Transition-metal(II) thiocyanate coordination compounds containing 4-allyl-1,2,4-triazole. Structure and magnetic properties.

The synthesis and characterisation of a series of dinuclear and polynuclear coordination compounds with 4-allyl-1,2,4-triazole are described. Dinuclear compounds were obtained for Mn(II) and Fe(II) with composition [M₂(Altrz)₅(NCS)₄], and for Co(II) and Ni(II) with composition [M₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂. The crystal structure of [Co₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂ was solved at room temperature. It crystallizes in the monoclinic space group P2₁/n. The lattice constants are a = 18.033(3) Å, b = 13.611(2) Å, c = 15.619(3) Å, β = 92.04(2)° Z = 4. One cobalt ion has an octahedrally arranged donor set of ligands consisting of three vicinal nitrogens of 1,2-bridging triazoles (CoN = 2.14–2.15 Å), one terminal triazole nitrogen (CoN = 2.12 Å) and two N-bonded NCS anions (CON = 2.08 Å). The other Co(II) ion has the same geometry, but the terminal triazole ligand is replaced by H₂O (CoO = 2.15 Å). The crystal structure is stabilised by hydrogen bonding through H₂O molecules, S-atoms of the NCS anions and the lone-pair electron of the monodentate triazole. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J-values of ?0.4 cm^?1, ?10.9 cm^?1 and ?8.7 cm^?1 respectively. The Co compound was interpreted in terms of an Ising model. For [Zn₂(Altrz)₅(NCS)₂]∞[Zn(NCS)₄], [Cu₂(Altrz)₃(NCS)₄]∞ and [Cd₂(Altrz)₃(NCS)₄]∞ chain structures are proposed. In the Cu compound thiocyanates appear to be present, bridging via the nitrogen atom, as deduced from the IR spectrum.     

N,N-diisopropylcarboxylic acid amide complexes of thorium(IV) and uranium(IV) N-thiocyanates; the crystal structure of tetraisothiocyanato tetrakis(N,N-diisopropylacetamide-O)uranium(IV)

The complexes M(NCS)₄·xL (x = 2, M = U, L = Me₃CCON(Prⁱ)₂(dippva); x = 3, M = Th, L = Me₂CHCON(Prⁱ)₂(dipiba) and dippva, M = U, L = EtCON(Pr¹)₂(dippa), dipiba and dippva; x = 4, M = Th, L = MeCON(Prⁱ)₂(dipa), dippa and dipiba, M = U, L = dipa, dippa) and the solvates M(NCS)₄·4dipa·CH₂Cl₂ (M = Th, U) have been prepared. Their i.r. and u.v.-visible (M = U only) spectra are reported. The crystal and molecular structure of U(NCS)₄(dipa)₄· CH₂Cl₂ has been determined by the heavy-atom method from X-ray diffractometer data and refined by least squares to R 0.029 for 1135 independent reflections. The crystal is tetragonal, space group P$\text{4}$2₁c, with Z = 2, a = 15.663(4) and c = 10.512(3) Å. The coordination geometry about the 8-coordinate uranium atom is dodecahedral with the N atoms of the NCS groups occupying the dodecahedral A sites and the ‘dipa’ O atoms the B sites. The bonding distances of UO and UN are 2.363(8), and 2.444(11) Å respectively.     

Structural chemistry of actinide compounds with different coordination numbers: The crystal and molecular structures of tetrachlorotris(N,N-diethylpropionamide)thorium(IV) and tetra-N-thiocyanato tetrakis(N,N-dimethylpropionamide)thorium(IV)

The crystal and molecular structures of ThCl₄(depa)₃ (1) (depa = N,N-diethylpropionamide) and Th(NCS)₄(dmpa)₄ (2) (dmpa = N,N-dimethylpropionamide) have been determined from three-dimensional X-ray diffraction data. The compounds crystallize in space group P2₁/n (1) and P2₁/a (2), with a = 18.107(5), b = 10.347(3), c = 17.867(5) Å, β = 108.5(1)°, Z = 4 (1) and a = 22.759(6), b = 13.763(4), c = 11.910(3) Å, β = 91.4(1)° and Z = 4 (2). Full matrix least-squares refinement of both structures gave for (1) with 3126 intensity data R = 0.046 and Rw 0.046 and for (2) with 3480 intensity data R = 0.050, Rw 0.054. The different steric constraints imposed by the ligand give rise to different coordination numbers. In (1) the coordination polyhedron about the seven co-ordinate thorium atom is a pentagonal bipyramid with two chlorine atoms in the axial positions, an unusual geometry for Th(IV) species. The average bonding distances are ThO = 2.340(9), ThCl_eq = 2.754(3) and ThCl_ax = 2.692(3) Å.In (2) the less hindering dmpa ligand favours the presence of four of them in the metal coordination sphere in a distorted square antiprismatic coordination geometry. ThO and ThN average 2.37(1) and 2.49(2) Å respectively.     

Organocobalt B12 Models. Structures of trans-bis(glyoximato)(alkyl)(pyridine)cobalt(III), with Alkyl = Me,Et, i-Pr

The crystal structures of the organocobalt complexes, pyCo(GH)₂Me(1), pyCo(GH)₂Et(2) and pyCo(GH)₂Prⁱ(3) (py = pyridine, GH = monoanion of glyoxime) are reported. Compound (1) crystallizes in the space group P2₁2₁2₁ with cell parameters a = 8.508(1), b = 13.586(2) and c = 11.614(6) Å; (2) crystallizes in the space group P2₁2₁2₁ with cell parameters a = 8.448(4), b = 12.164(2) and c = 13.651(2) Å; (3) crystallizes in the space group P2₁/c with cell parameters a = 8.443(7), b = 12.913(2), c = 14.341(2) Å and β = 92.86(4).The three structures have been solved by Patterson and Fourier methods and refined by least squares methods to final R values of 0.045(1), 0.068(2) and 0.057(3) using 1819(1), 1653(2) and 1582(3) independent reflections. The pyCoalkyl fragment shows significant variation of CoN and CoC bond lengths. The latter increase from 2.003(4) to 2.084(9) Å following the increase of the alkyl bulk. The CoN(py) distances increase from 2.064(3) to 2.101(6) Å with the increasing σ-donor power of the alkyl group trans to pyridine. In comparison with cobaloximes having the same axial ligands, pyCo(DH)₂alkyl (DH = monoanion of dimethylglyoxime) does not show significant differences on the pyCo alkyl fragment. CoN axial bond lengths and exchange rates of the axial neutral ligand are consistent for the two series, although changes in bond lengths are detected only when rate constants are from two to three orders of magnitude different.     

Preparation and crystal structure of bis(acetato)(trans-1,2-diaminocyclohexane)platinum(II)

The structure of the complex [Pt(trans-1,2-di- aminocyclohexane) (acetate)₂]·H₂O has been determined by X-ray diffraction. This racemic compound is orthorhombic, space group Aba2, a = 20.813(9), b = 7.926(5), c = 17.296(8) Å, Z = 8. The structure was refined on 1214 nonzero Cu Kα reflections to R = 0.028. The square planar environment of Pt includes the amino groups of the diamine in cis positions and oxygens from two monodentate acetates. The PtN and PtO distances average 2.00(3) and 2.02(3) Å, respectively. The bite of the diamine ligand imposes a NPtN angle of 85(1)°, whereas the small OPtO angle of 85(1)° probably results from packing effects. The average plane through the puckered cyclohexyl ring makes an angle of 19° with the PtN₂O₂ plane. The molecules are stacked by pairs along the b axis. The two molecules of each pair are 180° apart about the stacking axis, and form altogether four NH···O hydrogen bonds.     

Metal—phenoxyalkanoic acid interactions. Part 14. The crystal and molecular structures of diaquabis(4-fluorophenoxyacetato)copper(II) bis(4-fluorophenoxyacetic acid)dihydrate and tetra-μ-(4-fluorophenoxyacetato-0,0′)-bis[(2-aminopyrimidine)copper(II)]

The crystal structures of two copper(II) complexes of 4-fluorophenoxyacetic acid (4-FPAH) have been determined by X-ray diffraction. [Cu(4-FPA)₂(H₂O)₂]·2(4-FPAH)·2H₂O (1) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 14.808(2), b = 9.832(2), c = 6.847(2) Å, α = 87.77(2), β = 98.41(2), γ = 112.33(2)° and was refined to a residual of 0.038 for 1697 ‘observed’ reflections. The coordination sphere in this complex is tetragonally distorted octahedral comprising two waters [CuO, 1.940(3) Å], two unidentate carboxylate oxygens [CuO, 1.942(2) Å] and two ether oxygens [CuO, 2.471(2) Å]. Two adducted [4-FPAH] acid molecules are linked to the un-coordinated oxygens of the acid ligands by hydrogen bonds [2.547(4) Å]. [Cu₂(4-FPA)₄(2-aminopyrimidine)₂] (2) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 12.688(2), b = 11.422(2), c = 7.951(1) Å, α = 78.74(1), β = 107.51(1), γ = 75.78(1)°, and was refined to a residual of 0.042 for 2683 ‘observed’ reflections. (2) is a centrosymmetric tetracarboxylate bridged dimer with four similar CuO (equatorial) distances [1.967–1.987 Å; 1.977(3) Å mean] and the axial position occupied by the hetero nitrogen of the 2-aminopyrimidine ligand [CuN, 2.176(3) Å]. The Cu---Cu separation is 2.710(1) Å. Crystal data are also presented which confirm the isostructurality of complex (2) with [Cu₂(phenoxyacetate)₄(2-aminopyrimidine)₂], the Co^II, Mg^II and Mn^II4-fluorophenoxyacetate complexes with their phenoxyacetic and 4-chlorophenoxyacetic acid analogues, and of Cd^II4-fluorophenoxyacetate with Cd^II and Zn^II phenoxyacetates.     

Characterization of a mononuclear copper carboxylate complex: Bis(acetylsalicylato)bis(pyridine)copper(II)

The preparation, spectral properties, and crystal structure of a mononuclear copper(II) complex of acetylsalicylate and pyridine are reported. The complex exists as bis(acetylsalicylato)bis(pyridine)copper(II) both in the solid state and in chloroform solution. The crystal is monoclinic, space group P2₁/n, with a = 17.823(5), b = 10.903(4), c = 6.598(2) Å, β = 95.74(2)°. The final refinement used 1472 observed reflections and gave an R of 0.046. The copper atom is surrounded by four atoms in a trans square planar arrangement with two short CuO distances of 1.949(3) Å and two CuN distances of 2.003(4) Å. Two longer CuO distances of 2.623(3) Å are made with the remaining oxygen atoms of the aspirin carboxylate groups.     

X-ray structure of a mono(1-methylthyminato) complex of cisplatin,chloro-(1-methylthyminato-N3)-cis-diammineplatinum(II) monohydrate

The crystal structure of chloro-(1-methyltyminato- N3)-cis-diammineplatinum(II) monohydrate, cis- (NH₃)₂Pt(C₆H₇N₂O₂)Cl·H₂O, is reported. The compound crystallizes in space group P$\text{1}$ with a = 6.911(2) Å, b = 8.598(3) Å, c = 11.464(4) Å, α = 100.13(3)°, β = 120.03(3)°, γ = 93.16(3)°, Z = 2. The structure was refined to R = 0.048 and R_w = 0.057. The compound contains the deprotonated 1-methylthymine ligand coordinated to Pt through N3 (1.973(10) Å). This distance represents the shortest Pt-N3(pyrimidine-2.4-dione) bond reported so far. The two PtNH₃ bond lengths differ significantly: PtNH₃ (trans to Cl) is longer (2.052(10) Å) than PtNH₃ (trans to N3 of 1-MeT) (2.002(11) Å). The PtCl distance (2.326(3) Å) is normal, as is the large dihedral angle between the Pt coordination plane and the nucleobase (76.5°).     

Synthesis and crystal and molecular structure of a methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate complex

Bis-Methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate, Dy[O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂]₂(NCS) was prepared from the combination of ethanolic solutions of Dy(NCS)₃·xH₂O and (CH₃O)₂P(O)CH₂C(O)N(C₂H₅)₂. The complex was characterized by infrared and NMR spectroscopy, and single crystal X-ray diffraction methods. The crystal structure was determined at 25 °C from 3727 independent reflections by using a standard automated diffractometer. The complex was found to crystallize in the monoclinic space group P2₁/c with a = 13.282(4) Å, b = 19.168(5) Å, c = 9.648(2) Å, β = 90.09(2)°, Z = 4, V = 2456.4 ų and ?_cald = 1.72 g cm^?3. The structure was solved by standard heavy atom techniques, and blocked least-squares refinement converged with R_f = 4.7% and R_wF = 4.9%. The Dy atom is seven coordinate and bonded in a bidentate fashion to two anionic phosphonate ligands [O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂^?] through the carbonyl oxygen atoms and one of two phosphonate oxygen atoms. In addition, each Dy atom is coordinated to two phosphonate oxygen atoms from two neighboring complexes and to the nitrogen atom of a thiocyanate ion. This coordination scheme gives rise to a two-dimensional polymeric structure. Some important bond distances include DyNCS 2.433(8) Å, DyO(carbonyl)_avg 2.39(2) Å, DyO(equat. phosphoryl)_avg 2.303(8) Å, DyO(axial phosphoryl)_avg 2.25(2), PO(phosphoryl)_avg 1.493(3) Å and CO(carbonyl)_avg 1.25(1) Å.     

The crystal and molecular structures of dioxo mo(VI) complexes of tripodal,tetradentate N,S-donor ligands

The crystal and molecular structures of the complexes MoO₂((SCH₂CH₂)₂NCH₂CH₂SCH₃), I and MoO₂((SCH₂CH₂)₂NCH₂CH₂N(CH₃)₂), II, have been determined from X-ray intensity data collected by counter methods. Compound I crystallizes in two forms, Ia and Ib. In form Ia the space group is P2₁/n with cell parameters a = 7.235(2), b = 7.717(2), c = 24.527(6) Å, β = 119.86(2)°, V = 1188(1) ų, Z = 4. In form Ib the space group is P2₁/c with cell parameters a = 14.945(5), b = 11.925(5), c = 14.878(4) Å, β = 114.51(2)°, V = 2413(3) ų, Z = 8. The molecules of I in Ia and Ib are very similar having an octahedral structure with cis oxo groups, trans thiolates (cis to both oxo groups) and N and thioether sulfur atoms trans to oxo groups. Average ditances are MoO = 1.70, MoS (thiolate) = 2.40, MoN = 2.40 and MoS (thioether) = 2.79 Å. Molecule II crystallizes in space group P2₁2₁2₁ with a = 7.188(1), b = 22.708(8), c = 7.746(2) Å, V = 1246(1) ų and Z = 4. The coordination about Mo is octahedral with cis oxo groups, trans thiolates and N atoms trans to oxo. Distances in the first coordination sphere are MoO = 1.705(2), 1.699(2), MoS = 2.420(1), 2.409(1) and MoN = 2.372(2), 2.510(2) Å. The conformational features of the complexes are discussed. Complex I displays MoO and MoS distances which are very similar to those found by EXAFS in sulfite oxidase. This similarity is discussed.     

Eight-coordination. Synthesis and structure of the schiff-base chelate bis(N,N′-disalicylidene-1,2-phenylenediamino)cerium(IV)

In an effort to elucidate the factors that determine the geometry of eight-coordinate complexes we synthesized and structurally characterizes the complex bis(N,N′-disalicylidene-1,2-phenylenediamino)Cerium(IV), Ce(salophen)₂. It is a square antiprismatic species with each chelating ligand spanning sss edges. The CeO bonds average 2.214 Å, appreciably shorter than CeN distance of 2.606 Å. The tow ligands have the sandwich orientation and the trapezoidal planes intersect at 88.2°. The δ angles are 7.0°, 2.6°, 56.5° and 55.9° and the ? angles are 30.0° and 28.6°. The complex crystallized in space group P2₁/C with Z = 4, a = 11.090(2) Å, b = 16.332(3) Å, c = 18.916(3) Å, β = 70.10(2)° and d_calc = 1.585 g/cm₃.     

Monomeric molybdenum(V) complexes. 4. The structure of tetraphenylarsonium oxodichloro(N-2-oxophenylsalicylideniminato)molybdate(V), [Ph4As] [MoOCl2(SalphO)]

The structure of [Ph₄As] [MoOCl₂(SalphO)], where SalphO is N-2-oxophenylsalicylideniminate dianion, has been determined by X-ray crystallography. The complex crystallizes in the monoclinic space group P2₁/n with a = 11.829(2), b = 16.149(3), c = 17.410(3) Å, β = 97.485(15)° and Z = 4. The calculated and observed densities and 1.566 and 1.573(10) g cm^?3, respectively. Block-diagonal least-squares refinement of the structure using 4722 independent reflections with I ? 3σ(I) converged at R = 0.0345 and R_w = 0.0484. The crystal contains [Ph₄As]⁺ cations and [MoOCl₂(SalphO)]^? anions. The Mo atom in the anion is in a distorted octahedral coordination environment. A planar terdentate Schiff base ligand occupies meridional positions with the N atom trans to the terminal oxo group (O_t). Two Cl atoms are cis to the O_t atom. The Mo atom is displaced by 0.33 Å from the equatorial plane toward the O_t atom. The MoO_t distance is 1.673(3) Å. The MoN bond trans to the O_t atom is 2.298(4) Å. The two MoCl bond lengths are 2.371(1) and 2.408(1) Å. The difference of 0.037 Å is significant (30 σ). Preparations of the title complex and the related complexes are also described.     

Synthesis and x-ray structure of a Hg(II) complex with adenine N(1)-oxide. A model for mercury binding to DNA

The synthesis and crystal structure of the adenine N(1)-oxide complex with mercury(II) chloride, (C₅H₅N₅O)HgCl₂ are reported. Crystals of the coordination compound belong to the monoclinic system, space group P2₁/n with the following primary crystallographic data: a = 6.685(1) Å, b = 11.798(2) Å, c = 10.155(1) Å, β = 100.22(1)°, V = 906.04 ų, Z = 4. The structure was elucidated by conventional Patterson and Fourier methods and refined by the full matrix least-squares technique on the basis of 1977 observed reflections to an R value of 0.074. The basic unit of the structure is a dimer, with a centre of symmetry, consisting of two HgCl₂ moieties and two adenine N(1)-oxide ligands. A polymeric structure results from the bridging interactions of chloride ions. Adenine N(1)-oxide acts as a bidentate bridging ligand, coordinating through N(7) and O(1). The coordination geometry around the mercury ion is a distorted square pyramid with N(7) and three chlorines (two of which are centro-symmetrically related) forming the square plane and O(1) occupying the axial position. Hg also interacts indirectly with N(6) through a Cl

HN hydrogen bond. Principal intracomplex geometrical parameters are as follows: HgN(7) = 2.61(1) Å, HgO(1) = 2.55(1) Å, HgCl(1) = 2.330(3) Å, HgCl(2) = 2.318(3) Å, HgCl(2′) = 3.347(3) Å. The cis angles range from 77.5° to 107.9° and the two trans angles are 155.5° and 163.1°. The centro-symmetrically related bases overlap partially and pack at a distance of 3.2 Å. The glide-related bases are linked by a hydrogen bond, N(9)H

O(1) and are inclined to one another by 109.7°. The results are compared with those derived from spectroscopic and other physicochemical studies on metal interaction with adenine N(1)-oxide. Based on the present structural observations and earlier experimental results a possible mechanism is proposed for mercury interaction with DNA.     

Preparation and structural characterization of di-μ-azido-bis[azido(2-aminopyridine)aquo]dicopper(II), [Cu(2-ampy)(N3)2(H2O)]2

Di-μ-azido-bis[azido(2-aminopyridine)aquo]dicopper(II), [Cu(2-ampy)(N₃)₂(H₂O)]₂, was synthesized and characterized by X-ray crystallography. The crystals are triclinic, space group P$\text{1}$, with a = 7.142(1), b = 7.812(1), c = 9.727(1) Å, a = 96.52(1), β = 95.52(1), γ = 113.47(1)°, and Z = 1. The structure was refined to R_F = 0.030 for 1960 observed MoKα diffractometer data. The dimeric molecule, which possesses a crystallographic inversion center, contains both terminal and μ(1)-bridging azido groups. Each copper(II) atom is further coordinated by a 2-aminopyridine ligand (via its ring N atom) and a water molecule to give a distorted square pyramid, with the metal atom raised by 0.17 Å above the N₄ basal plane [CuN (ring) = 2.001(2), CuN (azide) = 1.962(3)–2.018(2) Å] towards the apical aquo ligand [CuO = 2.371(2) Å]. Each water molecule forms an intramolecular O?HN (amine) acceptor hydrogen bond, and is linked by two OH?N (terminal azide) intermolecular donor hydrogen bonds to adjacent dimeric complexes to yield a layer structure parallel to (001). Infrared and electronic spectral data are presented and discussed.     

Crystal structure of [chloro(diethyldithiocarbamato)butyl phenyl]tin(IV)

The crystal structure of the title compound, SnCl(C₆H₅)(C₄H₉)[S₂CN(C₂H₅)₂], was determined and refined to an R factor of 3.2% for 4876 reflections. The molecule contains five-coordinate tin in a distorted trigonal bipyramidal arrangement with the tin atom lying 0.20 Å below the equatorial plane formed by one of the sulphur atoms, S(1), and the donor carbons of the butyl and phenyl groups. The chlorine and the other sulphur atom, S(2), occupy axial sites, making a S(2)SnCl angle of 156.85(1)°. The SnS(2) bond is markedly elongated (2.764(1) Å) compared to the SnCl bond (2.449(1) Å) and the SnS(1) bond (2.454(1) Å). The structure resembles those of analogues such as (C₆H₅)₂Sn(glygly) in having both hydrocarbon ligands located in the equatorial plane. Crystal data: space group P$\text{1}$: a = 8.291(2) Å, b = 14.726(3) Å, c = 9.509(2) Å, α = 96.24(2)°, β = 107.02(3)°, γ = 116.70(2)°, Z = 2, R = 3.2% for 4876 independent reflections.     

Metal-phenoxyalkanoic acid interactions. Part 15. The crystal structures of diaquabis(phenoxyacetato)cadmium(II) and catena-μ-[aquabis(phenoxyacetato-O)lead(II)-bis(phenoxyacetato)lead(II)]

The crystal structures of the cadmium(II) and lead(II) complexes of phenoxyacetic acid (PAH) have been determined by single crystal X-ray diffraction techniques. The cadmium complex, [Cd(PA)₂(H₂O)₂] (1), space group C2, with Z = 2 in a cell of dimensions, a = 11.801(2), b = 5.484(1), c = 13.431(3) Å, β = 100.87(2)°, possesses a distorted trapezoidal bipyramidal coordination around the metal atom, involving two water oxygens [2.210(5) Å] and four carboxyl oxygens from two symmetrical bidentate phenoxyacetate ligands [2.363(4), 2.365(4) Å] with Cd lying on the crystallographic two- fold axis. The lead complex, [Pb₂(PA)₄(H₂O)]_n(2) is triclinic, space group P$\text{1}$, Z = 2, with a cell of dimensions, a = 10.135(4), b = 10.675(3), c = 19.285(9) Å, α = 114.66(3), β = 91.94(3) and γ = 114.99(3)°. (2) is a two-dimensional polymer with a repeating dimer sub-unit. The first lead [Pb(1)] has an irregular MO₈ coordination [2.34?2.96(2) Å: mean, 2.63(2) Å] involving the water molecule, two oxygens from an asymmetric bidentate carboxylate group, two from a bidentate chelate [O(ether), O(carboxylate)] group and three from bridging oxygens, one of which also provides a polymer link to another symmetry generated lead. The second lead [Pb(2)] is irregular seven-coordinate [PbO, 2.48?2.73(2) Å: mean, 2.61(2) Å] with three bonds from the bridging groups, two from an unsymmetrical bidentate carboxylate (O, O′) group and one from a second carboxyl group which also bridges two Pb(2) centres in the polymer.     

The molecular structures of pyridine-chromiumpentacarbonyl and bis(pyridine)-chromiumtetracarbonyl

The structures of pyridinechromiumpentacarbonyl, (1), and bis(pyridine)chromiumtetracarbonyl,(2) have been determined. (1) crystallizes in the space group Pbam with a = 15.289(3) Å, b = 19.276(5) Å and c = 7.677(6) Å. (2) crystallizes in the space group P$\text{1}$ with a = 7.365(2) Å, b = 8.136(2) Å, c = 13.491(4) Å, α = 89.49(2)°, β = 88.89(2)°, and γ = 63.09(2)°. The structures refined to R_w values of 0.020 and 0.034 for (1) and (2), respectively. In both cases the pyridine rings are planar and stagger the cis CrCO bonds. A comparison of the structural results from these two compounds to piperidinechromiumpentacarbonyl and Cr(CO)₆ seems to indicate that the pyridine ligand is a weaker σ-donor and stronger π-acceptor than the saturated analog, piperidine.     

New preparations and molecular structures of cis-MCl2(Ph2PCH2PPh2)2, M = Ru,Os and trans-RuCl2(Ph2PCH2PPh2)2

The title compounds were made by reacting bis(diphenylphosphino)methane (dppm) with reduced solutions of OsCl₆^4? and Ru₂OCl₁₀^4?. The crystal and molecular structures of these compounds have been determined form three-dimensional X-ray study. The cis-isomers crystallize with one CHCl₃ per molecule of the complex. All three compounds crystallize in the monoclinic space group P2₁/n with unit cell dimensions as follows: Cis-OsCl₂(dppm)₂·CHCl₃: a = 13.415(4) Å, b = 22.859(4) Å, c = 16.693(3) Å, β = 105.77(3)°, V = 4926(3) ų, Z = 4. cis-RuCl₂(dppm)₂·CHCl₃: a = 13.442(3) Å, b = 22.833(7) Å, c = 16.750(4) Å, β = 105.53(2)°, V = 4953(3) ų, Z = 4. trans-RuCl₂(dppm)₂: a = 11.368(7) Å, b = 10.656(6) Å, c = 18.832(12) Å; β = 103.90(6)°, V = 2213(7) ų; Z = 2. The structures were refined to R = 0.044 (R_w = 0.055) for cis-OsCl₂(dppm)₂·CHCl₃; R = 0.065 (R_w = 0.079) for cis-RuCl₂(dppm)₂·CHCl₃ and R = 0.028 (R_w = 0.038) for trans-RuCl₂(dppm)₂. The complexes are six coordinate with stable four-membered chelate rings. The PMP angle in the chelate rings is ca. 71° in each case.     

Localization of repetitive and unique DNA sequences neighbouring the rabbit beta-globin gene

The structure of oxymyoglobin has been refined at 1·6 Å resolution, using diffractometer data collected at ?12 °C. The crystallographic R factor is 0·159, and the atomic positions are known to 0·1 Å accuracy in internal segments of the molecule.The iron atom lies 0·22(3) Å from the plane of the porphyrin, 0·25 Å closer than in deoxymyoglobin, and the F helix has moved by a similar amount. Oxygen binds to the iron in a bent, end-on arrangement, with FeOO = 115(5) ° and FeO = 1·83(6) Å. The mean FeN(porphyrin) bond length is 1·95(6) Å, 0·08 Å shorter than in deoxymyoglobin, but the difference is not significant compared to the experimental error. FeN_ε(His8F) is 2·07(6) Å, the same as in model compounds. Movements of the haem, iron, F helix and FG corner on oxygenation are similar to those found in the T-R state transition in haemoglobin, but are smaller in magnitude.     

Nickel—nitrosyl Complexes: structure of nitrosyltris(trimethylphosphine)nickel hexafluorophosphate, {Ni(NO)(PMe3)3} PF6

The crystal and molecular structure of nitrosyltris-(trimethylphosphine)nickel(O) hexafluorophosphate, {Ni(NO)(PMe₃)₃}PF₆, has been determined from three dimensional single crystal X-ray analysis. The compound crystallizes in the orthorhombic space group Pnma with Z = 4 and a unit cell of dimensions: a = 16.253(3), b = 10.536(1) and c = 12.228(2) Å. The structure was solved by conventional heavy atom techniques and refined by least-squares methods to R₁ = 0.036 and R₂ = 0.048 respectively for 1085. independent reflections. The coordination geometry around the nickel is a slightly distorted tetrahedron with an average PNiP angle of 105.63° and PNiN angle 113.03°. The nickel nitrosyl group is slightly bent with an NiNO angle of 175.4(5)°. The bending occurs in the ClPlNiNO plane toward Pl. The structure is compared with other tetrahedral {MNO}¹⁰ phosphine complexes and the MNO bonding is discussed.