Unique Aluminum Clusters Stabilized by Cation-Ligand Cooperativity

Two novel cyclic Al3 clusters, Li2[Al3(PR2)6] & sdot; 2(Et2O) [R=Ph (1), Cy (2)] were synthesized through salt metathesis of metastable AlCl & sdot; (Et2O)n solutions with LiPR2. Both complexes were characterized by single crystal X-Ray diffraction and their solid state and electronic structures are compared to previously reported cyclic Al3 clusters. Compounds 1 and 2 were further characterized using density functional theory (DFT) methods to understand the nature of the free electron and the three-center two-electron Al-Al bonds. Calculations revealed that both clusters are influenced by pseudo Jahn-Teller distortion and are likely in equilibrium between two low energy bonding states. The solid-state structures of 1 and 2 are unique among Al3 clusters, while the electronic structure is similar to the previously reported [Sit4Al3]. In aluminum chemistry, 1 and 2 are rare examples of clusters containing isoelectronic cores in different ligand environments. The effects of the phosphide ligand sphere and strongly coordinated lithium atoms are discussed in detail. Two novel low-valent Al3 phosphide clusters exhibiting radical character have been synthesized. Due to pseudo Jahn-Teller effects, the radical is predicted to rapidly interconvert between two low energy states at room temperature.+ image