Synthese und strukturchemische Untersuchungen an molekularen Oxovanadiumphosphonaten

Solvothermal syntheses at 373 K in the system MePPh3)[VO2Cl2]/ RPO3H2 (R = tBu; Ph)/Template (T = Cl-, HCl, OH-; Br-) /MeCN have lead to the already known compound [(VO)(6)(tBuPO(3))(8) subset of Cl-] (1) [1] as well as to [(VO)(6)-(tBuPO(3))(8) subset of T](T: HCl (2) OH- 3), [(VO)(6)(PhPO3)(8) subset of Br-]Xsolv (4), (Ph3PMe)(2)[(VO)(6)(PhPO3)(8) subset of Cl-](3) (5) with an identical VPO-core, and [(V3O5)(VO)(4)(tBuPO(3))(8) subset of NO3-] (6) with seven metal centres. The renewed X-ray structure analysis of 1 produced evidence, that the {V6P8O24}-core shows some flexibility and belongs to the enantiomorphic point group O ( 432). With the structure data from the compounds 1-5 a geometric model for the flexible contraction of the {V6P8O24}-core was developed. The calculation of the diameter of the host shell for different degrees of contraction shows that the {V6P8O24}-core is always too small to incorporate a nitrate ion. This leads to the formation of [(V3O5)(VO)(4)(tBuPO(3))(8) subset of NO3-] (6) which can be derived topologically from 1. There is no structural similarity between 6 and the seven oxovanadium units containing anion of (Ph4P)(2)[(V4O7)(V3O5)(PhPO3)(6) subset of Cl-] [2]. The thermal degradation of I in air starts at 590 K with the oxidation of the organic groups followed by the formation of beta-(VO)(PO3)(2). Possibly these results offer new ways to use oxovanadium phosphonates as precursors of oxovanadium phosphate catalysts.