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oxouranium(VI)34 (U-O = 2.34 (1), 2.31 (1) A and N-0 = 1.35(2) , 1.36 (2) A), and aquabis(l,2-dioxopyridinato)dioxouranium hydrate34 (U-O = 2.35 (1) A and N-O = 1.38 (2) A). Notice also that the U-O(TV-oxide) distances in 3 and 4 are significantly shorter than the U-O(P) distances. This is qualitatively consistent with the iV-oxide acting as the stronger base site.The chelate rings in 8-10 are approximately shaped in a chair cyclohexane ring conformation with the U-0=C bond angle greater than the U-0=P bond angle: 8, 137.6 (5) and 132.6 (3) °; 9, 140.7 (7) and 136.2 (6)°; 10, 141.0 (5) and 135.3 (3)°. The ligand "bite" angles (C)O-U-O(P) and nonbonded "bite" distances are 70.4 (2), 70.6 (3), and 71.8 (2)°a nd 2.781, 2.760, and 2.803 A, respectively. In 3 and 4, on the other hand, the chelate rings have a more irregular "twist-chair" cyclohexane configuration with the U-0=P bond angle slightly larger than the U-O-N bond angle: 3, 129.8 (6) and 127.2 (8)°; 4, 129.6 (9) and 124.0 (8)°. The bite angles (N)O-U-O(P) and nonbonded bite distances N(O)-(O)P are 70.0 (3)°a nd 2.742 A for 3 and 68.3 (4)°a nd 2.716 A for 4. The bite size represents ca. the 0-0 van der Waals distance in these ligands, a feature that may dictate the dihederal angle between the pyridyl ring and the plane defined by e.g. 0(10), P, and C(5) in 3 of approximately

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Three new series of transition metal complexes have been prepared from tetradentate Schiff base ligands with two sulfur and two nitrogen donor atoms. Ni(II), Cu(II), Pd(II), and Co(II) chelates were prepared with iV,A'-ethylenebis(monothioacetylacetonimine), H2 [(sacac)2en], W,W'-propylenebis(monothioacetylacetonimine), H2 [(sacac)2pn], and cis-N, '-cyclohexylbis(monothioacetylacetonimine), H2 [(sacac)2chxn], Zn(II) and Cd(II) chelates were also prepared with H2 [(sacac)2en] while trans-H2 [(sacac)2chxn] formed an isolable complex only with Pd(II). Characterization of the complexes by elemental analyses, molecular weight, magnetic susceptibility, and conductivity measurements and pmr, infrared, and electronic spectra has shown these chelates to be square-planar monomeric species with more charge delocalization in the sulfur-containing chelate rings than in the six-membered chelate rings in the oxygen analogs.