Tsun K. Sham

Additive model for 119Sn Mössbauer quadrupole splitting in five-co-ordinate organotin(IV) compounds

Mossbauer parameters are reported for ten cationic organotin(IV) complexes of type [R3SnL2][BPh4](R = alkyl or phenyl, L = electrongegative ligand). Details are given of a regression method which is used to distinguish structural isomers of trigonal-bipyramidal [R3SnL2] species by their 119Sn quadrupole splittings. By use of new and literature data, partial quadrupole splitting (p.q.s.) parameters are calculated for a variety of ligands in trigonal-bipyramidal structures. Comparison of theory with experiment indicates that the additive model gives a consistent account of the relationship between quadrupole splitting and stereochemistry in trigonal-bipyramidal organotin(IV) compounds. The 119Sn parameters are used to calculate p.q.s. parameters for 121SbV, thus extending recent work on application of the additive model to five-co-ordinate organoantimony(V) compounds.

Preparation and spectroscopic studies of five-co-ordinate β-diketonatotri(organo)tin compounds. Crystal structure of (1,3-diphenylpropane-1,3-dionato)triphenyltin(IV)

A series of new five-co-ordinate complexes, R3SnL [R = Me. (I)–(III) or Ph, (IV)–(VI); L = anions of acetylacetone (acac), benzoylacetone (bzac), or dibenzoylmethane (bzbz)], has been prepared and characterized by i.r., n.m.r. and Mossbauer spectroscopy. Compounds (I)–(III) have large quadrupole splittings (3·69–3·86 mm s–1), while those of (IV)–(VI) are much smaller (1·38–2·25 mm s–1). By use of partial quadrupole splittings these splittings are shown to be consistent with the mer-structure for compounds (I)–(III), and the all-cis-structure for (IV)–(VI). The all-cis-structure has been confirmed for (VI), [Ph3Sn(bzbz)], by a single-crystal X-ray diffraction study. Crystals are monoclinic, space group P21/c, with Z= 4 in a unit cell of dimensions: a= 13·216(5), b= 9·443(4), c= 22·344(9)A, and β= 109·42(2)°. The structure was solved by the heavy-atom method from intensity data collected by diffractometric methods, and refined by full-matrix least-squares methods to R 0·051 for 2328 observed reflections. The co-ordination about the Sn atom is essentially a distorted trigonal bipyramid. The phenyl groups occupy one axial and two equatorial co-ordination sites with the chelating ligand bonded to one equatorial and one axial site. Sn–C(eq) Bond lengths are 2·149(7) and 2·181(6), and Sn–C(ax) 2·180(6)A. The Sn–O(ax) distance [2·276(7)A] is significantly longer than Sn–O(eq)[2·094(7)A].

Linewidths and line shapes in solid state ESCA studies: Electric field gradient broadening of Sn 3d lines

Abstract ESCA Sn 3d linewidths of nonconducting organometallic tin solids, prepared by in situ evaporation, are within about 10% of the values for analogous gas phase measurements. The similar line shapes (≈ 35% gaussian, 65% lorentzian) observed for solid state and gas phase spectra show that effects which give increasing gaussian components, such as charge broadening and phonon broadening, are very small in our solid state spectra. The general correlation between ESCA Sn 3d linewidths and Mossbauer quadrupole splittings indicates that electric field gradient splitting of the Sn 3d lines approaches ≈ 0.4 eV.

Configuration interaction satellites in the ESCA spectra of thorium and other actinide compounds

Abstract ESCA spectra of the Th 4d, 4f, 5s, 5p and 5d core levels have been recorded in ThF4, Th(AcAc)4 and other Th complexes. In addition to weak 4f and 5d satellites which are normally considered to be shake up satellites, a number of unusual satellites have been characterized in these compounds. In particular, the intense 5p3/2 satellites, as well as previous similar 5p 3 2 satellites in other actinides, are shown to be due to configuration interaction of the 5p hole state with a 5d2 hole state. Similarly, the 4d 5 2 , 5s and additional 5d satellites are probably also due to configuration interaction.

An ESCA study of Sn organometallic compounds: Solid state broadening effects

Abstract X-ray photoelectron spectra have been recorded for a number of solid and gaseous organotin compounds. Solid-state charging effects (such as differential charge broadening) can be large, though we have almost eliminated them by subliming very thin films onto platinum metal. In this way, we have obtained solid-state Sn 3d line widths that are within 10% of the analogous gas-phase values. The quality and reproducibility of the solid-state spectra likewise approach those of gases. The general correlation between ESCA Sn 3d line widths and Mossbauer quadrupole splittings indicates that the broadening of the Sn 3d lines is due to crystal-field splitting from the C 2 0 term (the quadrupole term) in the crystal-field expansion. There is a general correlation between ESCA binding energies and Mossbauer isomer shifts for the solids.

Shake-up satellites in x-ray photoelectron (ESCA) spectra of 5f0 Th(IV) compounds

Abstract X-ray photoelectron (ESCA) spectra of the Th 4f levels have been recorded in 12 Th compounds. Weak satellites are observed in all the 4f spectra at binding energies 4–6 eV from the primary photolines. On the basis of a multiple scattering calculation in ThO 2 , these satellites are assigned to ligand (e.g. O 2p) to Th 5f shake-up transitions. As with La 3d satellites, the satellite intensities correlate well with the nephelauxetic order of ligands.

An additive treatment of 115In nuclear quadrupole coupling constants for organoindium compounds

Abstract Using previously measured 119SnIV and 115InIII e2Qq values, we use the additivity model to rationalize and calculate 115In e2Qq values for InIII in a variety of coordination environments. A semiquantitative estimate of InIII e2Qq values (in MHz) may be obtained by multiplying the 1 2 s 2 Qq value (in mm sec−1) for the isostructural SnIV compound by 310. Absolute partial quadrupole coupling constants (pqcc) have been derived for the first time for linear (sp hybridized metal) and trigonal planar (sp2 hybridized metal) species. The ratios of the pqcc values (pqcc)Metet:(pqcc)Metba: (pqcc)Meoct is 1.23:1.09:1. These are in good agreement with the corresponding 119Sn partial quadrupole splitting (pqs) values. The relative pqce values for ligands in two to six coordination are in qualitative agreement with those expected from a simple molecular orbital approach. The pqcc parameters are used to calculate the expected e2Qq values for a number of methylindium species in four, five, and six coordination. These calculations should be very useful for structural elucidation. For the associated compounds MeInBr2 and EtInI2, these calculations suggest highly associated structures with In having a coordination number of greater than four. For the six coordinate Me2In moieties, the trend in e2Qq with C-In-C angle is reproduced qualitatively by a simple distortion calculation.

Ferric/ferrous-iron ratios in bulk rock samples by Mössbauer spectroscopy — The determination of standard rock samples G-2, GA, W-1 and mica-Fe

Abstract Room-temperature 57Fe Mossbauer spectra have been recorded for the USGS rock-standards G-2 and W-1; the CRPG standards GA and mica-Fe; and an “in-house” standard, NS. A comparison of the results of ferric/ferrous-Fe ratios by chemical and Mossbauer analysis is presented. The errors involved in each method are assessed. In the low-Fe rocks, chemical analysis appears to considerably over-estimate ferric content although the spread of individual laboratory values tend to a low limit close to the Mossbauer values.

Structure of five-co-ordinate SnIV isomers from Mössbauer quadrupole splittings

The three isomers of trigonal bipyramidal R3SnL2 have been distinguished by linear regression analysis of new 119Sn quadrupole splitting data for five-co-ordinate R3SnL2 and six-co-ordinate R2SnL4 species, showing that the five-co-ordinate systems have splittings ranging from ca. 1.7–2.3 mm s–1 for cis-R3SnL2, ca. 3.0–3.9 mm s–1 for equatorial-R3SnL2, and ca. 3.5–4.1 mm s–1 for mer-R3SnL2.

Synthesis and Mössbauer spectra of six-co-ordinate tin–metal compounds: quotient of the partial quadrupole splittings of the six- and four-co-ordinate species

Nine new six-co-ordinate tin(IV) compounds have been prepared of the type [M(SnCl3L)][M = Mn(CO)5, Mn(CO)4(PPh3), Fe(cp)(CO)2; L = phen or bipy], [M(SnXL′2)](X = Cl or Ph; L′= quin or pd), and [M{SnPhCl2(phen)}]. Structures for these and other similar compounds have been assigned using carbonyl i.r. stretching frequencies and 119Sn Mossbauer quadrupole splittings. Partial quadrupole splittings for six-co-ordinate species, (p.q.s.)Loct, have been calculated from these quadrupole splittings. There is an excellent linear corrleation (R 0.991) between the (p.q.s.)Loct values and previously calculated (p.q.s.)Ltet values: (p.q.s.)Loct= 0.73(p.q.s)Ltet–0.01. The gradient of 0.73 is compared with that (0.67) calculated previously from molecular-orbital arguments. The relative bonding characteristics for the M groups in six-co-ordination are the same as those evaluated for M groups in four-co-ordinate compounds. Thus, the order of p-donor strength in six-co-ordination is Mo(cp)(CO)3 < Mn(CO)5 < Mn(CO)4(PPh3)≈ Fe(cp)(CO)2 < Ph < Me, while the M–Sn bonds have substantially higher Sn 5s character than Me or Ph–Sn bonds.