Coordination Capacity Of Keggin Anions As Polytopic Ligands: Case Study Of [Vnb12o40](15-)

Reaction of Na9H4[VNb12O40{NbO(CO3)}(2)] with [(C6H6)RuCl2](2) (molar ratio {VNb12} : {(C6H6)Ru} = 1 : 4) in aqueous solution gives a mixture of [alpha-{(C6H6)Ru}(4)VNb12O40](7-) and [alpha-{(C6H6)Ru}(3)VNb12O40](9-). Direct acetone diffusion into mother liquor leads to crystallization of Na6H[alpha-{(C6H6)Ru}(4)VNb12O40]center dot 41.25H(2)O (1), characterized by single crystal X-ray diffraction (SCXRD). This anion has four organometallic fragments coordinated to the alpha-Keggin type [VNb12O40](15-) backbone in different manner. Three {(C6H6)Ru}(2+) groups cap triangular faces and one group a rectangular face of [VNb12O40](15-). Equilibrated mixture of [alpha-{(C6H6)Ru}(4)VNb12O40](7-) and [alpha-{(C6H6)Ru}(3)VNb12O40](9-) was studied by H-1 DOSY NMR, HPLC-ICP-AES and HPLC-ESI-MS combined techniques. Direct chromatographic separation of these complexes results in unexpected transformation of both species into [alpha-{(C6H6)Ru}(5)VNb12O40](5-), isolated and characterized as Na-5[alpha-{(C6H6)Ru}(5)VNb12O40]center dot 16H(2)O (2). This anion contains five coordinated organometallic groups occupying both triangular and rectangular faces.