Among the large family of azaphospholes 1,2,4-diazaphospholes feature a particularly stable ring system. 3,5-Unsubstituted and 3,5-equally substituted 1,2,4-diazaphospholes and -diazaarsoles are best made from 1,3-bis(dimethylamino)-2-phospha/arsaallyl chlorides and hydrazines. This way four examples for single crystal X-ray structure investigations were prepared: The unsubstituted 1,2,4-diazaphosphole 2 and -diazaarsole 4, the N-substituted 1 -(2-pyridyl) 1.2.4-diazaphosphole 1, and the C-substituted 3,5-di-tert-butyl 1,2,4-diazaphosphole 3. They all possess planar rings with small angles at P (86°) and As (81°). The N-unsubstituted molecules are connected to each other by NH···N hydrogen bonds forming in case of the isotypic compounds 2 and 4 a helix along a crystallographic axis and in case of compound 3 for steric reasons a dimer. The structures of the aggregates found are compared to those of pyrazoles.

Tetraphenylphosphonium(arsonium) Octabromotriplumbate, Tetraphenylphosphonium Bromodichloroplumbate, Quantum Chemical Calculations [PhiPMPb^Brg] and [PhuAshtPb^Brg] crystallize both in the monoclinic space group Po2\ln. The lattice parameters of [PluPMPb^Brg] are a = 14.637(7), b = 8.151(3), c = 23.388(8) Ä, ß = 106.02(3)°, Z = 2 and of [PluAsMPbsBrg] are a = 14.697(7), b = 8.219(3), c = 23.527(8) A, ß = 106.27(3)°, Z = 2. The lattice parameters of [PhuPHPbBrClilCH^CN, which crystallizes in the triclinic space group (P I), are a = 9.435(3), b = 10.2577(14), c = 14.055(2) Ä, a = 88.320(11)°, ß = 84.82(2)°, 7 = 84.19(2)°, Z = 2. 207Pb NMR shifts of halogenoplumbates in solution are reported.

2,5-Dihydroimidazoline-l-oxyl radicals I, II with imino substituents coordinate to Pd(II) and Pt(II) complexes with formation of the N,N chelate complexes 1-6. With oxygen containing substituents either monodentate N-coordination to give 8 or N ,O chelate formation to give 9 takes place, depending on the position of the oxygen atom relative to the ring nitrogen atom. With radicals III that also have the second ring nitrogen atom oxidized and the Rh(III) or Ir(III) complexes [Cp*MCl2]2 the O , O chelates 11 -13 could be obtained, while with Na2PdCl4 the heterocycle was destroyed with formation of a N,N chelate complex 10 of an α-nitrosooxime ligand. The orthopalladated 2,2,5,5 tetramethyl-4-phenyl-2,5-dihydroimidazoline-l-oxyl complex 7a reacts with several a-amino acidates under splitting of the dichloro bridge with formation of the C,N/N,O-bis-chelate complexes 7b-f. The molecular structures of 2 and 10 were determined by X-ray diffraction.

The reaction of Cp*Co(CO)2 with thionylchloride in hexane affords the doubly bridged dimer (Cp*CoCl2)2. Whereas the same reaction in more polar solvents such as CH2Cl2 or thf gives the triply bridged dinuclear cations in the salt [(Cp*Co)2(μ-Cl)3]2 [Co2Cl6], no influence of the solvent is observed in the reaction of Cp*Co(CO)2 with thionylbromide, which results in the formation of the neutral dimer (Cp*CoBr2)2. The X-ray structure analysis of (Cp*CoBr2)2 shows two edge-sharing octahedra, while that of [(Cp*Co)2(μ-Cl)3]2[Co2Cl6] shows two facesharing octahedra in the cation and two edge-sharing tetrahedra in the anion.

Silicon, Supersilylsilanes, Van-der-Waals EffectsSupersilylsilanes R*SiX3 (R* = supersilyl = Si/Bu3; X = H, Me, /Bu, Ph, SiMe3, F, Cl, Br, I, OMe, OSÖ2CF3) are prepared (i) by reactions of supersilylhalosilanes with supersilyl sodium NaR* (Hal/R* exchange), (ii) by reactions of supersilylhalosilanes with hydride H" (Hal/H exchange), (iii) by reactions of supersilylsilanes with halogens Hal2 (H/Hal exchange, R*/Hal exchange), (iv) by reactions of supersilylhalosilanes with nucleophiles like F" , MeO-(Hal/F or Hal/OMe exchange) and (v) by reactions of supersilylsilanes with strong acids (H /0 S 0 2CF3 exchange). NMR chemical shifts <5(29Si) of the SiX3 groups of R*SiX3 strongly depends on the nature of X. The supersilylsilanes R*SiX3 are in part moisture sensitive (especially compounds with SiX3=SiHHal2 and SiH2Hal), in part sensitive against oxygen (compounds with SiX=SiBr or Sil), and some of them react with supersilyl sodium by supersilanidation (for example R*SiF3, R*SiH2Cl, R*SiMeHCl) or by reduction (for example R*SiCl3, R*SiMeBr2, R*SiPhBrCl). X-ray structure analyses of disilanes fBu3Si-SiX3 with SiX3=Si/Bu3, SiPh3, Sil3, SiPhCl2 show a staggered conformation. Due to steric repulsion of the /Bu3Si and SiX3 groups as well as van-der-Waalsoattraction of the substituents /Bu and X in /Bu3Si-SiX3 the SiSi bonds are longer than 2.34 A (the normal SiSi single bond length) and the torsion angles are smaller/larger than 60° (the ideal staggered conformation). From the extent of SiSi bond elongation and CSiSiX angle compression it is concluded that the bulkiness of X increases in direction Cl < I < Ph < SiMe3 < CMe3 (rBu3Si-Si?Bu3 has to date the longest SiSi bond of all disilanes) and the van-der-Waals forces between fBu/X increase in direction rBu/I < fBu/rBu < /Bu/Ph.