Takehiro Ozawa

Molecular and crystal structures of trans-[VOCl2(H2O)2] hydrogen bonded adducts with 15-crown-5 and benzo-15-crown-5 ether

Abstract The crystal structures of molecular adducts of vanadyl complex of trans-[VOCl2(H2O)2] with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) have been studied by X-ray diffraction at ambient temperature. The adduct of the same complex with 18-crown-6 (18C6) recrystallized from a solvent different from that previously reported, has been also re-refined and the unresolved chloro position has been resolved into two disordered positions. The ClVCl bond angles in the 15C5 and B15C5 adduct are 143° and 145°, respectively, which are smaller than the OVO bond angles of 153° and 154°. There appear eclipsed type H2O-VCl2 conformations in all the adducts. These observations can be ascribed to the steric repulsion between the chloro ligands and aqua hydrogen atoms as well as to the coulombic repulsion between the chloro and oxido ligand. The crystals are composed of adduct polymers with 1 : 1 stoichiometry in which the chromophore and crown ether alternate along the polymer axis. The polymers are formed by hydrogen bonding between the aqua ligand and the oxygen atoms on the crown ring. The crown ethers adopt invariably all-gauche CC conformation. The OC bonds are of trans conformation except for a gauche OC bond in 15C5. ESR parameters of trans-[VOCl2(H2O)2] observed for the 15C5 adduct powder are also presented.

Nephelauxetic series of in-plane ligands for square-pyramidal nitridochromium(V) complexes as studied by means of ESR spectroscopy

Abstract The crystal structure of the nitridochromium(V) complex [CrN(salophen)]·MeCN [H2salophen=N,N′-bis(salicylidene)-o-phenylenediamine] has been determined. The coordination geometry of this complex, similar to those of all the nitridochromium(V) complexes investigated so far, is square pyramidal with the nitride ion occupying the apex. The ESR parameters of the nitridochromium(V) complexes isolated so far were compared with one another to show an enormous expansion of the 3d electron cloud due to the strong CrN triple bonding. Moderate covalency in the in-plane bonds was also concluded. The nephelauxetic series of three types of the basal ligands is deduced to be salen≈salophen>bpb≈mebpb≈dmebpb>oep≈ttp (in nephlauxetic ratio) for the high-oxidation nitridochromium(V), H2salen=N,N′-bis(salicylidene)ethane-1,2-diamine, H2bpb=1,2-bis(pyridine-2-carboxamido)benzene, H2mebpb=1,2-bis(pyridine-2-carboxamido)-4-methylbenzene, H2dmbpb=1,2-bis(pyridine-2-carboxamido-4,5-dimethylbenzene, H2oep=2,3,7,8,12,13,17,18-octaethylporphyrin and H2ttp=5,10,15,20-tetra-p-tolylporphyrin.

A crystal modification of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene: X-ray molecular structure and proton tautomerism of the highly π-conjugated form

The crystal structure for one of crystal modifications of the title compound (taa) has been determined by X-ray diffraction at room temperature. The crystal system is monoclinic with a space group of P21/a : a=14.926(2), b= 5.2342(8), c=19.570(2)A, β=112.195(7)°, Z= 4. The final R factor is 0.033 for 1 443 observed reflections to 270 variables. The crystals recrystallized from xylene have been proven to be a different crystal modification from those obtained by vacuum sublimation at 250 °C. In the present crystal, two independent molecules are located on the crystallographic centres of symmetry. Each of them shows positional disorder at the amino hydrogen atoms. This modification does not exhibit the alternation of the bond lengths in the 1,3-propanediiminato linkage beyond the limit of ΔI < 3σ(I), which is the case for a previously reported crystal modification. These findings lend support to dynamic imine-enamine tautomerization rather than static disorder. The difference Fourier map suggests a double-minimum potential for the proton tautomer ism. Rapid tautomerization in [2H8]toluene solution can be observed by 1H NMR spectroscopy down to –90 °C, just above the melting point of the solvent.

Crystal structure of conglomerates of trans(O)-N(2-aminoethyl)-N-(carboxymethyl) glycinatoaquachlorocobalt(III) and of mer(N)-N,N,-bis(2-aminoethyl) glycinatoaquachlorocobalt(III) perchlorate

Abstract The title complexes trans (O)-(Co(aeida)Cl(H 2 O)] ( A ) and mer (N)-[CoCl (i-dtma)(H 2 O)] ClO 4 ( B ) crystallize as a conglomerate (H 2 aeida = N-(2-aminoethyl)-N-(carboxymethyl)glycine, Hi-dtma = N,N-bis(2-aminoethyl)glycine). The X-ray crystallographic analysis shows that single crystals of A and B are chiral. Although the conglomerate formation of either A and B was not observed in the crystal morphology under a microscope, it was confirmed by the Weissenberg photography method. In A , the chirality originates from the δ or λ conformation of the ethylenediamine chelate ring. In B it originates from the fact that chiralities due to the δ and λ conformation of the two ethylenediamine chelate rings in the complex do not cancel out, owing to the asymmetry derived from the rotational configuration of the aqua ligand. These chiral molecular configurations are closely related with intermolecular hydrogen bonds in the crystal.

Crystal structure of hexafluoro-2,4-pentanedionato complexes of cobalt(III). [(Co(hfac)(en)2][ClO4)2 and β-[Co(hfac)(trien)](ClO4)2

Abstract The crystal structures of [Co(hfac)(en) 2 ](ClO 4 ) 2 ( I ) and β-[Co(hfac) (trien)](ClO 4 ) 2 ( II ) have been determined by X-ray diffraction at ambient temperature, where Hfac = hexafluoro-2,4-pentanedione, en = ethylenediamine and trien = 1,8-diamino-3,6-diazaoctane. The relative configuration of the cation in II is rel -Δ- RR . Their molecular structures are compared with those previously reported for [Co(hfacOH)(en) 2 ] + , [Co(hfacOH 3 )(en) 2 ] + and β-[Co(hfacOCH 3 )(trien)] + , in which an OH − or OCH 3 − anion is covalently combined with one of the carbonyl carbon atoms on the hfac ligand. The quasiaromaticity of the coordinating hfac ligand in I and II was structurally characterized.

CRYSTAL AND MOLECULAR STRUCTURES OF MER (N)-DINITRO-N,N-BIS(3-AMINOPROPYL)GLYCINATO COBALT(III) AND OF BROMIDE, PERCHLORATE AND NITRATE SALTS OF MER ( N)-AQUACHLORO-N,N-BIS(3-AMINOPROPYL)GLYCINATO COBALT(III)

Abstract X-ray structural analyses have been made on single crystals of mer(N)-[Co(5-dptma)(NO2)2] (A), mer(N)-[CoCl(5-dptma)(H2O)] Br (B), mer(N)-[CoCl(5-dptma)(H2O)]ClO4 (C) and mer(N)-[CoCl(5-dptma)(H2O)] NO3 (D), where H(5-dptma) is N,N-bis(3-aminopropyl)glycine. Complex A crystallizes in the monoclinic space group P21/c as a racemate; complex B in the monoclinic space group P21/n as a racemate; complex C in the orthorhombic space group P212121 as a conglomerate; and complex D in the orthorhombic space group Pna21 as a racemate. In these complexes, the tripod quadridentate 5-dptma coordinates to cobalt(III) with its three nitrogen atoms on a meridian of the coordination octahedron and with the six-membered chelate rings assuming the chair conformation. In A the molecular planes of the NO2− ligands are anchored by intramolecular and intermolecular hydrogen bonds to the amine protons. The molecular planes of the aqua ligands in B, C and D are anchored by two intermolecular hydrogen bonds; one with the carbonyl oxygen atom and the other with the counter anion.

Molecular and crystal structure of 9-[α-(9H-fluoren-9-ylidene)-4-chlorobenzyl]-9H-fluoren-9-yl; an organic antiferromagnet with TN= 3.25 K

The crystal structure of the title radical has been determined by X-ray diffraction at ambient temperature. The crystal system is monoclinic with a space group of Cc: a= 33.204(4), b= 9.391(1), c= 15.290(1)A, β= 101.223(7)°, Z= 8. The final R factor is 0.035 for 2623 observed reflections. There are two crystallographically independent molecules constituting a pair of atropisomers. Two fluoren-9-yl groups and a chlorophenyl moiety are arranged in a propeller shape. The range of the torsion angles of the fluorenyl blades is 25°∼ 33°, and that of the chlorophenyl blades is 55°∼ 59°. The electron-spin exchange pathways are discussed based on the McConnells spin-density Hamiltonian. The exchange-coupled neighbours are estimated to be z= 6, to which the highest TN among organic radicals can be attributed.

Spectroscopic studies of the trans-[VOCl2(H2O)2] chromophore in its hydrogen bonding adduct with 18-crown-6

Abstract An electron paramagnetic resonance (EPR) study has been carried out on a single crystal of trans-[VOCl2(H2O)2](18- crown-6)·2H2O or adduct of trans-diaquadichlorooxovanadium(IV) with 1,4,7,10,13,16-hexaoxacyclooctadecane (abbr. 18C6) at ambient temperature. This crystal belongs to a centric triclinic space group, and the chromophore and crown ether alternate to form a magnetically diluted vanadyl system. The EPR study has revealed the rhombic spin Hamiltonian parameters gz = 1.952(1), gx = 1.985(2), gy = 1.990(3), ∣Az∣ = 18.8(3), ∣Ax∣ = 7.6(3) and ∣Ay∣ > 5.5 mT, where the z, x and y principal axes are along the VO and nearly along the VOH2 and VCl bonds, respectively. Errors of these parameters are large, especially in Ay, owing to many broad hyperfine linewidths resulting in overlapping. A negative sign is suggested for all the principal A values. Three d-d* transitions, dxy→dyz (12.9 kcm−1), dxy→dyz (15.2) and dxy→dx2−y2 (17.0), and a charge-transfer transition, a1(related to dx2−y2)→a2(dxy) (27–28 kcm−1) from the acetone solution, were assigned. The trans-[VOCl2(H2O)2] species is not dissociated in acetone and 2-propanol solution, but the chloro ligands are substituted with aqua ligands when there is a lot of water in the solution.

Spectroscopic studies of a square-pyramidal nitridochromium(V) complex

The ESR and UV/VIS spectra have been studied for solutions of [N,N′-bis(pyridine-2-carbonyl)-o-phenylenediamido]nitridochromium(V) having a square-pyramidal (CrN5) chromophore. The g and 53Cr hyperfine coupling tensors (A) are axially symmetric. An analysis of the A tensor indicated a 3dxy ground-state Kramers doublet. Fairly high dπ–pπ interaction in the CrN formally triple bond was also revealed. The striking stability of this complex can be attributed to the remarkable dπ–pπ covalency of the CrN bond. None of the d–d* transitions has been observed in the region of λ 600 nm at room temperature. Bands at 25 000 and 29 000 cm–1 have been tentatively assigned to charge-transfer transitions. The considerable difference between the A⊥(53Cr), a(53Cr), g⊥ and giso values of nitrido-and those of oxo-chromium(V) complexes have been explained in terms of the different extents of covalency in the CrN and CrO multiple bonds.