Iron Salts with the Tetracyanidoborate Anion: [Fe^III(H₂O)₆][B(CN)₄]₃, Coordination Polymer [Fe^II(H₂O)₂{κ²N[B(CN)₄]}₂], and [Fe^II(DMF)₆][B(CN)₄]₂

Abstract

The reaction of Fe(OH)(3) with tetracyanidoboronic acid, H[B(CN)(4)]·xH(2)O, in water leads to the first examples of tetracyanidoborates with a triply charged metal cation, [Fe(III)(H(2)O)(6)][B(CN)(4)](3) (1). Using elemental iron powder as starting material, [Fe(II)(H(2)O)(2){κ(2)ΝB(CN)(4)]}(2)] (2) is obtained. Anhydrous iron(II) tetracyanidoborate, which is synthesized by heating of 2, is soluble in dry dimethylformamide. After evaporation of the DMF solvent, single crystals of the third title compound, [Fe(II)(DMF)(6)][B(CN)(4)](2) (3), are obtained. Compound 3 is the first metal tetracyanidoborate soluble in nonpolar solvents. The title compounds have been characterized by single-crystal X-ray diffraction (1 rhombohedral, R3c (no. 167), a = 14.9017(7) Å, c = 20.486(1) Å, Z = 6; 2 tetragonal, I42d (no. 122), a = 12.3662(3) Å, c = 9.2066(4) Å, Z = 4; 3 triclinic, P1 (no. 2), a = 8.6255(3) Å, b = 11.0544(4) Å, c = 12.2377(5) Å, Z = 1). The metal ions in all three compounds are octahedrally coordinated. Whereas 1 and 3 are built up from isolated complex ions, 2 comprises a coordination polymer, in which the Fe(II) ion is coordinated by two oxygen atoms of two water molecules in a trans orientation and four nitrogen donor atoms of the [B(CN)(4)](-) groups, which bridge between neighboring iron ions. The iron(III) ion in 3 is in a perfect octahedral environment, which is formed by the O atoms of 6 molecules of water. The single-crystal X-ray structures, vibrational spectra, thermal properties, solubilities, and electrochemical characteristics are reported and compared with those of other known tetracyanidoborates.

Rare‐Earth Tetracyanidoborate Salts – Structural Features and Properties Including Luminescence of [RE­(H2O)8][B(CN)4]3·nH2O and [RE­(H2O)7{κ1N‐B(CN)4}][B(CN)4]2 (RE = Y, Tb, Dy, Ho, Er, Tm, Yb, Lu; n ≤ 3)

“…[1][2][3][4][5][6] Tetracyanidoborates with large organic cations have low melting points and are classified as ionic liquids. Even though the anion has a weak coordination ability, network structures are observed quite often with strong Lewis acidic mono-or divalent metal cations.…”

“…[7][8][9][10][11][12][13][14][15][16][17] To date, only one tetracyanidoborate salt has been described with a triply charged metal cation, namely, [Fe(H 2 O) 6 ][B(CN) 4 ] 3 . [1] Tetracyanidoborate salts have been tested for many useful applications, for example, for use in ionic liquids, membranes, fuel cells, or as battery electrolytes. [18][19][20][21][22][23][24][25][26][27] To improve the knowledge about tetracyanidoborate salts with trivalent metal cations, we present in this paper the syntheses of heavy (late) rare-earth-metal tetracyanidoborate hydrates.…”

Lanthanide Coordination Polymers and MOFs based on the Dicyanodihydridoborate Anion

“…Cyanoborates are of increasing interest for chemistry and materials science, mostly as buildingb lock for ionic liquids (ILs) as such cyanoborate ILs [1] exhibit comparatively low viscosities, which enable them for use as electrolytes in solar cells. [2] The most prominent exampleso fc yanoborates involvecompounds with the [B(CN) 4 ] À anion that have becomea vailable for the first time in 2000. [3] In the past years, differents ynthetic approaches towardsn ovel tetracyanoborates were developed, ranging from acid/base-reactions, [4] and anion metatheses in solution, [3] over sintering techniques, [5] to ionothermal reactions under complete transformation of the used IL.…”

“…[2] The most prominent exampleso fc yanoborates involvecompounds with the [B(CN) 4 ] À anion that have becomea vailable for the first time in 2000. [3] In the past years, differents ynthetic approaches towardsn ovel tetracyanoborates were developed, ranging from acid/base-reactions, [4] and anion metatheses in solution, [3] over sintering techniques, [5] to ionothermal reactions under complete transformation of the used IL. [6] Thus, it was possible to synthesize ar ange of different tetracyanoborates with transition metal [7] and lanthanide cations.…”

Homoleptic Luminescent Lanthanide Frameworks with the Tricyanohydridoborate Anion

“…[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. [17] Be-products exhibit intense and characteristic photoluminescence in the visible region through lanthanide-specific 4f-4f transitions with long luminescence decay times typical for the respective lanthanide ions.…”