Geoffrey A. Williams

Synthesis and structure of bis(diethyldithiocarbamato)nitridotechnetium(V): a technetium–nitrogen triple bond

The title compound [Tc(S2CNEt2)2N] has been prepared by the reduction of [NH4][TcO4] with hydrazine followed by reaction with Na[S2CNEt2]. The crystal structure of [Tc(S2CNEt2)2N] has been determined by single-crystal X-ray diffraction methods at 17 °C. Crystals are monoclinic, space group P21/c, with a= 14.823(1), b= 9.159(1), c= 12.865(1)A, β= 107.98(1)°, and Z= 4. Diffractometry has provided significant Bragg intensities for 2 152 independent reflections and the structure has been refined by full-matrix least-squares methods to R 0.042. The compound, which is isostructural with the rhenium analogue, consists of discrete [Tc(S2CNEt2)2N] molecules, each containing a terminal N3– group. The technetium atom has a distorted square-pyramidal environment with the nitrogen atom in the apical position and four sulphur atoms forming the base. The TcN bond, which has not been observed before, has a length of 1.604(6)A, and the Tc–S bond distances range between 2.392(2) and 2.405(2)A.

Electrically Controllable Liquid Crystal Fresnel Lens

Two orthogonally aligned liquid crystal lenses with spherical Fresnel zone plate electrode configurations have been demonstrated to focus an unpolarised broadband object with resulting good quality images. Switch on times of 15ms are reported along with modulation depths of 91.5%.

Preparation of the technetium(VI) aquanitrido complexes (NEt4)[TcNX4(OH2)] (X= Cl or Br). Crystal structures of (NEt4)[TcNBr4(OH2)] and Cs2[TcNCl5]

Addition of NEt 4 X to a conc. HX solution of [TcNX 4 (OH 2 )] − (X= Cl or Br) yields crystals of (NEt 4 )[TcNX 4 (OH 2 )] (X=Cl ( 1 ) or Br ( 2 )). Complex 2 crystallises in the orthorhombic space group Pnma with a = 11.366(1), b = 12.930(2), c = 11.540(1) A and Z = 4. Refinement with 1434 data measured with Cu K α radiation converged with R = 0.047. The complex anion has distorted octahedral geometry with a water molecule trans to the nitrido ligand (TcN 1.599(9) and TcOH 2 2.443(7) A). Crystals of Cs 2 [TcNCl 5 ] ( 3 ) belong to the cubic space group Fm m with a = 10.211(1) A and Z = 4. The ligands of the complex anion are statistically disordered over six octahedral sites as required by the cubic space group. Refinement based on 78 data measured with Cu Kα radiation, and with a fixed TcN distance of 1.6 A, converged with R = 0.034. In this model Tc is displaced 0.401(3) A from the plane of the cis ligands towards the nitrido ligand with TcCl cis = 2.373(5), TcCl tras = 2.740(5) A.

Structural chemistry of phthalocyaninato-cobalt(II) and -manganese(II)

The crystal and molecular structures of the β-polymorphic forms of phthalocyaninatomanganese(II), [Mn(pc)], and phthalocyaninatocobalt(II), [Co(pc)], have been determined by single-crystal X-ray diffraction methods at 295 K, and also at 116 K in the case of [Mn(pc)]. Crystals are of the monoclinic β-polymorph type, space group P21/c, Z= 2; for [Mn(pc)](116 K), a= 14.590(3), b= 4.741(1), c= 19.301(5)A, β= 120.79(1)°; (295 K), a= 14.576(5), b= 4.755(1), c= 19.362(7)A, β= 120.70(2)°; [Co(pc)](295 K), a= 14.542(2), b= 4.773 1(5), c= 19.352(2)A, β= 120.824(7)°. Automatic diffractometry has provided significant Bragg intensities for 1 608 {[Mn(pc)], 116 K}, 1 525 (295 K), and 1 930 {[Co(pc)]} independent reflections and the structures have been refined by full-matrix least-squares methods to R 0.038 {[Mn(pc)], 116 K}, 0.072 (295 K), and 0.039 {[Co(pc)]}. The metal atoms co-ordinate within the central cavity of the macrocyclic phthalocyaninate ligand to a precisely planar array of nitrogen atoms, with mean bond lengths Mn–N = 1.941(3)A at 116 K, 1.933(5)A at 295 K, and Co–N 1.908(2)A. The intermolecular packing is of the typical herringbone arrangement, with angles of 47.9 {[Mn(pc)], 116 K} and 47.3°{[Co(pc)]} between the normals to the MN4 co-ordination planes and the crystallographic b axes. Each molecule has close contacts with two neighbours related by translations of ±b, resulting in pseudo-octahedral metal environments with axial Mn–N contacts of 3.150(3)(116), 3.169(6)A(295 K), and a Co–N contact of 3.219(3)A. The importance of these intermolecular contacts in establishing a ferromagnetic exchange path in [Mn(pc)] is discussed, as are deviations within the macrocyclic ligand from D4h symmetry.

Spin Density and Bonding in the CoCl

We report improvement in the precision of certain of the polarized neutron diffraction data for Cs3CoCl5. The improvement allows us to analyse the data using a chemically based model of the spin-density distribution that is equivalent to a conventional multipole treatment to fourth order on the cobalt, and to second order on the chlorine atoms of the CoCl2–4 ion. To test the completeness of the model and to understand the meaning of the parameters in terms of the wavefunction, we have used it to analyse a set of theoretical magnetic structure factors. These are obtained from the wave-function of a Hartree–Fock calculation on the CoCl2–4 ion. We obtain an excellent fit to the theoretical ‘data’ and a much improved fit to the experimental data when the new model is used. We confirm the main features of the spin- and charge-density distributions deduced in our previous study, and we are now also able to interpret the experimental parameters in terms of the wavefunction by analogy with the fit to the theoretical data. We find that there is ca. 3 % of the total spin delocalized onto each chlorine atom of the CoCl2–4 ion, dominantly via σ - rather than π-bonding. There is a well defined diffuse spin density on the cobalt atom of 4p symmetry, and strong evidence for 3d–4p mixing. The spin density, in this almost cubic ion, has distinct non-cubic symmetry, which may arise from longer-range effects due to the rest of the tetragonal crystal.

^{2-}_4

Magnetostructural correlations have been made on a matched pair of O-bridged (phenolato) and S-bridged (thiophenolato) binuclear copper(II) complexes of type [Cu2(L-X)(pz)], where L-O and L-S are 2,6-bis(4′-cyclohexyl-4′-hydroxy-2′,3′-diazabuta-1′,3′-dien-1′-yl)-4-methyl-phenolat(3–) and -thiophenolate(3–) respectively and pz is an exogenous bridging pyrazolyl ligand. The crystal structure of [Cu2(L-S)(pz)(CH3OH)] is the first structure reported for a binuclear copper(II) complex containing a thiophenolato bridging group within a binucleating ligand framework. Crystals are monoclinic, space group P21/c, with a= 15.887(5), b= 12.714(4), c= 29.178(6)A, β= 91.81(2)°, T= 23 ± 1 °C, and Z= 8. Crystals were generally of poor quality and it was only with difficulty that a suitable crystal for intensity data collection was obtained. Automatic diffractometry provided Bragg intensities for 4 594 independent reflections and the structure has been refined by least-squares methods to R 0.163 (all data) and 0.086 [I > 2σ(I)]. The structure consists of two crystallographically unique but chemically similar binuclear molecules in the asymmetric unit, each with one four-co-ordinate and one five-co-ordinate copper atom bridged by a thiophenolate-sulphur atom of the binucleating ligand and by a pyrazolyl group. The Cu ⋯ Cu separations are 3.474(3) and 3.424(3)A in the two molecules, with Cu–S–Cu angles of 101.5(2) and 99.5(2)° respectively. The angles around the S atom are compatible with a pyramidal (sp3) disposition of bonds which contrasts with the (presumed) trigonal-planar (sp2) bonding of the phenolato O atom in [Cu2(L-O)(pz)]. Variable-temperature magnetic susceptibility measurements have shown that the antiferromagnetic coupling in [Cu2(L-S)(pz)] is much weaker (2J=–5.2 cm–1) than in [Cu2(L-O)(pz)](2J=–382 cm–1). In a related S-bridged complex possessing different side groups attached to the thiophenolate ring, the coupling is weakly ferromagnetic. These differences in exchange coupling can be related to geometric differences in the Cu2(L-X) bridging moiety.

Ion in Cs

Langmuir-Blodgett (LB) films of 1-tert-butyl-1,9-dihydrofullerene-60 are shown to undergo well defined multistage electrochemical reductions to yield the trianion species, with the first two redox waves stable to recycling; these data contrast with those for LB films of the parent system C60.

_3

The title compound, [TcN(NCS)2(CH3CN)(PPh3)2]·0.5CH3CN, has been prepared by substitution of [TcNCl2(PPh3)2] with NH4NCS followed by the reaction of the [TcN(NCS)2(PPh3)2] complex with CH3CN. The crystal structure of [TcN(NCS)2(CH3CN)(PPh3)2]·0.5CH3CN has been determined by single-crystal X-ray diffraction methods at 25 ± 2 °C. Crystals are monoclinic, space group P21/c, with a= 9.296(3), b= 18.614(5), c= 23.307(6)A, β= 109.63(2)°, and Z= 4. Diffractometry has provided significant Bragg intensities for 5 498 independent reflections and the structure has been refined by full-matrix least-squares methods to R= 0.045. The compound consists of discrete [TcN(NCS)2(CH3CN)(PPh3)2] molecules with CH3CN of crystallisation also present in the crystal lattice. The technetium atom has a distorted octahedral environment with Tc–N–C angles of 177.1 (4) and 166.7(4)° for the NCS ligands and 168.6(4)° for the CH3CN ligand. The TcN bond distance is 1.629(4)A and the strong trans influence of the nitrido-group is evident in the exceptionally long Tc–N bond distance [2.491 (4)A] to the CH3CN ligand.

CoCl

The spin density distribution in the metal–ligand framework of the title compound has been determined from two-dimensional polarised neutron diffraction data. A qualitative picture of the superexchange pathway between copper atoms in the dimeric molecule emerges, and the importance of spin polarisation effects is indicated by the presence of significant regions of negative spin density on the sides of the bridging oxygen atoms away from the copper atoms. The important role played by the spin polarisation phenomenon in the exchange process indicates the need for a full unconstrained Hartree–Fock calculation in any theoretical treatment of the CuO2Cu system. As a necessary corollary to the spin density study, the molecular structure of [(H2O)(bipy)Cu(OH)2Cu(bipy)(OSO3)]·4H2O (bipy = 2,2′-bipyridine) has been determined at 4.2 K by single-crystal neutron diffraction methods from limited three-dimensional intensity data. Crystals are monoclinic, space group P21/c, with a= 9.658(12), b= 34.29(3), c= 7.626(10)A, β= 103.3(1)°, and Z= 4.

_5

The use of formamidine sulphinic acid as a reducing agent in the presence of technetium-99-pertechnetate and diethyldithiocarbamate ligand has been shown to yield a complex containing a Tc=CO bond. The carbon monoxide present in this complex originates from the reducing agent itself. Evidence is presented which suggests that this carbonyl complex is present in the 99mTc-diethyldithiocarbamate preparation obtained by the use of formamidine sulphinic acid as the reducing agent. Use of hydrazine as a reducing agent yields a complex containing a Tc ≡ N bond. It is apparent that when reducing agents such as hydrazine or formamidine sulphinic acid are used in the preparation of 99mTc-radiopharmaceuticals, the possibility of the formation of complexes structurally different to those obtained by the use of stannous chloride must be considered.