Aromaticity in alkali metal clusters: Role of the metalloligand and the size of the metal ion

Abstract

A new polydentate fac-trioxo molybdenum complex, [MoO₃L]^2- {L=iminodiacetate} has been synthesized by the reaction of sodium molybdate and iminodiacetic acid. The dinegative complex anion acts as a ligand towards alkali metal cations, Na⁺. The sodium complex, [Na₂MoO₃L(H₂O)₂]_n (1) is a 3D hereto bimetallic coordination polymer, containing a unique hexagonal 1D sodium cluster chain. The DFT calculations on hexagonal sodium cluster show that, the (Na₆) rings in the chain are highly aromatic in character and the NICS (0) values of the Na₆ rings are almost same as their polyacene analogues. The stability and reactivity pattern of the Na₆ rings also follow the same pattern as their organic analogues. Related analysis on Li-cluster is also accomplished. A theoretical investigation based on DFT is performed to find out the possible stable structures of Li₆, Na₆, K₆, Li₃Na₃ and Na₃K₃ molecules and a common D_3h symmetric structure is found. Also the reactions between Li₆ and Na₆ as well as Na₆ and K₆ are found to be thermodynamically favourable. Importance of the presence of the metalloligand in inducting the aromatic behaviour is highlighted.