Abstract
The synthesis, structures and magnetic properties of an η(5)-silole complex and an η(5)-stannole complex of erbium are reported. The sandwich complex anions [(η(5)-Cp(Si))Er(η(8)-COT)](-) and [(η(5)-Cp(Sn))Er(η(8)-COT)](-), where Cp(Si) is [SiC(4)-2,5-(SiMe(3))(2)-3,4-Ph(2)](2-) (1(Si)), Cp(Sn) is [SnC(4)-2,5-(SiMe(3))(2)-3,4-Me(2)](2-) (1(Sn)) and COT=cyclo-octatetraenyl, were obtained as their [K(2.2.2-cryptand)](+) salts and found to be isostructural, with remarkably similar bond lengths and angles, differing only in the lengths of the Er-E interactions (E=Si, Sn). The parallels in the molecular structures of 1(Si) and 1(Sn) are reflected in their dynamic magnetic properties, which show single-molecule magnet behaviour in zero applied field, with effective energy barriers of 115±7 and 125±3 cm(-1), respectively, along with comparable magnetic relaxation times. Analysis of the two complexes using ab initio calculations reveals differences at a quantitative level, but overall similar electronic structures, with the thermally activated relaxation likely to proceed via the first-excited Kramers doublet. Comparing 1(Si) and 1(Sn) with the previously reported germanium analogue 1(Ge) reveals that swapping one heavier group 14 element for another in complexes of the type [(η(5)-Cp(E))Er(η(8)-COT)](-) has a minimal impact on the SMM behaviour.