Heterotrimetallic compounds containing Mo–M–Li [M = K, Rb and Cs] clusters: synthesis, structure, bonding, aromaticity and theoretical investigations of Li2M2 [M = K and Rb] and Cs4 rings

Abstract

A new polydentate fac-trioxo molybdenum complex, [MoO₃L]³⁻ {LH₃ = nitrilotriacetic acid}, has been synthesized by the reaction of lithium molybdate with iminodiacetic acid. The trinegative complex anion coordinates the alkali metal cations, K⁺, Rb⁺ or Cs⁺. The potassium, rubidium and cesium complexes, [Li{K(H₂O)₂}MoO₃L]_n (1), [Li{Rb(H₂O)₂}MoO₃L]_n (2) and [Cs{Li(H₂O)}₂MoO₃L]_n (3), form heterotrimetallic coordination chains, containing planar rings of Li₂M₂ (M = K or Rb) and Cs₄. Theoretical investigations on these rings were carried out using NICS calculations and ab initio ring current maps, revealing aromaticity to be of limited significance.