P. Bleckmann

Die kristallstruktur von hexamethylcyclotristannathian

Abstract The crystal structure of hexamethylcyclotristannathiane [(CH 3 ) 2 SnS] 3 was determined by means of X-ray single crystal methods (number of reflections: 1660; a = 9.685(3), c = 17.302(4) A; Z = 4; space group P 4 1 ). The six-membered ring (SnS) 3 has a twisted boat-conformation. The tin atoms are tetrahedrally surrounded by two carbon atoms (SnC = 2.16 A) and two sulfur atoms (SnS = 2.41 A). The existence of a second, unstable modification of [(CH 3 ) 2 SnS] 3 was established.

Dimethyl germylene insertion into a strained C-Ge bond and matrix isolation of tetramethyl digermene Me2Ge=GeMe2

Abstract Free tetramethyl digermene Me 2 Ge=GeMe 2 is generated thermally from molten 7,8-digerma bicyclooctadienes[2.2.2] which are obtained by germylene (Me 2 Ge) insertion into the C-Ge bond of corresponding 7-germa norbornadienes. The structure of the digermene follows from MS, matrix IR and Raman spectroscopy.

Determination of the structure of 1,1,3,3-tetrachloro-1,3-disilacyclobutane from Raman and infrared spectra

Abstract The structure of 1,1,3,3-tetrachloro-1,3-disilacyclobutane, (1) is confirmed by its infrared and Raman spectra. A planar structure for the four-membered ring has been established from frequency and intensity calculations of the infrared- and Raman-active vibrations. The infrared and Raman spectra of (1) were recorded in the solid state and by means of matrix isolation techniques. The results obtained lead to a reliable assignment of the observed bands to calculated frequencies.

Matrix Isolation and IR spectroscopy of stannylenes (CH3)2Sn and (CD3)2Sn

Abstract Free stannylenes Me 2 Sn and (CD 3 ) 2 Sn, generated thermally from the cyclic hexamers or by microwave discharge from Me 2 SnH 2 , are isolated by Argon matrix technique. All IR bands could be attributed to the important molecular vibrations by normal coordinate analysis. As shown by ab initio SCF calculations, Me 2 Sn has a singlet groud state, the angle CSnC is 95.3°, the CSn bond length is 2.203 A.

Calculation of the frequencies and intensities in the infrared and raman spectra of cyclopropenone

Abstract By using the values of the vibrational frequencies of normal and deuterated cyclopropenone (II- d 0 , II- d 2 ) and 16 O-and 18 O-substituted dimethylcyclopropenone (III) as -well as the infrared and Raman intensities of II a consistent set of force constants has been derived for the cyclopropenone skeleton. The derived values show that the zwitterionic form makes a substantial contribution to the electronic ground state of the molecule. The combined frequency and intensity calculation - simulation of the infrared and the Raman spectrum - is shown to be a good method for making a proper assignment of calculated and observed vibrations and deriving realistic sets of force constants.

Zur struktur von bis(trimethylsilyl)quecksilber

Abstract Structural data of crystalline (Me 3 Si) 2 Hg (I) have been determined by means of X-ray diffraction, IR, and Raman methods. The crystals are orthorhombic with a = 9.028, b = 15.244, c = 17.783 A. The space group is D 5 2 ( C 222 1 ) with 8 molecules in the unit cell. The SiHg bond length in the linear SiHgSi system is 2.500 ± 0.005 A. Infrared and Raman investigations in solution also led to the linear structure.

PREPARATION AND NMR INVESTIGATION OF 1,2-DISTANNYL AROMATICS AND HETEROAROMATICS, 1,2-DISTANNYLCYCLOALKENES AND 1,2-DISTANNYLCYCLOALKANES

A series of 1,2-distannylated aromatics, heteroaromatics and cycloalkenes was prepared by treating the dibromo precursors with Me3SnNa in tetraglyme. The latter were converted into the corresponding cycloalkanes by diimine reduction. Multinuclear NMR data are reported and discussed.

Vibrational Spectra of 2,2′-Pyridil and 2,2′-Pyridil-18O and Assignment of Infrared and Raman Bands

Abstract Vibrational spectra of 2,2′-pyridil and 2,2′-pyridil-18O in the solid state and in solutions have been measured in the Raman (4000–50 cm−1) and infrared (4000–100 cm−1). The assignment of the bands observed is performed using the group vibrational concept and isotopic shifts data of the normal modes. The presence of synand anti-phase vibrations of both pyridyl rings is discussed. The results are compared to the corresponding data for some similar molecules.

Characterization of the ‘surface enhanced Raman scattering’ by use of Raman-spectroscopic and quantum mechanical investigations of simple cluster compounds

Abstract This paper presents a characterization of the ‘Surface Enhanced Raman Scattering’ by use of Raman spectroscopic and quantum mechanical investigations of simple cluster compounds. It is shown that similarities exist between metal cluster complexes and molecules adsorbed on metal surfaces. The line intensities in Raman spectra of metal clusters are determined by means of a modified CNDO/2 method (1,2). Perturbation terms of an external electric field are inserted into the Hartree-Fock operator used in the CNDO/2 theory(1,2) to yield the induced dipole moment as a function of the normal co-ordinate q, from which the polarizability change upon q is obtained. The results for Ni 3 CO, Ni 7 CO, Ni 9 CO, Ni 10 CO and Ni 13 CO are discussed. In this manner we determine the number of metal atoms a cluster must contain before its properties are approximately indistinguishable from those of the bulk metal. Calculated intensities of the CO stretching vibrations of metal clusters agree well with experimental intensities obtained from Raman spectra of CO molecules adsorbed on Ni surfaces. In this manner we have obtained an approach for the description of ‘Surface Enhanced Raman Scattering’.

Determination of Raman intensities of lattice vibrations in crystalline urea

Abstract Quantum-chemical methods have been used for the calculations of the intensities of Raman-active lattice vibrations in crystalline urea. In a first step, the frequencies of the external vibrations in urea are calculated by use of the concept of flexible vibrating molecules within the intermolecular atom-atom forces. The quantum-mechanical concepts are considered and finally, a semiempirical method is extended to cover the relative Raman intensities of the external modes.