Reaction of zirconium tetrakis(tert-butoxide) (1) with dicylohexylphosphinic acid in toluene leads to the dinuclear compound [Zr(mu,mu'-O2P(cycl-C6H11)(2))(O-t-Bu)(3)](2) (2) in which the zirconium is pentacoordinated. An analogous reaction using diphenylphosphinic acid in tetrahydrofuran also leads to a dinuclear complex [Zr(mu,mu'-O2PPh2)(THF)((O-t-Bu)(3)](2).C6H5CH3 (3.C6H5CH3), in which zirconium is hexacoordinated. A novel exchange of tert-butoxy and phenoxy groups occurs when 1 is treated with diphenyl phosphate [(PhO)(2)PO2H] leading to the isolation of the exchange product [Zr{mu,mu'-O2P(O-t-Bu)(OPh)}(mu-OPh)(O-t-Bu)(2)](2) (4). In contrast to the above, trinuclear zirconium compounds Zr-3(mu,mu'-O2AsMe2)(2)(mu(2),mu'-O2AsMe2)(O-t-Bu)(7)(mu-O-t-Bu)(2) (5) and Zr-3(mu,mu'-O2P(O-t-Bu)(2))(5)(O-t-Bu)(7).1/2C(6)H(5)CH(3) (6.1/2C(6)H(5)CH(3)) have been isolated from the reaction of 1 with cacodylic acid and di-tert-butyl phosphate, respectively. The X-ray structures of 2, 3, 5, and 6 have been determined; although the X-ray structural analysis of 4 could not be satisfactorily finished, it reveals the disposition of the substituents. The solution state NMR data suggest that these compounds undergo structural changes in solution. Possible relationships among the various structures are discussed.