Abstract:Proceeding from the x-B-SbW,O,, fragment 1, various novel large heteropolyanions ([Na,Sb,W,,O, 3Z(H,0),]22~~ (2), [Sb,W,,0,,(OH),]'2~ ( 3 ) and (4); M"' = Fe3+, Co", Mn''. Ni") have been obtiiined in crystalline form by systematic synthesis. Their unexpected structures have been studied by X-ray diffraction: 2, 3 and 4 contain /j-SbW,l units connected to each other by Sb3 ions, WOJW0,OH groups. and WO,/M"+(H,O), groups. respectively. Structural details and especially the systematic synthesis strategy for the formation of these interesting polytungstates are discussed in order to explain the unusual behaviour of 1 in aqueous solulion under different rcaction conditions.

A series of novel manganese(II)-substituted polyoxometalates, [(MnII(H2O)3)2(WO2)2(BiW9O33)2]10- (1), [(MnII(H2O))3(SbW9O33)2]12- (2), and [(MnII(H2O)3)2(MnII(H2O)2)2(TeW9O33)2]8- (3), were synthesized and characterized by X-ray structure analyses. The use of these oxidatively and solvolytically stable heteropolyanions as homogeneous catalysts for the epoxidation of dienes was investigated by gas chromatography/mass spectrometry, IR spectroscopy, UV−visible studies, and cyclic voltammetric measurements. The catalytic performance is exemplified by the model substrate (R)-(+)-limonene, at ambient temperatures in a biphasic system, with excellent regioselectivities, >99%, and very high turnovers even with only a small molar excess of hydrogen peroxide.

The heteropolyanions [Bi 2 W 22 O 74 (OH) 2 ] 12-(1) and [X 2 W 20 M 2 O 70 (H 2 O) 6 ] (14-2n)-(X ) Sb 3+ , Bi 3+ ; M n+ ) Fe 3+ , Co 2+ , Zn 2+ ) (2-7) have been synthesized as alkali metal and ammonium salts, respectively, and characterized by elemental analysis, infrared spectroscopy, and X-ray crystallography. These tungsto bismutates and antimonates reveal one common feature: the trivacant -B-XW 9 O 33 Keggin fragment as the structural building unit. Formally, the unit can be derived from the Keggin structure by removing one trimetalate fragment, W 3 O 13 , and a 60°rotation of one of the remaining W 3 O 13 subunits around the X-O W3X bond vector (the subscript indicates the element(s) bonded). The unshared pair of electrons of the respective central, pyramidally coordinated heteroatom Sb III or Bi III prevents formation of the complete spherical structure. In the presented heteropolyanions 1-7, two -B-XW 9 O 33 units are connected by two WO 2 groups. Further stabilization of this hitherto unknown bis-decatungsto ion [X 2 W 20 O 70 ] 14-is reached either by addition of two formal fac-WO 3 anti-Lipscomb's rule units to give the bis-undecatungsto bismutate [Bi 2 W 22 O 74 (OH) 2 ] 12-(1) or by addition of two M n+ (H 2 O) 3 groups (M n+ ) Fe 3+ , Co 2+ , Zn 2+ ) forming the large, transition-metal-substituted heteropolyanion clusters [X 2 W 20 M 2 O 70 (H 2 O) 6 ] (14-2n)-(X ) Sb 3+ , Bi 3+ ; M n+ ) Fe 3+ , Co 2+ , Zn 2+ ) (2-7).

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