The synthesis and characterization of new zirconium cluster compounds of composition H4Zr5Cl12(PR(3))(5) are reported. By reaction of ZrCl4 with 1.60 mol equiv of Bu(3)SnH followed by 1 mol equiv of PR(3), the pentanuclear species are obtained rather than the previously described hexanuclear ones, Zr6Cl14(PR(3))(4). The compounds with PR(3) = PMe(3) (1), PEt(3) (2), and PMe(2)Ph (3) have been characterized by X-ray crystallography and by P-31{H-1} and H-1 NMR spectroscopy. Compound 1.C6H6 crystallizes in the triclinic space group P (1) over bar with cell dimensions (-100 degrees C) of a = 11.833(2) Angstrom, b = 12.001(1) Angstrom, c = 20.167(2) Angstrom, alpha = 77.651(9)degrees, beta = 86.627(9)degrees, gamma = 64.23(1)degrees, V = 2517.4(5) Angstrom(3), and Z = 2. Compound 2 crystallizes in the monoclinic space group C2/c with cell dimensions (-75 degrees C) of a = 48.06(1) Angstrom, b = 12.667(2) Angstrom, c = 22.829(5) Angstrom, beta = 113.36(2)degrees, V = 12 758(11) Angstrom(3), and Z = 8. Compound 3 crystallizes in the triclinic space group P (1) over bar with cell dimensions (21 degrees C) of a = 12.623(2) Angstrom, b = 13.715(3) Angstrom, c = 19.382(4) Angstrom, alpha = 91.58(2)degrees, beta = 96.78(2)degrees, gamma = 116.20(1)degrees, V = 2878(2) Angstrom(3), and Z = 2. These diamagnetic compounds have NMR spectra showing that they retain solution structures that are similar to those in the crystals. Furthermore, the H-1 NMR spectra of 2 and 3 show resonances at -1.18 and -2.58 ppm, respectively, which integrate to four hydride ligands per Zr-5 cluster. In all cases, the Zr atoms define a distorted pyramid with a rectangular base. There are two long basal edges (3.41-3.54 Angstrom) and two short ones (3.20-3.31 Angstrom). The slant edges are similar in length (3.29-3.33 Angstrom) to the short basal edges. All eight of the Zr-Zr edges are bridged by a mu-Cl atom. One PR(3) ligand is bonded above the apical zirconium atom, and the others are bonded to the basal zirconium atoms, with two opposite ones in the basal plane and the other two below it. By using X-ray data collected at -100 degrees C, the four hydride ligands were found in (1.C6H6), two just inside the centers of the triangular Zr-3 faces with the longer basal edges [Zr-mu(3).H = 1.96(3) Angstrom] and two symmetrically placed below the short basal edges [Zr-mu(2).H = 1.96(8) Angstrom]. All four of these crystallographically independent hydrogen atoms refined well.