B. Krebs

Normal coordinate treatment of XY4-type molecules and ions with Td symmetry: Part I. Force constants of a modified valence force field and of the Urey-Bradley force field

Abstract Force constants of a modified valence force field and Urey-Bradley-Shimanouchi force constants are calculated for all XY 4 -type molecules and ions with T d symmetry for which reliable frequency data are known (except hydrides X H 4 ). Normal coordinates and the potential energy distribution are given for both potential models.

Normal coordinate treatment of XY4-type molecules and ions with Td symmetry: Part II. Force constants of a general valence force field (approximation method)

Abstract Force constants of the general valence force field are calculated according to an approximation method for all XY 4 -type molecules and ions with T d symmetry (except hydrides) for which reliable frequency data are known.

Crystal and molecular structure of creatininium tetrachlorocuprate(II)

Preparation, crystal and molecular structure of creatininium tetrachlorocuprate(II) is described. The structure was solved by X-ray diffraction studies and was refined by least-squares methods to R = 0.041 for 1344 reflections. The compound is monoclinic, space group, P2 1 /c. The unit cell parameters are a = 8.080(3), b = 7.831(2), c = 13.922(3) A, β = 113.77(2)°, V = 806.2 A 3 , d c = 1.786, d m = 1.77(1) g cm −3 , Z = 2. The [CuCl 4 ] 2− ion is centrosymmetric and the copper atom is surrounded by four Cl atoms (CuCl1 2.233(1), CuCl2 2.268(1)) in a square planar arrangement. The creatininium cation is almost planar and each cation is linked to [CuCl 4 ] 2− units through hydrogen bonding involving the amino and imino nitrogen atoms.

Die kristallstruktur des monoklinen hexamethylcyclotristannathians

Abstract A new monoclinic modification of hexamethyl cyclotristannathiane [(CH 3 ) 2 SnS] 3 was obtained by sublimation at 80°C/14 Torr of the crude product which is formed from the reaction of (CH 3 ) 2 SnCl 2 with Na 2 S in benzene. The phase (space group P 2 1 c , a = 7.409(3), b = 12.987(5), c = 19.346(7) A, β = 116.97(3)°, Z = 4) is stable at room temperature. The complete X-ray structure analysis shows the six-membered Sn 3 S 3 ring having a twist conformation (distorted boat form) similar to the conformation in tetragonal [(CH 3 ) 2 SnS] 3 . The SnS 2 C 2 tetrahedra are only slightly distorted. Mean bond distances are: SnS 2.411 (2.395 ··· 2.428(3)) A, SnC 2.127 (2.105 ··· 2.145(15)) A.

The crystal and molecular structure of tris(thiourea)silver(I) perchlorate

Abstract Tris(thiourea)silver(I) perchlorate, Ag[SC(NH2)2]3ClO4, is monoclinic with cell parameters a = 19.537(8), b = 13.436(6), c = 10.791(5) A, β = 103.57(5)°. The space group is C2/c with Z = 8, dc = 2.102 g. cm−3 and dm = 2.090 g.cm−3. The crystal structure was determined from three-dimensional diffractometer data and refined by least-squares methods with anisotropic thermal parameters to a conventional R factor of 0.048 for 2202 observed reflections. The structure is ionic and consists of binuclear complexes (Ag2[SC(NH2)2]6)2+ with C2 symmetry and perchlorate anions. The sulphur atoms of four thiourea molecules form a distorted coordination tetrahedron (SAgS angles range from 100.5(1) to 115.9 (1)°) around each Ag. Two of the six sulphur atoms of the binuclear complex cation act as bridging ligands in a four-membered AgSAgS ring (bridge bond lengths 2.663(2) and 2.684(2) A), the remaining four are terminal (AgS bond lengths 2.524(2) AND 2.570 (2) A). The bond angle AgSAg is 64.3(1), the Ag… Ag distance in the binuclear complex is 2.845(1) A. The bonding of the complex cation is different from the corresponding copper(I) complex. The orientation of the thiourea molecules suggests use of electron pairs of pπ sulphur-carbon MOs in the terminal as well as (together with sulphur sp2 orbitals) in the bridge AgS bonds.

Molekül- und kristallstruktur von hexamethylcyclo-tristannaselenan [(CH3)2SnSe]3

Hexamethylcyclotristannaselenane [(CH3)2SnSe]3 forms tetragonal crystals, space groups P41212, with a  986.5(2), c  1769.7(4) pm, Z  4. The complete X-ray structural analysis (two independent determinations) shows the six-membered ring to have a twist-boat conformation similar to [(CH3)2SnS]3. The SnSe2C2 tetrahedra are only slightly distorted, the mean bond distances being SnSe 253.1 (251.7⋯254.0(4)) pm, Sn C 2.13 (2.09⋯2.17(3)) pm. Conformational details are discussed.

Normalkoordinatenanalyse von ReO3N2−, ReO3S−, ReO3,Cl und ReO3Br

Abstract Force constants are calculated for compounds ReO 3 Z ( n −) (rhenium trioxide chloride, rhenium trioxide bromide, monothioperrhenate and nitridoperrhenate) using different potential models of the valence force system. The normal coordinates are given. It is found that the ReO stretching force constants increase with decreasing π bond order in the ReZ bonds. The position of the ReCl stretching frequency and the value of the stretching force constant in ReO 3 Cl are discussed.

Potentialverhältnisse in Oxiden und Oxoanionen (d 0-Konfiguration) des Typs XY4 mit Td -symmetrie

The Coriolis coupling coefficients of tetrahedral type XY4 transition metal oxides and anions with d 0 configuration of the central atoms which are calculated from M.V.F.F. and G.V.F.F. (method of Fadini) symmetry force constants show a general dependence on the mass ratio mX/mY. There is no such relation for the corresponding values obtained from Urey-Bradley force constants. Experimentally determined ζ constants for OsO4 and RuO4 agree well with the curves ζ=f (mX/mY) for the general and modified valence force fields and are very close to those estimated from the mass ratio alone. The investigation indicates that it is possible to estimate ζ values with simple methods and to use them to obtain possible ranges for force constants.

THE CRYSTAL AND MOLECULAR STRUCTURE OF THIOCYANATOBIS(THIOUREA)SILVER(I)

Abstract The crystal structure of Ag[SC(NH 2 ) 2 ] 2 SCN was determined from three-dimensional diffractometer data and refined by least-squares to a conventional R factor of 0.044 for 1642 observed reflections. The compound is monoclinic (space group C2 c ) with cell parameters a = 11.072(3), b = 13.838(4), c = 13.983(4) A, β = 111.65(3)°, Z =8, d c = 2.123 g cm −3 , d m = 2.11 g cm −3 . Within one complex Ag(tu) 2 SCN unit, three S atoms of two thiourea molecules (AgS 2.482(2) and 2.462(2) A) and of one SCN group (AgS 2.608(2) A) are bonded to the central Ag with almost trigonal planar AgS 3 coordination. One of the two thiourea S atoms is weakly coordinated to a second Ag center (AgS 3.111(2) A), forming a dimeric complex [Ag (tu) 2 SCN] 2 unit with C i symmetry and with a central planar four-membered AgSAgS ring (Ag⋯Ag 3.097(1) A, bond angles SAgS 113.9(1)° and AgSAg 66.1(1)°). The orientation of the bridging thiourea molecule suggests the contribution of electron pairs in pπ carbon-sulfur MOs besides those in sulfur sp 2 orbitals to the AgS bonding system, all bridge bonds being two-electron two-center bonds.

Schwingungsspektren und Kraftkonstanten des Tetraselenomolybdats(VI) und des Tetraselenowolframats(VI). Raman-Spektren von (NH4)2MoO2S2 und (NH4)2WO2S2

Abstract Infrared and Laser Raman spectra of MoSe 4 2− (colour: deep violet) and WSe 4 2− (deep red) were recorded. The results of a normal co-ordinate analysis on these ions is given. Furthermore, the unknown Raman spectra of (NH 4 ) 2 MoO 2 S 2 and (NH 4 ) 2 WO 2 S 2 a more complete Raman spectrum of (NH 4 ) 2 MoS 4 than those previously recorded are reported and discussed.