One approach to overcome these challenges is to utilize the heaviest plumbole dianion, which lacks intermolecular Pb-Er interactions due to its weaker -donor ability. The heteroleptic COT-Er SMM IV with magnetic hysteresis up to 5 K was isolated by Ruben and Roesky. Later on, it was shown that by combining the COT and germole dianions, the Er complexes were isolated as monomeric V or polymeric species VI without -coordination. The use of the lightest congeners, siloles, led to ring-opening of THF (VII) due to the strong nucleophilicity of the silicon center. Avoiding THF as solvent circumvented this problem and the first silole COT complex with Er (VIII) was recently synthesized. The magnetic properties of all the erbium SMMs (IV-VIII) are primarily influenced by the equatorial crystal field provided by [COT] 2-ligands, despite variations in the heteroatoms, these changes do not significantly impact the SMM properties.