Reaction of [Nb6O19](8-) with H6TeO6 in water gives telluropentaniobate [(OH)TeNb5O18](6-) (1) as single product, which was isolated as Na+ and mixed Na+/K+ salts. Crystal structures were determined for Na-6[(OH)TeNb5O18]center dot 15H(2)O (Na-6-1) and K6Na[Nb-5.5{Te(OH)}(0.5)O-18.5]center dot 26H(2)O (K6Na-1). Formation of 1 was monitored with electrospray ionization mass spectrometry (ESI-MS) and Te-125 NMR techniques. Capillary electrophoresis was used to calculate electrophoretic mobilities and radii of the anionic species in solutions of [(OH)TeNb5O18](6-) and [Nb6O19](8-) in borate buffer. No condensation or degradation products were detected. Reactions of 1 with {Cp*Rh}(2+) sources gives 1:1 and 2:1 hybrid polyoxometalate, which are present in solution as a mixture of isomers, as detected by Te-125 NMR The isomerism is related to various possibilities of coordination of {Cp*Rh}(2+) to different {M3O3} faces, relative to the unique Te atom. According to ESI-MS experiments in water and methanol, rapid redistribution of the organometallic fragments between the 1:1 and 2:1 complexes takes place. The 1:1 complexes are more stable in water, while 2:1 complexes dominate in methanol. X-ray structural analysis of the crystals isolated from 2:1 reaction mixture allowed identification of Na-3[{Cp*Rh}(2)TeNb5O19]center dot 24H(2)O (Cp*Rh-2(2)-1) with two {Cp*Rh}(2+) fragments capping the opposing faces of the Lindqvist anion.