Tetracyanoborate (tetracyanidoborate or tetracyanoboranuide) is an anion or salt of this anion. It has four cyano groups attached to a central boron atom. The formula is [B(CN)4]−.
The anion is weakly coordinating and stable in conjunction with the hydronium ion H3O+.
Tetracyanoborate can form ionic liquids with unsymmetrical quaternary nitrogen cyclic cations. These are under investigation as carbon dioxide absorbers for use in carbon capture and storage. They are also used as electrolytes in supercapacitors and electric batteries.
Tetracyanoborate compounds were first made by Eduard Bernhardt and team in 2000 after previous failed attempts in the 1950s.
Production Tetrabutylammonium bromide can react with boron trihalides and potassium cyanide to yield tetrabutylammonium tetracyanoborate.
Tetrafluoroborate salts can react with Me3SiCN when catalysed with Lewis acids to substitute fluoride with cyanide yielding tetracyanoborates.
Hydrogen tetracyanoborate can react with metal oxides or hydroxides to yield tetracyanoborate salts.
Potassium tetracyanoborate can react in a metastases with another metal salt to yield insoluble tetracyanoborates.
A low cost generation route is to use potassium fluoroborate with excess lithium chloride and potassium cyanide with a metal hydroxide.
Related ions The related hexacyanodiborane(6) dianion [B2(CN)6]2− has a boron to boron bond, and forms salts.
The tricyanoborate dianion B(CN)32− can be used to generate various other substituted tricyanoborate ions.
The tetrakis(trifluoromethyl)borate anion, [B(CF3)4]- is also weakly coordinating and stable.
List nameformulacrystalspace groupunit cellvolumedensitycommentreferencelithium tetracyanoborateLi[B(CN)4]cubicP3ma = 5.4815 Z = 1164.7021.228colourless; zero thermal expansionbis(12-crown-4)-lithium tetracyanidoborate[Li(C8H16O4)2][B(CN)4]orthorhombicPnnaa=10.9239 b=20.2493 c=11.3254(μ2- tetracyanidoborate)-(15-crown-5)-lithium[Li(C10H20O5)][B(CN)4]monoclinicP21/ca=15.8412 b=16.1149 c=16.3793 β=116.468°Ph3C+[B(CN)4]−ammonium tetracyanoborate[NH4][B(CN)4]tetragonalI41/aa = 7.132 c = 14.745 Z = 4750.01.177colourless[NH4][B(CN)4]·THForthorhombicPnma a = 8.831 b = 9.366 c = 15.061 Z = 41245.71.093 colourless[CH3NH3][B(CN)4]monoclinicP21/c a=7.5865 b=16.504 c=6.5100 β=93.512°N-methylmethanaminium tetrakis(cyano)borate[(CH3)2NH2][B(CN)4]tetragonalI41/acda=12.8185 c=24.269 Z=163987.71.073 melt 129 °Ctetrabutylammonium tetracyanoborate[Bu4N][B(CN)4]orthorhombicPnmaa = 17.765 b = 11.650 c = 11.454 Z = 4 2370.5colourless; melt 316.2K1-ethyl-3 methylimidazolium tetracyanoborateliquid1-hexyl-3-methylimidazolium tetracyanoborateliquid1-butyl-2-methyl-3-methylimidazolinium tetracyanoborateliquid1-butyl-1-methylpyrolidinium tetracyanoborate[BMPyr][B(CN)4]liquid1-butyl-1-methylpiperidinium tetracyanoborateliquid1-pentyl-1-methylpyrolidinium tetracyanoborateliquidspiro-(1,1)-bipyrrolidinium tetracyanoborateOrganic ionic plastic crystal>−55 °C; mp 242 °C4-(pyridin-4-yl)pyridin-1-ium tetrakis(cyano)boratemonoclinicP21/ca=8.3394 b=9.7679 c=17.6562 β=96.127° Z=41430.01.264melt 214 °CN-benzyl-N,N-dibutylbutan-1-aminium tetrakis(cyano)borateorthorhombicPna21a=18.8990 b=15.6383 c=8.4712 Z=82136.81.212melt 59 °C(S)-Alanine ethyl ester tetracyanidoborate(C5H12NO)[B(CN)4]monoclinicC2a=17.059 b=8.7467 c=18.855 β=111.468° Z=82618.2 melt 110 °C; colourlessPyridinium tetracyano-borateorthorhombicPbcaa=13.200 b=7.600 c=21.300 Z=42503.71.038melt 137 °Ctetrabutulphosphonium tetracyanoboratenBu4P[B(CN)4]melt 316.2Ktetraphenylphosphonium tetracyanoboratePh4P[B(CN)4]melt 466.2[nBuPh3P][B(CN)4]melt 73 °C dec 374 °C[EtPh3P][B(CN)4]orthorhombicPnnaa = 14.1777 b = 13.4214 c = 12.3199 Z = 42344.291.151melt 98 °C dec 370 °C[nBu4P][B(CN)4]orthorhombicPnnaa = 18.2187 b = 12.0707 c = 11.6704 Z = 42566.50.968melt 73 °C dec 372 °C[Ph4P][B(CN)4]tetragonalI2da = 12.948 c = 29.382 Z = 849251.225melt 193 °C dec 390 °C2-hydroxyethyl-triphenylphosphonium tetracyanidoborateC20H20OP[B(CN)4]monoclinicP21/na = 14.1418 b = 10.5821 c = 15.4684 β = 94.622°2307.32colourless; triphenyl-N-(triphenylphosphoranylidene)phosphoraniminium tetrakis(cyano)boratemonoclinicP21/na=10.732 b=24.966 c=13.375 β=101.77° Z=435081.237melt 162 °CH[B(CN)4]hydroxonium tetracyanoborateH3O[B(CN)4]H5O2[B(CN)4]sodium tetracyanoborateNa[B(CN)4]cubicFdma = 11.680 Z = 81593.41.150colourless; giant negative thermal expansion 100K to 650KNa[B(CN)4]·THF,orthorhombicPnmaa = 13.908 b = 9.288 c = 8.738 Z = 41128.81.236colourless12-crown-4[Na(C8H16O4)2][B(CN)4]orthorhombicPnnaa=10.8630 b=20.619 c=11.348915-crown-5[Na(C10H20O5)][B(CN)4]monoclinicP21/ca=12.8859 b=14.2646 c=10.0379 β=91.975°Mg[B(CN)4]2[Mg(H2O)2][B(CN)4]2tetragonalI3da=12.3940 c=9.2041 Z=41413.851.363[Mg(H2O)6][B(CN)4]2triclinicPa=9.0078 b=9.7507 c=11.589 α=82.034° β=68.642° γ=72.303° Z=2902.71.333[Mg(DMF)6][B(CN)4]2triclinicPa=8.6187 b=11.1119 c=12.2149 α=66.0996° β=75.570° γ=76.422° Z=11023.91.123potassium tetracyanoborateK[B(CN)4]cubicI41/aa = 6.976 c = 14.210 Z = 4 691.5[Ca(H2O)3][B(CN)4]2triclinicPa=9.5347 b=10.2205 c=10.4874 α=68.283° β=89.223° γ=63.152 Z=2832.451.292[Ca(H2O)2(CH3CN)][B(CN)4]2monoclinicP21/ca=12.2203 b=12.6637 c=13.5191 β=116.5381871.711.231Na[B(CN)4{Cr(CO)5}]Na[B(CN)4{Cr(CO)5}2]Na[B(CN)4{Cr(CO)5}3]Na[B(CN)4{Cr(CO)5}4]Na2[{Cr(CO)4(B(CN)4)}2]Na4[{Cr(CO)3(B(CN)4)}4]cube shaped complex[FeII{κ2ΝB(CN)4]}2][FeII(H2O)2{κ2ΝB(CN)4]}2]tetragonalI2da = 12.3662 c = 9.2066 Z = 4[FeIII(H2O)6][B(CN)4]3rhombohedralRca = 14.9017 c = 20.486 Z = 6[Fe(DMF)6][B(CN)4]triclinicPa = 8.6255(3) Å, b = 11.0544(4) Å, c = 12.2377 α=65.987° β=75.521° γ=76.639° Z = 1Co[B(CN)4]2·2H2OtetragonalI2da=12.2922 c=9.2235 Z=4Ni[B(CN)4]2·0.5H2Obis((ethane-1,2-diyl)-bis(diphenylphosphine))-nickel(ii) bis[tetrakis(cyanido)borate][Ni(dppe)2][B(CN)4]2monoclinicP21/ca =18.4584 b=13.3628 c =22.9747 β =105.253°yellowhexakis(pyridine N-oxide)-nickel(ii) bis[tetrakis(cyanido)borate][Ni(pyNO)6][B(CN)4]2Ra=12.9613 c =22.6070yellowtetrakis(dimethyl sulfoxide)-bis(tetrakis(cyanido)borate)-nickelNi(DMSO)4{NC-B(CN)3}2triclinicPa=8.9732 b=10.0327 c=16.9838 α=82.303° β=81.013° γ=72.357°colourlessbis((ethane-1,2-diyl)bis[oxo(diphenyl)-phosphine])-bis(tetrakis(cyanido)borate)-nickel(ii) dichloromethane solvateNi(dppeO2)2{NC-B(CN)3}2triclinicPa=10.9158 b=12.8898 c=13.2656 α=64.935° β=89.842° γ =72.389°cuprous tetracyanoborateCu[B(CN)4]cubicFdma = 5.4314 Z = 1160.231.849colourlessCu[B(CN)4]2monoclinicC2/ma = 13.185 b = 7.2919 c = 6.029 β = 93.02° Z = 2zinc tetracyanoborateZn[B(CN)4]2trigonalPm1a = 7.5092 c = 6.0159 Z = 1[Zn(DMF)6][B(CN)4]triclinicPrubidium tetracyanoborateRb[B(CN)4]tetragonalI41/aa = 7.1354 c = 14.8197 Z = 4754.531.764colourlessY(H2O)7{κ1N-B(CN)4}][B(CN)4]2Y(H2O)8][B(CN)4]3·3H2O[Y(H2O)8{B(CN)4}3]·H2OmonoclinicC2/ca=16.0468 b=20.5478 c=21.1799 β=112.259°[Y(EtOH)(H2O)4{B(CN)4}3]·EtOHorthorhobicP212121a=13.204 b=13.793 c=17.041[Ru(Cp)(C6H6)]B(CN)4[Ru4(Cp)4{B(CN)4}4]Ag[B(CN)4]cubicP 43ma = 5.732 Z = 1188.3negative thermal expansion 100-600Kcaesium tetracyanoborateCs[B(CN)4]tetragonalI41/aa = 7.300 c = 15.340 Z=4817.52.013colourlessLa{B(CN)4}3(H2O)5]·0.5H2OmonoclinicP21/n1∞[La(NO3)2[B(CN)4](H2O)4]monoclinicP21/ca=11.902 b=11.629 c=10.850 β=111.77° Z=41394.72.143colourlessEMIM 1-ethyl-3-methylimidazolium[EMIM] 1∞[LaNO3{B(CN)4}3(H2O)3]monoclinicP121/n1a=9.561 b=20.688 c=16.487 β=104.85° Z=431521.498colourlessLa(EtOH)3(H2O)2{B(CN)4}3monoclinicP21/n a=10.443 b=17.973 c=17.484 β=97.843°La(EtOH)(H2O)4{B(CN)4} ·Et2OorthorhombicPbcaa=18.513 b=19.067 c=21.460Ce{B(CN)4}3(H2O)5]·0.5H2OmonoclinicP21/na=15.3808 b=10.8020 c=33.2887 β=103.250° Z=45383.51.443Pr{B(CN)4}3(H2O)5]·0.5H2OmonoclinicP21/na=15.393 b=10.777 c=33.205 β=102.961° Z=45368[Pr(H2O)9][B(CN)4]3·(CH3)2COmonoclinicC2/ca=16.119 b=20.638 c=21.572 β=111.961°Nd{B(CN)4}3(H2O)5]·0.5H2OmonoclinicP21/na=15.357 b=10.740 c=33.224 β=102.769° Z=45344Sm{B(CN)4}3(H2O)5]·0.5H2OmonoclinicP21/na=15.328 b=10.714 c=33.055 β=102.68° Z=45300Gd{B(CN)4}3(H2O)5]·0.5H2OmonoclinicP21/na=15.304 b=10.673 c=32.999 β=102.609° Z=45260Eu[B(CN)4]2•THFcubicFmma=12.2898 Z=41856.251.624Eu{B(CN)4}3(H2O)5]·0.5H2OmonoclinicP21/na=15.336 b=10.709=33.076 β=102.652° Z=45300Tb(H2O)7{κ1N-B(CN)4}][B(CN)4]2Tb(H2O)8][B(CN)4]3·3H2OmonoclinicC2/ca=15.9786 b=20.5317 c=21.1413 β=112.226°Dy(H2O)7{κ1N-B(CN)4}][B(CN)4]2Dy(H2O)8][B(CN)4]3·3H2OmonoclinicC2/ca=16.0293 b=20.5472 c=21.1881 β=112.234°Ho(H2O)7{κ1N-B(CN)4}][B(CN)4]2Ho(H2O)8][B(CN)4]3·3H2OmonoclinicC2/cEr(H2O)7{κ1N-B(CN)4}][B(CN)4]2monoclinicP21/na=13.7705 b=21.2528 c=19.1657 β=96.501°[Er(H2O)8][B(CN)4]3·(CH3)2COmonoclinicC2/ca=16.2090 b=20.5676 c=21.2564 β=112.379°Tm(H2O)7{κ1N-B(CN)4}][B(CN)4]2Tm(H2O)8][B(CN)4]3·3H2OmonoclinicC2/cYb(H2O)7{κ1N-B(CN)4}][B(CN)4]2Yb(H2O)8][B(CN)4]3·3H2OYb[B(CN)4]2•THFcubicFmma=12.1147 Z=41778Lu(H2O)7{κ1N-B(CN)4}][B(CN)4]2Lu(H2O)8][B(CN)4]3·3H2OmonoclinicC2/c[Lu(EtOH)(H2O)7][B(CN)4]3·EtOH·0.5H2Othallium tetracyanoborateTl[B(CN)4]tetragonalI41/aa = 7.0655 c = 14.6791 Z = 4732.572.895colourlessMercury(II)-bis(tetracyanoborate)Hg[B(CN)4]2trigonalPm1a = 7.8175 c = 6.0168 Z=1318.442.244Dimercury(I)-bis(tetracyanoborate)Hg2[B(CN)4]2orthorhombicPbcma = 5.689 b = 32.809 c = 6.0168 Z = 41389.63.016(μ-aqua)-bis(μ-tetracyanoborate)-aqua-leadPb2(H2O)4{B(CN)4}4triclinicPa=9.4912 b=9.901 c=10.1044 α=107.457° β=115.926° γ=101.328°753.02.086soluble in methanol and acetonitrile(μ-acetato)-(μ-tetracyanoborate)-ethanol-leadPb2(O2CCH3)2{B(CN)4}2(C2H5OH)2monoclinicP21/na=7.9955 b=17.4564 c=9.9725 β=97.429°1380.22.056
References