Reaction of truns-[a2PtL212+ (a = NH3 or CH3NH2; L = 1-methylcytosine, CSHTNJO, or l,S-dimethylcytosine, CsH9N3O) with HgO in water yields novel heteronuclear Pt-Hg compounds containing two bridging cytosyl ligands L-, binding to Pt via N3 and to Hg via the deprotonated exocyclic amino group N4. Three representative examples have been characterized by X-ray crystallography: transrs-[(CH3NH2)2Pt( 1-MeC-)2Hg](NOs)2 (ld), truns-[(CH3NH2)2Pt(l,5-DimeC-)2Hg](N03)~0.5H20 (M), and truns-[(CH3NH2)2Pt(l-MeC-)2Hg]Cl(NO3) (le). Crystal data are as follows: Id, triclinic system, space group Pi, u = 10.157(4) A, b = 10.494(4) A, c = 11.452(4) A, cy = 101.33(2)O, B = 102.44(2)O, y = 104.65(2)O, Y = 11 11.8(7) A3,Z = 2; le, monoclinic system, space group a / m , u = 13.876(4) A, b = 16.254(3) A, c = 10.358(3) A, p = 112.02(1)O, V = 2166(1) A3, Z = 4; M, monoclinic system, space group n l / n , u = 8.614(3) A, b = 20.610(6) A, c = 13.984(5) A, fl = 97.67(2)O, V = 2461(2) A3, Z = 4. In all three compounds, Pt displays a square-pyramidal coordination sphere, with Hg in the apical position.Hg has severely distorted coordinations with two short Hg-N(4) distances, a Hg-Pt contact, and longer Hg-03Ndistances in Id (distorted octadedron) and 2d (distorted bipyramid), whereas in l e the coordination around Hg is completed by C1-(distorted bipyramid). Pt-Hg separations are 2.785(1) A (ld), 2.765(1) A (2d), and 2.835(1) A (le), and interactions are interpreted in terms of weak Pt-Hg bonds. The I95Pt NMR spectra of the Pt-Hg compounds display 199Hg satellites due to IJ coupling, consistent with Pt-Hg bonding. lH NMR spectra of the various Pt-Hg compounds show 195Pt and 199Hg coupling, as determined by decoupling and spectral editing techniques.Unlike related Pt-Pt compounds, the mixed-metal Pt-Hg species, when reacted with a large variety of N and S donor ligands X, tend to decompose with formation of trans-[a2PtL2l2+ and HgX2. IntroductiooMetal-metal bonding in heteronuclear complexes containing both d* and d10 metal ions has been known for some 25 yeam2s3 A rich chemistry has been established for such species, in particular for the following combinations: Irl and Au1,4 Irl and Ag1,'ls6 P t l l and Hg11,7-9 P t l I and Ag1,lO-I3 and P t I I and Au1,14Js as well as Rhl

The molecular structure of trans-[(NH&Pt@-l-MeC-)2Pd(NH3)] [Pd(NH3)4]0.5(N03)3-3H20 (1) has been determined by X-ray crystallography. The compound crystallizes in the triclinic space group P i (No. 2), with a = 7.476 (2) A, b = 11.373(3) A, c = 16.397(4) A, a = 87.27(2)", , 8 = 85.32(2)", y = 88.74(2)", and Z = 2. The structure was refined to R = 0.034 and R, = 0.038 for 5045 independent reflections. The complex is best described by a square planar coordination of Pd and a square pyramidal one of Pt with the Pd in the apical position (T over square geometry, TSQ). The Pt and Pd atoms are bridged by two nearly coplanar 1-methylcytosinate anions with a Pt-Pd distance of 2.511(1) A. A theoretical analysis, based on EHMO calculations, highlights the nature of the single M-M' bond in d8-d8 dimers of this type (4:3) and points out the correlations with the better known ds-ds dimers (4:4) characterized by two parallel square planar coordination geometries. The M-M' bond order in the latter is close to zero, but not null. Finally, the fate of the M-M' linkage for adding one or two electrons to the above TSQ species is formally analyzed. A correlation is made with the structural data available for dimers with ds-d9 and ds-dIo electron counts [e.g. Pt(I1)-Cu(1I) and Pt(I1)-Hg(I1) species with bridging nucleobases]. While one additional electron weakens the M-M' linkage without destroying the primary TSQ geometry, two extra electrons force the expulsion of the ligand formerly coaxial with the metals (4:2 adducts). The M-M' interaction in the 4:2 adducts is comparable with that proposed for the 4:4 species.

A mechanism goes platinum: Hydrolytic deamination of cytosine is a major mutagenic event in DNA. Studies with a model system and DFT calculcations demonstrate that deamination is facilitated by coordination of the PtII center to the N3 atom (see scheme; C=cytosine, U=uracil).

Aerogels belong to the large class of porous solids. They are characterized by a network of a mechanically stable solid, most likely inorganic in nature comprising a large gas volume in comparison to the volume of the solid material. Although a large variety of aerogels with silicate networks already exist, examples for materials with transition metal oxide networks are rare. One particularly interesting target is zinc oxide because of its semiconducting and multifunctional character. A sol−gel process facilitating an organometallic precursor system is established. The mechanism of gelation has been studied in detail. Unlike most other sol−gel processes, at first a large number of nanocrystalline ZnO particles are formed that rapidly agglomerate to secondary aggregates instead of forming a network directly. Thus, these secondary aggregates determine the textural properties of the pore walls as they assemble into the final, highly cross-linked network. A monolithic ZnO aerogel with porosities greater than 99% could be received after solvent extraction with supercritical CO2. Furthermore, the porosities could be tuned via a combination of conventional drying and supercritical solvent extraction by a process that we call scalar drying. Finally, one of the potential functional properties of the new ZnO aerogels was proven, its application in photocatalysis.

The preparation of materials characterized by three types of porosity could be prepared by a continuous chemical gas-phase method. The multistep formation mechanism involves a critical temperature gradient and occurs within seconds. The resulting hollow aerogel materials show superior properties as gas sensors in comparison to materials constructed from compact nanoparticles.