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.     

Decay of individual Escherichia coli trp messenger RNA molecules is sequentially ordered.

Human fluoromethaemoglobin with inositol hexaphosphate (IHP) in 0.05 m-phosphate buffer was crystallized by addition of polyethylene glycol (PEG). The crystals are isomorphous with those of deoxyhaemoglobin A without IHP grown in solutions containing PEG by Ward et al. (1975). The structure was investigated by means of a difference Fourier synthesis against deoxyhaemoglobin A based on X-ray data collected within a limiting sphere of 3.5 Å^?1. The four subunits are arranged in the quaternary T structure and IHP is bound at the same site between the β chains as in deoxyhaemoglobin. In both the α and β haem regions the distance between the haem plane and the F helix is reduced in fluoromethaemoglobin relative to deoxyhaemoglobin and the iron atom is moved from the proximal towards the distal side of the plane, but the change, if any, in the distance between the iron and the N_ε of the proximal histidine cannot be clearly established. The α Fe in fluoromethaemoglobin is either in the haem plane or up to 0.8 Å on the distal side, suggesting the possibility of rupture of the bond to the histidines N_ε; it was not possible to estimate the position of the β iron. The main spectral changes associated with the reaction of fluoromethaemoglobin with IHP take place in less than 3 ms at room temperature.     

Quaternary structures and low frequency molecular vibrations of haems of deoxy and oxyhaemoglobin studied by resonance Raman scattering

The influence of quaternary structure on the low frequency molecular vibrations of the haem within deoxyhaemoglobin (deoxy Hb) and Oxyhaemoglobin (oxy Hb) was studied by resonance Raman scattering. The FeO₂ stretching frequency was essentially identical between the high affinity (R) state (Hb A) and low affinity (T) state (Hb Kansas and Hb M Milwaukee with inositol hexaphosphate). However in deoxy Hb, only one of the polarized lines showed an appreciable frequency shift upon switch of quaternary structure, i.e. 215 to 218 cm^?1 for the T state (Hb A, des-His(146β) Hb, and des-Arg(141α) Hb (pH 6.5)) and 220 to 221 cm^?1 for the R state (des-Arg(141α) Hb (pH 9.0), des-His(146β)-Arg(141α) Hb and NES des-Arg(141α) Hb). Based on the observed ⁵⁴Fe isotopic frequency shift of the corresponding Raman lines of deoxy Hb A (214 → 217 cm^?1), of deoxy NES des-Arg Hb (220 → 223 cm^?1), of the protoporphyrinato-Fe(II)-(2-methylimidazole) complex in the ferrous high spin state (207 → 211 cm^?1) and of deoxymyoglobin (220 → 222 cm^?1) (Kitagawa et al., 1979), and on substitution of perdeuterated for protonated 2-methylimidazole in the deoxygenated picket fence complex (T_pivPP)Fe²⁺ (2-MeIm) (209 → 206 cm^?1), and on the results of normal co-ordinates calculation carried out previously, we proposed that the 216 cm^?1 line of deoxy Hb is associated primarily with the FeN_ε(HisF8) stretching mode and accordingly that the FeN_ε(HisF8) bond is stretched in the T state due to a strain exerted by globin.     

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.     

Short hydrogen bond: Spectral studies and X-ray structure of bis(alpha-picoline N-oxide)-hydronium tetrachloroaurate(III)

Spectral and the X-ray diffraction studies of the title compound [H(2-picNO)₂] [AuCl₄] (2-picNO = alpha-picoline N-oxide) were done to investigate the short hydrogen bond in the dimeric cation [H(2-picNO)₂]⁺. The compound exhibits several narrow transmission bands overlaid on a broad continuous absorption characteristic of a short hydrogen bond; it crystallizes with four molecules in a monoclinic unit cell of space group P2₁/n with lattice parameters a = 22.376(9), b = 9.874(6), c = 7.957(5) Å and β = 94.98(6)°. The structure was solved using 2623 data points collected on a CAD4 to the final value for R(F_o) = 0.039. The structure consists of discrete [AuCl₄]^? and [H(2-picNO)₂]⁺ ions. Contrary to all known examples, the dimeric cation in this compound has a short hydrogen bond having no symmetry constraints making the present structural analysis unique in this series of compounds. The O—O distance is 2.393(6) Å and the dihedral angle between the two planar 2-picNO moieties in the cation is 44.1°. The [AuCl₄]^? anion is planar with an average AuCl distance of 2.268(2) Å. The infrared spectrum and the structure of the compound is compared with the related structures.     

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 spectroscopic properties of CpRuCl(R-DAB(4e)) and CpRuCo(CO)3(R-DAB(6e)). Part XVII. X-ray structure determination of CpRuCo(CO)3(t-Bu-DAB(6e))

CpRuCl(PPh₃)₂ reacted with excess R-DAB in refluxing toluene to give CpRuCl(R-DAB(4e)) (1a: R = i-Pr; 1b: R = t-Bu; 1c: R = neo-Pent; 1d: R =p-Tol). ¹H NMR and ¹³C NMR spectroscopic data indicated that in these complexes the R-DAB ligand is bonded in a chelating 4e coordination mode.Reaction of 1a and 1b with one equivalent of [Co(CO)₄]⁻ afforded CpRuCo(CO)₃(R-DAB(6e)) (2a: R = i-Pr; 2b: R = t-Bu). The structure of 2b was determined by a single crystal X-ray structure determination. Crystals of 2b are monoclinic, space group P2₁/n, with four molecules in a unit cell of dimensions: a = 16.812(4), b = 12.233(3), c = 9.938(3) Å and β = 105.47(3)°. The structure was solved via the heavy atom method and refined to R = 0.060 and R_w = 0.065 for the 3706 observed reflections. The molecule contains a RuCo bond of 2.660(3) Å and a cyclopentadienyl group that is η⁵-coordinated to ruthenium [RuC(cyclopentadienyl) = 2.208(3) Å (mean)]. Two carbonyls are terminally coordinated to cobalt (CoC(1) = 1.746(7) and CoC(2) = 1.715(6) Å) while the third is slightly asymmetrically bridging the RuCo bond (RuC(3) = 2.025(6) and CoC(3) = 1.912(6) Å). The RuC(3)O(3) and CoC(3)O(3) angles are 138.4(5)° and 136.5(5)°, respectively. The t-Bu-DAB ligand is in the bridging 6e coordination mode: σ-N coordinated to Ru (RuN(2) = 2.125(4) Å), μ₂-N′ bridging the RuCo bond and η²-CN coordinated to Co (RuN(1) = 2.113(5), CoN(1) = 1.941(4) and CoC(4) = 2.084(5) Å). The η²-CN′ bonded imine group has a bond length of 1.394(7) Å indicating substantial π-backbonding from Co into the anti-bonding orbital of this CN bond.¹H NMR spectroscopy indicated that 2a and 2b are fluxional on the NMR time scale. The fluxionality of 6e bonded R-DAB ligands is rarely observed and may be explained by the reversible interchange of the σ-N and η²-CN′ coordinated imine parts of the R-DAB ligand.     

On the structure of Hg2I3+ in dimethylsulfoxide and aqueous solution. An X-ray scattering and raman spectroscopic study

Dimethylsulfoxide and aqueous solutions of mercury(II) in large excess over iodide have been investigated by X-ray scattering techniques supported by Raman spectroscopic measurements. The composition of the solutions has been selected to ensure that the cationic complex Hg₂I³⁺ is the predominant iodide species. The structure parameters of the solvated Hg₂I³⁺ ion have been refined by a least- squares procedure on the scattering data, using known structural parameters for the additional molecular entities present. The Hg₂I³⁺ entity is more or less identical in DMSO and water. The HgI bond distance is 2.613(12) and 2.632(5) Å and the HgHg distance is 3.66(5) and 3.70(1) Å in DMSO and water, respectively. This yields a HgIHg angle of 89° in both solvents. The mercury(II) atom in this complex is most probably solvated in a tetrahedral fashion by three DMSO or H₂O molecules. The structure of Hg₂I³⁺ is discussed in the light of recent results for the Ag₄I³⁺ complex in solution and relevant crystal structures.     

Refinement of human lysozyme at 1.5 Å resolution analysis of non-bonded and hydrogen-bond interactions

The structure of human lysozyme has been crystallographically refined at 1.5 Å resolution by difference map and restrained least-squares procedures to an R factor of 0.187. A comprehensive analysis of the non-bonded and hydrogen-bonded contacts in the lysozyme molecule, which were not restrained, revealed by the refinement has been carried out. The non-bonded CC contacts begin at ~3.45 Å, and the shorter contacts are dominated, as expected, by interactions between trigonal and tetrahedral carbon atoms. The CO contact distances have a “foot” at 3.05 Å. The CN distance plot shows a significant peak at 3.25 Å, which results from close contact between peptide NHs and carbonyl carbons involved in N_iC′_{i ? 2} interactions in α-helices and reverse turns. The distances involving sulphur atoms discriminate SC trigonal interactions at 3.4 to 3.6 Å from SC tetrahedral interactions at 3.7 Å. All these types of non-bonded interactions show minimum distances close to standard van der Waals' separations.Analysis of hydrogen-bond distances has been carried out by using standard geometry to place hydrogen atoms and measuring the XHO distances. On this basis, there are 130 intramolecular hydrogens: 111 NHO bonds, of which 69 are between main-chain atoms, 13 between side-chain atoms and 29 between mainchain and side-chain atoms. If a cluster of four well-defined internal water molecules is included in the protein structure, there is a total of 19 OHO hydrogen bonds. The mean NO, NHO distances and HN?O angles are 2.96 ± 0.17 Å, 2.05 ± 0.18 Å and 18.5 ± 9.6 °, and the mean OO, OHO distances and HÔO angles are 2.83 ± 0.19 Å, 1.98 ± 0.26 Å and 23.8 ± 13.4 °. The distances agree well with standard values, although the hydrogen bonds are consistently more non-linear than in equivalent small molecules. An analysis of the hydrogen-bond angles at the receptor atom indicates that the α-helix, β-sheet and reverse turn have characteristic angular values. A detailed analysis of the regularity of the α-helices and reverse turns shows small but consistent differences between the α-helices in lysozyme and the current standard model, which may now need revision. Of the 21 reverse turns that include a hydrogen bond, the conformations of 19 agree very closely with four of the five standard types. We conclude that the restrained least-squares method of refinement has been validated by these analyses.     

Preparation,properties and crystal structures of nickel(II) complexes with acyclic schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane or 3,3′-diamino-N-methyl-dipropylamine

Nickel(II) complexes with the compartmental Schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane (H₂L¹) or 3,3′-diamino-N-methyl-dipropylamine (H₂L²) were synthesized, and the crystal structures of [Ni(L¹)- (py)₂] and [Ni(L²)(dmf)]·H₂0 were determined by X-ray crystallography.Ni(L¹)(py)₂ is monoclinic, space group C2/c, with a= 18.457(6), b = 11.116(7), c= 16.098(6) Å, and β = 115.79(5)°; D_c = 1.49 g cm⁻³ for Z = 4. The structure was refined to the final R of 6.9%. The molecule has C₂ symmetry. The nickel atom is six-coordinated octahedral. Selected bond lengths are: NiO 2.04(1) Å, NiN (L¹) 2.08(1) Å, NiN(py) 2.17(1) Å.[Ni(L²)(dmf)]·H₂O is monoclinic, space group P2₁/n, with a = 17.329(6), b = 13.322(7), c = 12.476(7) Å and β = 95.43(5)°; D_c = 1.45 g cm⁻³ for Z = 4. The structure was refined to the final R of 5.1%. The nickel atom is bonded in the octahedral geometry to the bianionic pentadentate ligand L² and to one molecule of dimethylformamide. Selected bond lengths are: NiO (charged) 2.063(3) Å (mean value), NiO (neutral) 2.120(3) Å, NiN (planar) 2.050(3) Å (mean value), NiN (tetrahedral) 2.177(3) Å.     

Mechanistic Studies on Metal-pyrophosphate Hydrolysis. Structure of Tetraammine(chloroaquo)cobait(III) dichloride ([CO(NH3)4ClH20]2+•-2Cl−), an Acid Hydrolysis Product of Co(NH3)4HP2O7 and Co(NH3)4PO4

Abstract

The octahedral complex tetraammine(chloroaquo)cobalt(III) dichloride is shown to be the HCl hydrolysis product of both P¹,^2-bidentate tetraammine(pyrophosphato)cobalt(III) [CO(NH₃)₄HP₂0₇ or CoPP] and bidentate tetraammine(phosphato)cobalt(III) [Co(NH₃)₄P0₄or CoP]. The complex crystallizes in the orthorhombic space group Pna2¹ with cell dimensions α=13.033(2)Å, b=6.710(1) Å, and c=10.318(2)Å; the crystal structure was refined to a final disagreement index of 0.033. The average of the four Co-N distances is 1.944±6Å. The Co-Cl distance is 2.257(2)Å and the Co-O(W) distance is 1.971(4)Å. Both protons of the coordinated water molecule are engaged in strong hydrogen bonds to the two nonbonded chloride counterions with 0(W)-C1 distances of 3.087(6)Å and 3.123(6)Å. Each nonbonded chloride is engaged in seven hydrogen bonding interactions resulting from the high ratio of hydrogen bond donors to acceptors in the CoP structure. Cobalt bisphosphate (CoP₂) is the final enzyme hydrolysis product when CoPP is used as substrate in the yeast inorganic pyrophosphatase reaction. The bridge oxygen atom is the site of initial CoPP cleavage both, for HCl catalyzed hydrolysis as well as for enzyme catalyzed hydrolysis.     

Synthesis,structural characterization,and properties of the organothorium alkylthiolate complex [(CH3)5C5]2Th(SCH2CH2CH3)2

This contribution reports the synthesis and characterization of the organothorium alkylthiolate complex [(CH₃)₅C₅]₂Th(SCH₂CH₂CH₃)₂. This compound crystallizes in the monoclinic space group C2/c (#15) with four molecules in a cell of dimensions a=19.066(2), b=11.603(1), c=16.379(2) Å, and β=130.08(1)°. Least-squares refinement led to a value for the conventional R index (on F_o) of 0.040 for 132 variables and 2030 observations having F_o²⩾3σ(F_o²). The molecular structure consists of an unexceptional ‘bent sandwich’ [(CH₃)₅C₅]₂Th fragment coordinated to two n-propylthiolate ligands. The ThS bond distance is 2.718(3) Å; the SC(α) distance, 1.78(2) Å; the ThSC(α) angle, 108.3(5)°; and the SThS′ angle, 102.5(2)°. Contrasts are drawn with the structures of analogous actinide alkoxides     

X-ray structure of dimeric [Co(poph)(NCS)2]2, an N-oxide-bridged cobalt(II) complex with 2-pyridinecarboxaldehyde 1-oxide 2′-pyridinylhydrazone (poph)

An X-ray structure determination is reported for the N-oxide-bridged dimeric complex [Co(poph)- (NCS)₂]₂ with 2-pyridinecarboxaldehyde 1-oxide 2′-pyridinylhydrazone (poph). The complex is monoclinic, P2₁/c, with a = 12.460(7), b = 9.884(3), c = 16.562(8) Å, β= 127.60(2)° and Z = 4. The ligand coordinates as a planar ONN tridentate via the N-oxide oxygen and the hydrazone and pyridyl nitrogens. A second out-of-ligand-plane bond from the N-oxide oxygen to another cobalt produces a centrosymmetric N-oxide-bridged structure. The in-ligand and out-of-ligand-plane CoO distances are 2.028(5) and 2.460(5) Å, respectively. Each cobalt(II) is octahedrally coordinated by two cisN- bonded thiocyanates, by an ONN-bonded poph molecule, and by a bridging N-oxide oxygen. This is the first structure report of a pyridine N-oxide. bridged cobalt(II) complex.     

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.     

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.     

Resonance Raman scattering on the haem group of cytochrome c

Resonance Raman spectra of the haem group of 8 × 10^?5 M horse heart ferro- and ferricytochrome c solutions have been obtained. The spectra are almost identical to that of haemoglobin. The frequency of the Raman line near 1370 cm^?1, which in haemoglobin is sensitive to the position of the haem iron, indicates that the iron atom of cytochrome c lies in the plane of the porphyrin for both oxidation states.     

Synthesis and structure of μ-3,3′-[ 1,2-ethanediyl-bis(nitrilomethylidyne)-bis(2-hydroxybenzoato)] aquadicopper(II) hydrate

The complex μ-3,3′-[1,2-ethanediyl-bis(nitrilome- thylidyne)-bis(2-hydroxybenzoato)] aquadicopper(II) hydrate, C₁₈H₁₆N₂O₈Cu₂, was isolated from an attempted preparation of a copper lanthanum binuclear complex. The dark purple crystals are monoclinic, space group P2₁/n, with 4 molecules per unit cell; dimensions a = 13.961(5), b = tl.787(3), c = 11.622(3) Å and β = 113.09(2)°. The final R was 0.046 for the 2062 reflections used in the analysis. The Cu atom in the N₂O₂ cavity is five coordinate with CuN distances of 1.879 and 1.880 Å and CuO distances of 1.898 and 1.900 Å. A water molecule at 2.557 Å completes the square pyramidal arrangement. The second Cu in the O₄ cavity is square planar, with CuO distances to the bridging oxygens of 1.914 and 1.909 Å and to the carboxy oxygens of 1.871 and 1.882 Å. A survey of copper complexes in a square planar N₂O₂ arrangement has led to the equation δCu from the N₂O₂ plane = 0.822 – 0.275 (CuO axial distance) with a correlation coefficient of 0.98 for the 12 structures in which the Cu atom is bonded to a fifth oxygen atom. A model for the transition from square planar to square pyramidal geometry is proposed.     

The crystal and molecular structure of bis(2,2′-dipyridylamine-N,N′)di(nitrato-O)cadmium(II); Solid state 113Cd NMR,components and orientation of the chemical shift tensor relative to the donor ligands

The structure of the titled compound has been determined and refined. The structure consists of isolated molecules separated by ordinary Van der Waals' distances. The Cd atom is on a crystallographic center of symmetry. The coordination polyhedron of the Cd atom is distorted octahedral with four pyridine nitrogen donors in the equatorial plane and with axial oxygen atoms from the nitrate groups. The CdO distance is 2.599(4) Å, the CdN distances are 2.310(4) and 2.316(3) Å, and the NCdN bite angle is 79.0(1)°. The solid state magic angle spinning/cross polarization ¹¹³Cd NMR isotropic chemical shift is +51.4 ppm and the components of the chemical shift tensor are: S₁₁= −92 ppm, S₃₃ = +208 ppm and S₂₂ = +39 ppm and their directions are: in the CdN₄ plane and bisecting the NCdN bite angle, perpendicular to the CdN₄ plane and the third perpendicular to the other two, respectively. This permits the assignment of contributions to the chemical shift tensor of 50 ppm from pyridine nitrogen and of −50 ppm from nitrate oxygen. From the tensor components, atomic nitrogen can be distinguished from aliphatic nitrogen donors. Crystal data: C₂₀H₁₈O₆N₈Cd; M_r = 578.8, F(000) = 580, monoclinic, P2₁/c, a = 8.591(1), b = 16.496(2), c = 7.878(1) Å, β = 95.97°, λ = 0.71073 Å, Mo Kα, V = 1110(1) ų. Z = 2, D_m = 1.73(2), D_x = 1.73 g/cm³, μ = 10.3 cm⁻¹, R_f = 0.039, 1834 reflections, 160 parameters, T ∼ 298 K. Refinement was by full matrix least-squares with anisotropic temperature factors.     

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.     

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.