School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
Chemistry. 2012 Jul 27;18(31):9580-9. doi: 10.1002/chem.201103379. Epub 2012 Jun 28.
A series of low-melting-point salts with hexakisdicyanonitrosomethanidolanthanoidate anions has been synthesised and characterised: (C(2) mim)(3) [Ln(dcnm)(6)] (1 Ln; 1 Ln=1 La, 1 Ce, 1 Pr, 1 Nd), (C(2) C(1) mim)(3) [Pr(dcnm)(6)] (2 Pr), (C(4) C(1) pyr)(3) [Ce(dcnm)(6)] (3 Ce), (N(1114))(3) [Ln(dcnm)(6)] (4 Ln; 4 Ln=4 La, 4 Ce, 4 Pr, 4 Nd, 4 Sm, 4 Gd), and (N(1112OH) )(3) [Ce(dcnm)(6)] (5 Ce) (C(2) mim=1-ethyl-3-methylimidazolium, C(2) C(1) mim=1-ethyl-2,3-dimethylimidazolium, C(4) C(1) py=N-butyl-4-methylpyridinium, N(1114) =butyltrimethylammonium, N(1112OH) =2-(hydroxyethyl)trimethylammonium=choline). X-ray crystallography was used to determine the structures of complexes 1 La, 2 Pr, and 5 Ce, all of which contain Ln(dcnm)(6) ions. Complexes 1 Ln and 2 Pr were all ionic liquids (ILs), with complex 3 Ce melting at 38.1 °C, the lowest melting point of any known complex containing the Ln(dcnm)(6) trianion. The ammonium-based cations proved to be less suitable for forming ILs, with complexes 4 Sm and 4 Gd being the only salts with the N(1114) cation to have melting points below 100 °C. The choline-containing complex 5 Ce did not melt up to 160 °C, with the increase in melting point possibly being due to extensive hydrogen bonding, which could be inferred from the crystal structure of the complex.
(C(2) mim)(3) [Ln(dcnm)(6)]（1Ln；1Ln=1La、1Ce、1Pr、1Nd）、(C(2) C(1) mim)(3) [Pr(dcnm)(6)]（2Pr）、(C(4) C(1) pyr)(3) [Ce(dcnm)(6)]（3Ce）、(N(1114))(3) [Ln(dcnm)(6)]（4Ln；4Ln=4La、4Ce、4Pr、4Nd、4Sm、4Gd）和(N(1112OH))(3) [Ce(dcnm)(6)]（5Ce）（C(2) mim=1-乙基-3-甲基咪唑鎓，C(2) C(1) mim=1-乙基-2,3-二甲基咪唑鎓，C(4) C(1) py=N-丁基-4-甲基吡啶鎓，N(1114)=丁基三甲基铵，N(1112OH)=2-(羟乙基)三甲基铵=胆碱）。通过 X 射线晶体学确定了配合物 1La、2Pr 和 5Ce 的结构，它们都含有Ln(dcnm)(6)离子。配合物 1Ln 和 2Pr 都是离子液体（ILs），其中配合物 3Ce 的熔点为 38.1°C，是已知含有Ln(dcnm)(6)三阴离子的复合物中熔点最低的。铵阳离子被证明不太适合形成 ILs，只有具有 N(1114)阳离子的配合物 4Sm 和 4Gd 的熔点低于 100°C。含有胆碱的配合物 5Ce 直至 160°C 都没有熔化，熔点的升高可能是由于氢键的广泛存在，这可以从配合物的晶体结构推断出来。
