Leslie F. Larkworthy

NEW TETRADENTATE SCHIFF BASES, THEIR OXOVANADIUM(IV) COMPLEXES, AND SOME COMPLEXES OF BIDENTATE SCHIFF BASES WITH VANADIUM(III)

Abstract New vanadyl(IV) complexes of tetradentate Schiff-base dianions containing one, two or three carbon atoms between the two iminato-nitrogen atoms are described. The compounds are either mononuclear or polymeric, as shown by the value of v(V=O), and depending upon the Schiff-base dianion. There is no evidence for electron delocalization along the polymeric chains. Some vanadium(III) complexes of bidentate Schiff-base monoanions have also been isolated; the crystal structure of [VO(2-OC6H4CHNH)2] and preliminary data on the structure of [V(Prhap)3]·toluene [HPrhap = 2-HOC6H4C(Me)NCH2CH2Me] are reported.

Facile synthesis of complexes of vanadium(II) and the crystal and molecular structures of hexaaquavanadium(II) trifluoromethylsulphonate

Abstract The new vanadium(II) salt [V(H2O)6](CF3SO3)2 was crystallised from solutions obtained by dissolving metallic vanadium in aqueous trifluoromethylsulphonic acid. The cations in this complex are regular octahedra (VO distance=2.119(1) A) and are extensively hydrogen-bonded to the anions throughout the lattice. The salt is soluble in several organic solvents and should be a useful starting material in the preparation of vanadium(II) complexes. Thus [V(ethylenediamine)3](CF3SO3)2 has been prepared by the addition of ethylenediamine to a solution of [V(H2O)6](CF3SO3)2 in ethanol. The preparation of [VCl2(H2O)4], [V(H2O)6]Br2 and [V(H2O)6](BF4)2 from vanadium and the appropriate aqueous acid has been confirmed.

Ethanolates and heterocyclic amine complexes of vanadium(II)

Abstract New vanadium(II) alcoholates, VBr 2 ·6EtOH, VCl 2 ·4EtOH and VCl 2 ·2EtOH have been prepared and used with hydrated vanadium(II) salts for the synthesis of vanadium(II) heterocyclic amine complexes. Magnetic and reflectance spectra data show that complexes formulated as [VL 4 X 2 ], where L = a heterocyclic amine, have a distorted octahedral structure whereas complexes of the type [VL 6 ]X 2 have octahedral geometry (X = Cl, Br and I). The amines used in this work were pyrazole (pz), imidazole (iz), 2-methylimidazole (2-miz), benzimidazole (biz) and isoquinoline (iq).

Calorimetric study on the spin-crossover phenomenon between 3T1 and 5E in trans-bis[1,2-bis(diethylphosphino)ethane]diiodochromium(II), [CrI2(depe)2]

Abstract The molar heat capacity of [CrI 2 (depe) 2 ], where depe = trans -bis[1,2-bis(diethylphosphino) ethane], has been measured with an adiabatic calorimeter in the 14–300 K range, and infrared spectra have been recorded at 300 and 91 K in the 4000− ndash ;30 cm −1 range. A sharp heat capacity anomaly arising from the spin-state transition from the low-spin 3 T 1 to the high-spin 5 E electronic ground state was found at 171.45 K. The enthalpy and entropy of the phase transition are Δ trs H = 6686 ± 33 J mol −1 and Δ trs S = 39.45 ± 0.22 JK −1 mol −1 , respectively. The entropy gain can be well accounted for in terms of the contributions from the change in the spin manifold (10%), the change in the metal-ligand skeletal vibrations (~ 75%) and the change in the barrier heights hindering the internal rotation of the eight methyl moieties of the ethyl groups attached to the phosphine ligands (~ 15%). The extremely sharp phase transition observed for this complex has been explained in terms of the large polarizability and thus large compressibility of the iodide ligands. The “cooperativity” often used for spin-crossover phenomena is discussed.

Synthesis and structural studies of complexes of vanadium(II) and vanadium(III) halides with tertiary phosphines

Abstract The vanadium(II) halides [VCl2(H2O)4] and [V(H2O)6]Br2, prepared from the metal and the appropriate acid, combine with 1,2-bis(dimethylphosphino)ethane (dmpe) and 1,2-bis(diethylphosphino)ethane (depe) in methanol to give [VX2(dmpe)2] and [VX2(depe)2] (XCl or Br). The iodo complexes were obtained from [V(MeOH)6]I2, although [VI2(depe)2] was not pure. The complexes [VX2(dppe)2]·2thf (XCl or Br; dppe=1,2- bis(diphenylphosphino)ethane) could not be isolated from methanol, but were obtained from tetrahydrofuran (thf). All are typical vanadium(II) complexes, and [VCl2(depe)2] and [VCl2(dppe)2]·2thf have trans structures. The VCl bond distances, 2.445(2) and 2.420(1) A, respectively, are similar to that in the known complex [VCl2(dmpe)2], but the VP bond distances are longer by approximately 0.06 A and the PVP angles are smaller by c. 3°, possibly due to the steric crowding of the more heavily substituted depe and dppe ligands in the equatorial plane. Some new complexes [VX3(PR3)n] (XCl or Br, PR3=monotertiary phosphine, n=2 or 3) were also prepared from [VX3(thf)3].

Spin isomerism in tris(monothio-β-diketonato)iron(III) complexes

Mossbuer spectral parameters and paramagnetic susceptibilites have been measured for four tris(monothio-β-diketonato)iron(III) complexes. The results are interpreted in terms of a thermal equilibrium between sextet and doublet electronic states. In favourable case, superimposed spectra are observed in which both spin states can be recognised.

Copper(II) and iron(III) complexes of N-nitroso-N- alkylhydroxylamines, and the X-ray crystal structures of bis(N-nitroso-N-isopropylhydroxylaminato)copper(II) and tris(N-nitroso-N-propylhydroxylaminato)iron(III)

Abstract N-nitroso-N-alkylhydroxylamines have been prepared by hydrolysis of the mixture obtained by reaction of nitric oxide with Grignard reagents, and stabilized as their copper(II) or iron(III) complexes, Cu(RN2O2)2 and Fe(RN2O2)3, where R is, for example, Me, Et, Pri, Buiso, Ph, n-C8H17 or n-C12H25. The complexes have been characterized by analytical, magnetic and spectroscopic measurements. By single-crystal X-ray methods Cu(PriN2O2)2 has been found to be trans-planar and Fe(PrnN2O2)3 has a facial octahedral structure; in each complex the NO bond lengths are equal with no significant variation between the copper and iron complexes.

The crystal and molecular structure of bis(1-methyl-1-phenylhydrazine)dichloro-{1-methyl-1-phenylhydrazido(2–)}vanadium(V) chloride, a complex containing two side-on-co-ordinated hydrazine molecules

The complex [VCl2(H2NNMePh)2(NNMePh)]Cl shows simultaneous co-ordination of side-on hydrazine and end-on hydrazide (2–), and forms a tetranuclear structure via an extensive array of hydrogen bonds.

The preparation and characterisation of some complexes of iron(II) with amino acids

Abstract The following complexes of iron(II) with the amino acids glycine, alanine, phenylglycine, phenylalanine, leucine, serine, aspartic acid, glutamic acid, glutamine, tryptophan, histidine, methionine, S-methylcysteine, cystine, and glycylglycine have been isolated: Fe(Gly) 2 , Fe(Ala) 2 , Fe(Phegly) 2 , Fe(Phe) 2 ·2H 2 0, Fe(Leu) 2 ·2H 2 0, Fe(Ser) 2 , Fe(Asp)·2H 2 0, Fe(Glu)·2H 2 0, Fe(Gln) 2 , Fe(Trp) 2 , Fe(His) 2 ·H 2 0 and 2H 2 0, Fe(Met) 2 , Fe(MeCys) 2 , Fe(CysCys) and Fe(GlyGly) 2 . Their magnetic behaviour, reflectance spectra, and Mossbauer parameters are consistent with high spin, hexacoordinate iron(II), and imply extended structures involving carboxylate bridges.

The crystal and molecular structures of a tetraazaannulene and its cobalt(II) complex and the preparation of the chromium(II) complex

The structure sof the diphenyl-substituted tetraazaannulene dptaaH 2 ( 1 ) and its cobalt(II) complex Co(dptaa) ( 2 ) have been determined by X-ray diffraction. The cobalt(II) complex is low spin (μ eff = 2.5 B.M. at 291 K) and except for the two phenyl groups, which are rotated by 30.0° and 38.1° with respect to the CoN 4 plane, the molecule shows less deviation from planarity than the ligand. The chromium(II) complex is low spin(μ eff = 2.85 at 292 K and 2.72 B.M. at 87 K) and could not be obtained as a crystalline form. It is believed to be structurally analogous to Co(dptaa) and not to the related chromium(II) complex Cr 2 (tmtaa) 4 of the tetramethyldibenzotetraaza[14]annulene tmtaaH 2 , which is essentially diamagnetic and contains an unsupported quadruple bond.