motifs as demonstrated by a series of salts with different types of cations. Furthermore, the [B(OH)(CN)₃]^- anion itself serves as starting material for new tricyanoborates such as the unusual trianion [B{OB(CN)₃}₃]^3- and the silylated anions [B(OSiR₃)(CN)₃]^- (R = Me, Et, Ph). Some of these follow-up products have been characterized by single-crystal X-ray diffraction, e.g., [nBu₄N]₃[B{OB(CN)₃}₃] and [nBu₄N][B(OSiPh₃)(CN)₃].

Poly[tetrakis(μ-1,1,1,3,3,3-hexafluoropropan-2-olato)iron(II)dipotassium]

The title compound, [K2Fe{OCH(CF3)2}4] n , was formed from the reaction of potassium hexa-fluoro-isopropoxide with iron(II) chloride in toluene. The Fe(II) atom has a highly distorted tetra-hedral coordination environment. All four of the non-equivalent hexa-fluoro-isoprop-oxy O atoms link the Fe(II) atoms to one of the K(+) atoms in an alternating chain of Fe-O-K-O fused four-membered rings, with K-Fe distances of 3.715 (2) and 3.717 (2) Å. This K(+) atom is also bridged to eight of the F atoms. The other K(+) atom is bonded to only two of the O atoms, but has seven short K⋯F contacts, one of which links the chains into a three-dimensional arrangement. Weak hydrogen bonding between the lone H atoms on the hexa-fluoro-isoprop-oxy groups and F atoms is also present. The crystal studied was refined as an inversion twin.