A. Vegas

Crystal structure of 4-phenyl-1,2-dithia-3,5-diazole dimer

4-Phenyl-1,2-dithia-3,5-diazolium chloride on reduction with thiocyanate ion gives the black air-sensitive title compound, (PhCN2S2)2. Crystals have been studied by means of X-ray diffraction at room temperature. The compound crystallizes in the space group P212121(no. 19) with a= 16.061(1), b= 32.984(5), and c= 5.774 0(4)A, and Z= 8. The crystal structure has been solved using 2 513 reflections and refined to a final R value of 0.082. Each asymmetric unit contains two (PhCN2S2)2 molecules. Within each dimer the bridging mean S ⋯ S distance is 310.9(5)pm. The two half-molecules within each dimer are nearly parallel and are slightly twisted with respect to each other. The short (mean) CN2S2 ring distances (dCN= 133, dSN= 162, dSS= 209 pm) and the PhCN2S2 coplanarity suggest that the rings are aromatic with one electron pair delocalized at the four (disulphide) sulphur atoms.

The crystal structure of calcium orthoborate: a redetermination

reflexions to the data sets, as in the case of K3[Co(CN)6], is not possible. The implication of these results is that the partial symmetry operations of the OD groupoid symbol are to be regarded as approximate rather than exact and that the degree to which they are obeyed varies from structure to structure, f)urovi6 (1974) has suggested that the more ordered the crystal, the less it complies with the ideal OD model. Although this is consistent with K3[Cr(CN)6], which exhibited well-defined maxima on exceedingly weak streaks, it is by no means consistent with Ka[VO(CN)s] for which the streaks were more or less continuous and without well-defined maxima. Similarly, it would seem somewhat difficult to reconcile this suggestion with preliminary results from the refinement of diaquobis(salicylato)copper(II) (Jagner, Hazell & Larsen, 1975) which indicate that the partial symmetry operations are preserved more exactly in the monoclinic MDO2 structure than in the orthorhombic MDO1 structure, both structures having been solved from the same crystal. Obviously, more evidence is needed before the extent to which the partial symmetry operations relax can be classified and suitably interpreted. From a practical point of view, since it is usually necessary to impose some sort of constraint, at least during the initial stages of refinement, in order to obtain convergence, it would seem more appropriate to preserve the partial symmetry operations of the OD groupoid symbol, even if these constraints are later released, than to more or less arbitrarily select one or more parameters to be fixed. In those cases where there is little difference between the constrained and unconstrained models, constrained refinement does, of course, yield bond distances and angles with smaller standard deviations.

High-pressure experimental study on Rb2S: antifluorite to Ni2In-type phase transitions.

The high-pressure behaviour of dirubidium sulfide, Rb(2)S, with antifluorite-type structure under room conditions (space group Fm ̄3m) has been studied up to 8 GPa at room temperature using angle-dispersive X-ray powder diffraction in a diamond-anvil cell (DAC). X-ray measurements have allowed us to completely characterize two phase transitions upon compression: (i) to an anticotunnite-type structure (Pnma) at some pressure between 1 bar and 0.7 GPa, and (ii) to a Ni(2)In-type structure (P6(3)/mmc) at 2.6 GPa. A gradual transition from the Pnma to the P6(3)/mmc structures seems to occur between 2.6 and 4.5 GPa. These results are in excellent agreement with previous theoretical predictions. Strong luminescence is observed above 2.6 GPa (band maximum at 703 nm) when the transition to the Ni(2)In-type phase starts to occur, the band maximum showing a non-linear blue shift with pressure. The observed sequence of phase transitions in Rb(2)S is discussed in relation to the high-pressure structural behaviour of isomorphic sulfides and the structures are compared with the cationic arrays of their corresponding oxides (e.g. rubidium sulfate, in which the sulfide has been oxidized).

Synthesis and reactivity of hydroxo-bridged binuclear platinum complexes. Crystal structure of [NBu4]2[{Pt(C6F5)2(µ-OH)}2]

The reaction of [NBu4]2[{Pt(C6X5)2(µ-Cl)}2] with NBu4OH(aq) in acetone leads to the formation of the hydroxo-complexes [NBu4]2[{Pt(C6X5)2(µ-OH)}2](X = F 1 or Cl 2). These react with weak protic acids such as acetylacetone (Hacac), benzoylacetone (Hbzac) and 8-hydroxyquinoline (Hquin) yielding the mononuclear complexes [NBu4][Pt(C6X5)2(L–L)](X = F, L–L = acac 3, bzac 4, or quin 5; X = Cl, L–L = acac 6, bzac 7, or quin 8). Treatment of complexes 1 and 2 with PhCN in the presence of HBF4 gives the mononuclear compounds cis-[Pt(C6X5)2(PhCN)2](X = F 9 or Cl 10). When the benzonitrile complexes are treated with aniline the corresponding cis-[Pt(C6X5)(NH2Ph)2](X = F 11 or Cl 12) are formed. The benzamido derivatives [NBu4][Pt(C6X5)2(HNOCPh)(H2O)](X = F 13 or Cl 14) are formed when complexes 9 and 10 are treated with NBu4OH(aq) in acetone, and thermal treatment of 13 yields [NBu4]2[{Pt(C6F5)2(µ-HNOCPh)}2]15. Complexes 9 and 10 react with methanol in the presence of NBu4OH to give the corresponding imido ester derivatives [Pt(C6X5)2{HNC(OMe)Ph}2](X = F 16 or Cl 17). Spectroscopic (IR, 1H and 19F) data have been used for structural assignments, and an X-ray structure determination carried out for [NBu4]2[{Pt(C6F5)2(µ-OH)}2] has established the centrosymmetric binuclear nature of the anion [(C6F5)2Pt(µ-OH)2Pt(C6F5)2]2–. The structure has been solved and refined up to R= 0.049 and R′= 0.056 based on 2278 observed reflections. The Pt atoms are four-co-ordinated and show slight deviations from a square-planar arrangement.

Reactions of cationic hydrido complexes [Ru(CO)H(MeCN)2(PPh3)2]A (A ClO4, PF6) with alkynes. The crystal structure of [Ru(CO) (MeOOCCCHCOOMe) (MeCN)2(PPh3)2]ClO4

Abstract Reactions of [Ru(CO)H(MeCN)2(PPh3)2]A with mono- and di-substituted acetylenes give the alkenyl derivatives [Ru(CO)(RCCHR′)(MeCN)2(PPh3)2]A (A  ClO4, R  H; R′  C3H7, CMe3, Ph, COOMe; R  R′  COOMe; A  PF6, R  R′  Ph) resulting from a cis-insertion of the alkyne into the RuH bond. The reaction of the perchlorate complex with diphenylacetylene yields alkenyl chlororuthenium derivatives resulting from the unexpected reduction of the perchlorate anion to chloride. The crystal structure of [Ru(CO)(MeOOCCCHCOOMe)(MeCN)2(PPh3)2]ClO4 has been determined by X-ray crystallography (orthorhombic, P212121, a 14.498(1), b 15.080(1), c 22.677(2) A). In this cationic complex both phosphine and acetonitrile molecules and, consequently, the carbonyl and alkenyl ligands are mutually trans, whereas in the other complexes only the phosphine ligands are in trans disposition, as inferred from 1H NMR spectroscopic data.

The Zintl-Klemm concept applied to cations in oxides. I. The structures of ternary aluminates.

The structures of 94 ternary aluminates are reinterpreted on the basis of the Zintl-Klemm concept and Pearsons generalized octet rule. In aluminates of highly electropositive metals such as alkali, alkaline-earth and rare-earth metals, the Al atoms form three-dimensional skeleta which can be interpreted as if the Al atoms were behaving as Zintl polyanions, adopting the structure of either main-group elements or Zintl polyanions showing the same connectivity. The O atoms are then located close to both the hypothetical two-electron bonds and the lone pairs, giving rise to a tetrahedral coordination. When more electronegative elements, such as W or Si, are present in the compound, the electron transfer towards the Al atoms does not take place. In this case, aluminium behaves as a base, transferring its electrons to the more electronegative atoms and the coordination sphere of aluminium becomes octahedral. In some compounds the Al atoms clearly show amphoteric character so that some Al atoms act as donors (bases) and hence are octahedrally coordinated, whereas others behave as acceptors (acids), adopting a tetrahedral coordination. From this it is concluded that the coordination sphere of aluminium is not a function of the ionic radius of the Al(3+) cations, but it depends on the nature of the other cations accompanying them in the structure. The networks formed by these aluminates are, in many instances, similar to those of the binary oxides of the main-group elements. For this reason, a systematic survey of these oxides is also reported. Compounds such as stuffed cristobalites and trydimites and also perovskites are examples of this new interpretation. Perovskites are then reinterpreted as a stuffed pseudo-TeO(3) structure. Other families of compounds such as silicates and phosphates are susceptible to a similar interpretation. This study provides additional examples of how cations recognize themselves in spite of being embedded in an oxygen matrix.

Cationic rhodium tetrafluorobenzobarrelene complexes with diolefin or arene ligands, crystal structures of [Rh(TFB)(arene)] ClO4, (arene = C6Me6, C6H3Me3, C6H4Me2)

Abstract The preparation and properties of complexes of the general formulae [Rh(TFB)(diolefin)]ClO4, [Rh(TFB)(arene)]ClO4 and [Rh(TFB)L2]ClO4, (TFB = tetrafluorobenzobarrelene, L = dimethylsulfoxide and tetrahydrothiophen) are described. The crystal structures of the arene complexes (arene = C6Me6, C6H3Me3 and C6H4Me2) have been solved by X-ray methods. The three compounds crystallize in quite similar lattices: R3c, a = b = 27.122, 26.233, 25.731 and c = 17.079, 16.388, 16.256 A, respectively. δR-plots for about 2000 reflections show the agreement in the refinements carried out up to R-values of 5%, 5% and 4% respectively. The Rh atom is coordinated to the double bonds of the TFB and to the arene ring in all three compounds, but the deviation from planarity of the arene and its relative position with respect to the TFB moiety varies.

Crystal structure of 3Bi2O3:5B2O3. A new type of polyborate anion (B5O11)7−

Single crystals of 3Bi2O3:5B2O3 have been obtained from the melt and subsequent devitrification of the glassy compound, at 450°C during 90 hr. The compound is orthorhombic, space group Pnma with two formula units in the cell. The lattice parameters are a = 6.532 A, b = 7.733 A, c = 18.566 A. The structure was solved from a complete set of three-dimensional MoKα diffractometer data, the final R being 0.097. The structure is made up of Bi3+ cations and O2− and (B5O11)7− anions. The pentaborate anion is formed by two BO4 tetrahedra and three BO3 triangles, sharing edges and corners. An oxygen that is not bonded to any boron is in the center of a three-bismuth triangle. Two independent bismuth atoms are present in the structure. Bi(1) has six first-neighbor oxygens with an average BiO distance of 2.44 A and Bi(2) has either six or seven oxygens in the first coordination sphere with an average BiO distance of 2.43 or 2.80 A, respectively.

Structural stability of Fe5Si3 and Ni2Si studied by high-pressure x-ray diffraction and ab initio total-energy calculations

We performed high-pressure angle dispersive x-ray diffraction measurements on

Pseudoatoms and preferred skeletons in crystals

{\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}