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

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.