Alkaline-earth-metal thiocyanates M(SCN)2(M = Mg, Ca, Sr and Ba) in non-aqueous solution have been investigated by IR and Raman spectroscopy. The following aprotic solvents given in the order of increasing associating power have been used: N, N-dimethylformamide (DMF), acetone, acetonitrile (MeCN), tetrahydrofuran (THF) and methylacetate (MeCO2Me). These salts are in part dissociated in DMF while in the other solvents the predominant species are neutral molecules M(NCS)2 and dimers. The three dimers which have been identified are Ca2(NCS)4, Sr2(NCS)4 and Ba2(NCS)4. The stability of these species is ensured by N–µ2 SCN bridges between both cations, and increases in the order Ca < Sr < Ba. The thermodynamic investigation of the ion pairing of Mg2+ with SCN– in DMF and of the dimerization of Ba(NCS)2 in THF shows that both reactions are entropy-driven processes.
在非
水溶液中,碱土
金属
硫氰酸盐 M(SCN)2(M = Mg, Ca, Sr 和 Ba)已通过红外光谱和拉曼光谱进行了研究。使用的无质子溶剂按亲和力递增的顺序为:
N,N-二甲基甲酰胺(
DMF)、
丙酮、
乙腈(MeCN)、
四氢呋喃(THF)和
乙酸甲酯(MeCO2Me)。这些盐在
DMF 中部分解离,而在其他溶剂中,以中性分子 M(
NCS)2 和二聚体为主要物种。已识别的三种二聚体为 Ca2(
NCS)4、Sr2(
NCS)4 和 Ba2(
NCS)4。这些物种的稳定性由阳离子之间的 N–µ2 SCN 桥接确保,其稳定性随顺序 Ca < Sr < Ba 增加。对 DMF 中 Mg2+ 与 SCN– 的离子对形成以及 THF 中 Ba(
NCS)2 的二聚化的热力学研究表明,这两种反应都是由熵驱动的过程。