Alkali metal clusters aromaticity

Synthesis and Structure of Aromatic Alkali Metal Clusters Supported by Molybdenum Metalloligands... 

Polymetallic anions, prepared by dissolution of alloys of the alkali and post-transition metals in amine solvents (often with a complexand for the alkali metal cation), have been characterized in crystalline and solution phases. Clusters TlSng3, Ge92 (with 20 skeletal bonding electrons), Sn93- (21 skeletal e) and Bi95+ (22 skeletal e) possess a tricapped trigonal prismatic structure, symmetry D3A, with variations of dimensional detail which correlate with the electron population.291 292 This structure is a ctoso-deltahedron, and with 20 (2h + 2) skeletal electrons can be construed to be three-dimensionally aromatic.292 The 22e clusters M94 (M = Ge, Sn, Pb) occur as the C4v monocapped square antiprism, a nido polyhedron. 

Gileadi et al. showed that it was possible to obtain aluminum ion-conducting nonpolar aprotic solutions [54-56]. Aromatic solvents such as toluene and ethylbenzene can dissolve AlBrj or AljBrg and LiBr or KBr, thus forming clusters of M+ AIBr4 or M+AljBr," (M+ is the alkali metal ion) which conduct ions by a hopping-type mechanism (in contrast to the ion transport via frictional motion in polar systems). In such solutions it is possible to plate aluminum and thus form a surface film s free active metal electrode in aprotic media (provided that the aprotic media are sufficiently pure and do not contain atmospheric and/or protic contaminants) [57],... 

Calculated NICS values suggest their aromatic behavior which is reflected through their additional stability often rationalized via a shell filling model. Both AlyC" and AlyO" are stable species relative to their neighbours formed by changing the number of electrons and/or the number of A1 atoms Original cluster unit of Al7C is more or less remain undisturbed when it forms compounds with alkali metals. 

Molecular aromatic clusters " have also been studied. Gallium phos-phonate cages (Fig. 19) containing alkali metal ions, cyclic hydrocoppers,(Fig. 20), quasi-aromaticity in the transition metal clusters... 

Xu and Jin [171] investigated with DFT methods the geometrical and electronic structures and the vibrational frequencies of the low-lying states of alkali metal M[c-As4] (M = Li, Na, K, Rb, and Cs) clusters and alkaline earth metal M [c-As4] (M = Be, Ca, Sr, and Ba) clusters. The computational results showed that the square planar [c-As4] dianion can coordinate with metal atoms forming pyramidal M[c-As4] and M [c-As4] complexes. On the basis of structural and electronic criteria of aromaticity, along with the presence of six delocalized jt-electrons... 

A series of alkali metal and alkaline earth metal-arsenic clusters formulated as M[c-Ass] (M = Li, Na, K, Rb, Cs) andM [c-Ass]+(M = Be, Mg, Ca, Sr, Ba) were investigated by Xu and Jin [173] using DFT methods. All M[c-Assj andM [c-Ass]" clusters adopt a pentagonal pyramidal structure with Csv symmetry, its basal plane involving the planar pentagonal [c-Ass] anion. From molecular orbital and NICS analysis, it was established that each of these species had three delocalized n MOs that satisfied the 4h - - 2 electron counting rule and therefore exhibit n-aromatic character. 

Alexandrova, A. N. Boldyrev, A. I. o-Aromaticity and o-antiaromaticity in alkali metal and alkaline earth metal small clusters. J. Phys. Chem. A. 2003,107, 554—560. 

Metal organic frameworks (MOFs) are crystalline porous materials whose structure is constituted by metal ions or clusters of metal ions held in places by coordination with bipodal or multipodal rigid organic linkers [1 ]. Typical organic compounds employed for the synthesis of MOFs are aromatic polycarboxylates that coordinate by electrostatic and coordinative bonds with metal ions or metal clusters. The aromatic ring provides conformational rigidity of the linker, making possible the directionality of the interaction of the carboxylic acids with the metallic nodes. There have been reported MOFs for virtually all the transition metals and also for alkali earth and other nontransition metals [5-7]. 

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