Molecular and Electronic Structure, and Hydrolytic Reactivity of a Samarium(II) Crown Ether Complex.

The reaction of SmI with dibenzo-30-crown-10 (DB30C10), followed by metathesis with [BuN][BPh], allows for the isolation of [Sm(DB30C10)][BPh] as bright-red crystals in good yield. Exposure of [Sm(DB30C10)] to solvents containing trace water results in the conversion to the dinuclear Sm complex, Sm(DB30C10)(OH)I. Structural analysis of both complexes shows substantial rearrangement of the crown ether from a folded, Pac-Man form with Sm to a twisted conformation with Sm. The optical properties of [Sm(DB30C10)][BPh] exhibit a strong temperature dependence and change from broad-band absorption features indicative of domination by 5d states to fine features characteristic of 4f → 4f transitions at low temperatures. Examination of the electronic structure of these complexes via ab initio wave function calculations (SO-CASSCF) shows that the ground state of Sm in [Sm(DB30C10)] is a 4f state with low-lying 4f5d states, where the latter states have been lowered in energy by ∼12 000 cm with respect to the free ion. The decacoordination of the Sm cation by the crown ether is responsible for this alteration in the energies of the excited state and demonstrates the ability to tune the electronic structure of Sm.