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The bis(acetyl)-bridged complex [{Pt(COMe) 2 } n ] (2) has been prepared from the platina-β-diketone [Pt 2 {(COMe) 2 H} 2 (µ-Cl) 2 ] (1) with hexamethyldisilazane. Reactions of complex 2 with the monodentate P and N donors PPh 3 , pyrazole (Hpz), pyridine (py), 4-methylpyridine (4-Mepy), and benzylamine (BnNH 2 ) resulted in the formation of the cis-diacetylplatinum(II) complexes cis-[Pt(COMe) 2 L 2 ] (L ) PPh 3 , 3; Hpz, 5; py, 6a; 4-Mepy, 6b; BnNH 2 , 7). Reactions with the bidentate N donors 2,2′-bipyridine (bpy), dimethylglyoxime (H 2 dmg), and pyridazine (pydz) resulted in formation of the complexes cis-[Pt(COMe) 2 (L∩L)] (L∩L ) bpy, 4; H 2 dmg, 8) and [Pt 2 (COMe) 4 (µ-pydz) 2 ] (9), respectively. Furthermore, complex 2 has been found to react with acids such as HX (X ) Cl, Br), generated in situ from Me 3 SiX/ H 2 O, acetylacetone (Hacac), and hexafluoroacetylacetone (Hhfacac) to yield the known platina-β-diketone 1, the new dinuclear bromo-bridged platina-β-diketone [Pt 2 {(COMe) 2 H} 2 (µ-Br) 2 ] ( 10), and new mononuclear platina-β-diketones [Pt{(COMe) 2 H}(L∩L)] (L∩L ) acac, 11; hfacac, 12). All complexes were characterized by means of microanalysis and IR and NMR spectroscopy. X-ray diffraction analyses were performed for complexes 10-12, showing a two-dimensional network built up by closed-shell Pt • • • Pt (d 8 -d 8 ) interactions and bifurcated hydrogen bonds in crystals of complex 10 as well as infinite platinum chains built up by closed-shell Pt • • • Pt (d 8 -d 8 ) interactions in crystals of complexes 11 and 12. Complexes 8, 11, and 12 have further been analyzed by UV/vis and luminescence spectroscopy in solution and in the solid state as well as time-resolved photo-emf measurements. Additionally, quantum chemical studies on the DFT level of theory revealed very strong O-H • • • O hydrogen bonds in the platina-βdiketones 10-12 (25.6-27.9 kcal/mol).

The energies of the kinetically inert, electronically saturated Lukehart-type metalla-beta-diketone [Re{(COMe)2H}(CO)4] (9 a) and of the kinetically labile, electronically unsaturated platina-beta-diketones [Pt{(COMe)2H}Cl2]- (10 a), [Pt2{(COMe)2H}2(micro-Cl)2] (11 a), and [Pt{(COMe)2H}(bpy)]+ (12 a) have been calculated by DFT at the B3LYP/6-311++G(d,p) level using effective core potentials with consideration of relativistic effects for the transition metals. Analogously, energies of the requisite open (non-hydrogen-bonded) equilibrium conformers (9 b, 10 c, 11 b, 12 b) and energies which were obtained from the hydrogen-bonded conformers by rigid rotation of the OH group around the C--O bond by 180 degrees followed by relaxation of all bond lengths and angles (9 c, 10 d, 11 c, 12 d) have been calculated. These energies were found to be higher by 14.7/27.2 (9 b/9 c), 20.7/27.2 (10 c/10 d), 19.2/25.7 (11 b/11 c), and 9.4/19.6 kcal mol(-1) (12 b/12 d) than those of the intramolecularly O--HO hydrogen-bonded metalla-beta-diketones 9 a, 10 a, 11 a, and 12 a, respectively. In acetylacetone (Hacac), the generic organic analogue of metalla-beta-diketones, the energies of the most stable non-hydrogen-bonded enol isomer (6 b) and of the conformer derived from the H-bonded form by rigid rotation of the OH group by 180 degrees followed by subsequent relaxation of all bond lengths and angles (6 k) were found to be 10.9/16.1 kcal mol(-1) (6 b/6 k) higher compared to the intramolecularly O--HO bonded isomer 6 a. Thus, the hydrogen bonds in metalla-beta- diketones must be regarded as strong and were found to be up to twice as strong as that in acetylacetone. A linear relationship was found between the hydrogen-bond energies based on the rigidly rotated structures and the OO separation in the hydrogen-bonded structures. Furthermore, these energies were also found to be correlated with the electron densities at the OH bond critical points (rhobcp) in the O--HO bonds of metalla-beta-diketones 9 a, 10 a, 11 a, and 12 a (calculated using the AIM theory). The comparison of the energies of the doubly intermolecularly hydrogen-bonded dinuclear platina-beta-diketone [{Pt{(COMe)2H}(bpy)}2]2+ (14) with that of the mononuclear intramolecularly hydrogen-bonded cation [Pt{(COMe)2H}(bpy)]+ (12 a) showed that the intermolecular hydrogen bonds in 14 are weaker than the intramolecular hydrogen bond in 12.

The studies on synthetic, spectroscopic and biological properties of platinum(IV) complexes, [PtCl(4)(R(2)eddp)] (R = Et, 1; n-Pr, 2), containing kappa(2)N,N' bidentate ligands, esters of ethylenediamine-N,N'-di-3-propionic acid (HOOCCH(2)CH(2)NHCH(2)CH(2)NHCH(2)CH(2)COOH, H(2)eddp), are reported. Complexes have been characterized by infrared, (1)H and (13)C NMR spectroscopy and elemental analysis and it was concluded that the coordination of the ligands occurs via nitrogen donor atoms of the ester ligands (R(2)eddp). Cytotoxicity studies were performed for ligand precursors and corresponding platinum(IV) complexes. Although the n-Pr(2)eddp.2HCl itself showed no activity (IC(50) values > 125 microM) in selected cell lines, the activity of complex 2, via apoptotic mode of cell death, has increased significantly for a broad range of cancer cell lines tested in vitro (IC(50) = 8.6-49 microM). As it was found that complexes 1 and 2 are able to interact with pBR322 plasmid DNA, platinum(IV) complexes of this type may act as drugs and pro-drugs.