Di-, tri- and tetranuclear molecular vanadium phosphonates: a chloride encapsulated tetranuclear bowl

The reaction of vanadium(III) trichloride with tert-butylphosphonic acid (t-BuPO3H2) in the presence of 1,10-phenanthroline/2,2'-bipyridine as an ancillary ligand in acetonitrile at room temperature afforded two dinuclear dicationic vanadium(IV) complexes [(VO)(2)(phen)(2){t-BuPO2(OH)}(2)(OH2)(2)]center dot 2Cl [1] and [(VO)(2)(bipy)(2){t-BuPO2(OH)}(2)(OH2)(2)]center dot 2Cl [2]. On the other hand, when the reaction was carried out in methanol, the dinuclear vanadium(V) complex [(VO)(2)(bipy)(2)(mu(2)-O)(2)(t-BuPO3)(2)]center dot 2CH(3)OH center dot 0.5CH(2)Cl(2) [3] was isolated. While 1 and 2 contain two six-membered V2P2O4 rings, 3 contains a unique four-membered V2O2 ring. Replacement of tert-butylphosphonic acid by tritylphosphonic acid (Ph3CPO3H2) under the same reaction conditions in methanol leads to the formation of dicationic trinuclear vanadium(IV) complexes [(VO)(3)(phen)(3)(Ph3CPO3)(2)(OH2)(3)]center dot CHCl3 center dot 2(OH)center dot 2MeOH center dot 1.5H(2)O [4] and [(VO)(3)(bipy)(3)(Ph3CPO3)(2)(CH3OH)(3)](2)(OH)center dot 4CH(3)OH center dot 5H(2)O [5]. In these complexes, the triangular V(IV) platform is held together by two bicapping tripodal phosphonate ligands. Replacement of the chelating 2,2'-bipyridine ligand with 3,5-dimethyl-1H-pyrazole, under the same reaction conditions, afforded a tetranuclear vanadium(V) complex [{(VO)(4)(Ph3CPO3Me)(4)(mu-O)(4))Cl]{3,5-Me(2)PzH(2)}center dot 3C(7)H(8)center dot H2O center dot CH3OH [6]. Remarkably 6 possesses a unique bowl-shaped structure encapsulating a chloride anion.