Rare‐Earth Cyclobutadienyl Sandwich Complexes: Synthesis, Structure and Dynamic Magnetic Properties.

The potassium cyclobutadienyl [K2{η4‐C4(SiMe3)4}] (1) reacts with MCl3(THF)3.5 (M=Y, Dy) to give the first rare‐earth cyclobutadienyl complexes, that is, the complex anions [M{η4‐C4(SiMe3)4}{η4‐C4(SiMe3)3‐κ‐(CH2SiMe2}]2−, (2M), as their dipotassium salts. The tuck‐in alkyl ligand in 2M is thought to form through deprotonation of the "squarocene" complexes [M{η4‐C4(SiMe3)4}2]− by 1. Complex 2Dy is a single‐molecule magnet, but with prominent quantum tunneling. An anisotropy barrier of 323(22) cm−1 was determined for 2Dy in an applied field of 1 kOe, and magnetic hysteresis loops were observed up to 7 K. Squarocene complexes: The potassium cyclobutadienyl [K2{η4‐C4(SiMe3)4}] reacts with MCl3(THF)3.5 (M=Y, Dy) to give the first rare‐earth cyclobutadienyl complexes, that is, the anions [M{η4‐C4(SiMe3)4}{η4‐C4(SiMe3)3‐κ‐(CH2SiMe2}]2− (2M) as their dipotassium salts. The dysprosium complex 2Dy shows single‐molecule magnet behaviour, with an anisotropy barrier of 323 cm−1 and magnetization versus field hysteresis loops up to 7 K. [ABSTRACT FROM AUTHOR]