Cluster compounds giant

In the case of giant wheel (molybdenum blue) compounds, the general synthetic strategy involves the acidification (pH 1) and reduction of an aqueous molybdate(VI) solution [possible reducing agents iron powder, tin(II) chloride, molybdenum(V) chloride, ascorbic acid, cysteine, hydroxylamine, hypophos-phorous acid, sodium dithionite, or hydrazine sulfate].On the other hand, an icosahedral ball-shaped cluster can be formed in an aqueous Mo(VI)... 

The building block of each layer of 10 is the spherical icosahedral giant oxidized cluster cage of the Mo72Fe3o type but which now has a reduced metal-oxide-based cluster - the tetrahedral two-electron reduced Keggin [H2PM012040] ion-as nucleus (Figure 8). Like in the layer compound 8, each of the cluster-cluster composites is linked to four others via Fe-O-Fe bonds to form a layer structure. 

Pythagorean sense is that the giant cluster species - categorized on the basis of distinct, specific numbers - can themselves be used as synthons as they can be coordinatively linked together to form chains as well as layered compounds with properties relevant for materials science. 

As pointed out before, it can be hard to investigate supramolecular species in solution. This is true for a particula inorganic system, the so-called giant polyoxo-metalates prepared by Muller et al. Although these fascinating compounds are fully characterized, it was an open question as to if these large clusters can be dissolved and if crystallization is a driving force for their formation. 

At the time of discovery and publication, the M0154 Giant-Wheel-type cluster represented the largest cluster to be structurally characterized by single crystal X-ray diffraction. In itself, the synthesis of this giant cluster generated enormous interest, even in the popular scientific media. This is because the cluster is of nanoscopic dimensions, and as such, demonstrates potential to bridge the gap between the molecular world, characterized by small molecules or ions, and a world of macroscopic bulk compounds. 

Giant clusters can be obtained as pure compounds. The largc.st clusters that can still be crystallized for X-ray studies and are found to be of a defined nucleariiy... 

The cubic unit cell of YBgg-type compounds with 1632 boron atoms consists of 13 giant (B 12)13 icosahedra and 8 nonicosahedral B42 units [stmctural formula Bi2(Bi2)i2(B42)8] with the metal atoms statistically distributed on defined interstitial sites (Fig. 6) (46,47). The B42 units are clusters consisting of 80 boron sites with occupancies ranging between 28 and 71% (48). The homogeneity range is assumed to be considerable (YB , 20 < n < 100). Besides Y, most of the lanthanide and some actinide atoms are known to form this sUiicture (see Refs. 3,49, and 50). 

Detailed discussions on supramolecular structures of giant polyoxometalate clusters have been reported by Muller and co-workers." " The number of ionic lattices formed from anionic POM clusters and organic cations-coordination complex cations resulting in supramolecular structures is substantial and literally more than hundreds of new compounds in this class appear annuallyIn this overview, the supramolecular features of POM-based systems will be discussed mainly under three headings (a) supramolecular features of polyoxometalate supported transition metal complexes, (b) polyoxometalate-crown ether complexes with supramolecular cations, and (c) supramolecular water clusters associated with polyoxometalates. 

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