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 D3h 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.