Tri- and tetravalent and mixed-valence niobium complexes supported by a tripodal tripyrrolylmethane trianion

The reaction of Nb2Cl6(TMEDA)(2) with the potassium salt of tripyrrolylmeth ane in a 1:1 ratio afforded two products which have been isolated and chara cterized. The first compound is the dinuclear {[HC(C4H3N)(3)]Nb(THF)}(2). 2 THF (1), with two trivalent and diamagnetic metal centers bridged by two tr ipyrrolyl trianions. Each of the two ligands adopted a rather unusual bridg ing mode, with two rings each sigma -bonding one of the two metal. centers and the third both pi -bonded to one of the two niobium atoms and sigma -bo nded to the other. The second product of the reaction is {([H(C4H3N)(3)](2) NbK)(2)}{Nb4Cl11[K(THF)(2)](2)}. 2THF (2), which displays some unusual feat ures. The complex is ionic, with the cationic {Nb4Cl11[K(THF)(2)](2)}(2+) u nit containing the metal in a mixed-valence state. The two positive charges of the cationic moiety are balanced by two identical anionic {([HC(C4H3N)( 3)](2)NbK)(2)}(-) units, each containing Nb in the tetravalent state. Each anion is connected to an identical one by the bridging potassium atom, thus assembling a linear and anionic polymeric array. A similar reaction carrie d out with the lithium salt of the tripyyrolide anion led instead to the si mple monomeric and tetravalent complex {[HC(C4H3N)(3)](2)Nb}{Li(THF)(4)}(2) (3).