Antony B. Blake

Crystal structure and mass spectrum of µ3-oxo-hexakis(µ-trimethyl-acetato)-trismethanoltri-iron(III) chloride, a trinuclear basic iron(III) carboxylate

The crystal structure of the title compound has been determined by single-crystal X-ray diffraction photography, and refined isotropically by the method of least squares to R 0·11 6, based on 552 independent reflections. There are two molecules in a hexagonal unit cell, space group P63, with a= 10·43(3) and c= 22·79(5)A. The structure consists of cations [Fe3O(piv)6(MeOH)3]+(piv = CMe3·CO2) lying on the three-fold axes, with chloride ions on the screw axes. The cation is analogous to that in the chromium(III) and iron(III) basic acetates, except for the rigorous three-fold symmetry and the fact that the central oxygen atom is displaced 0·24 A from the Fe3 plane. The mass spectrum is unusual in showing peaks due to ions containing more than three iron atoms, e.g. Fe4O(piv)6+ which appears in greater abundance than any trinuciear ion.

Magnetic properties of binuclear manganese(II), cobalt(II), nickel(II) and copper(II) complexes of a macrocyclic ligand derived from pyridine-N-oxide, and crystal structure of the nickel complex

Abstract The preparation of complexes M 2 L ( NO 3 ) 4 ·2 CH 3 OH ·n H 2 O ( 4a-d ) (M = Mn, Co, Ni, Cu; L = C 18 H 22 N 6 O 4 ( 3 ); n = 0.5 or 1) from pyridine-1-oxide-2,6-dialdehyde, 1,2-diaminoethane and the metal(II) nitrate is reported. The complex [Ni 2 L(H 2 O) 4 ](NO 3 ) 4 · 2H 2 O ( 5 ) was also prepared and its crystal structure determined. 5 is monoclinic, space group P2 1 /n, a = 11.831(8), b = 12.168(8), c = 12.329(7) A , β = 114.26(5)°, Z = 2 . In the cyclic ligand 3 , the pyridine-1-oxide rings are linked by CH(OH).NH.(CH 2 ) 2 .N:CH groups, showing that partial hydrolysis of the expected Schiff-base ligand has occurred during synthesis of the complex. In the centrosymmetric complex 5 , the Ni 2+ ions are bridged in a planar Ni 2 O 2 unit by the N-oxide oxygen atoms, the ligand adopting a non-planar ‘stepped’ conformation with pyramidal stereochemistry at the bridging O atoms. Six-fold coordination of each Ni 2+ ion is completed by two N atoms and two cis water molecules. The magnetic susceptibilities of 4a-d were measured between 5 and 300 K and analysed to obtain values of the parameter J in the exchange Hamiltonian −2 J S 1 ·S 2 : J = - −1.15, −5.0, −15.5 and +3.3 cm −1 , respectively. These values are discussed in terms of the contributing orbital pathways.

Magnetic and spectroscopic properties of some heterotrinuclear basic acetates of chromium(III), iron(III), and divalent metal ions

Reaction of Fe3+, M2+, and acetate ions in aqueous solution gives [FeIII2MIIO(MeCO2)6(H2O)3]·3H2O (M = Mg, Mn, Co, Ni, or Zn), which on crystallisation from pyridine (py) is converted into [FeIII2MIIO(MeCO2)6(py)3]. Reaction of chromium(II) acetate with metal(II) acetate in pyridine in the presence of air gives [CrIII2MIIO(MeCO2)6(py)3](M = Mg, Co, or Ni), and with [FeIII2MIIO-(MeCO2)6(py)3] in pyridine inthe absence of air gives [CrIIIFeIIIMnIIO(MeCO2)6(py)3](M = Mn or Fe) and [CrIII2FeIIIO(MeCO2)6(py)3]. The compounds with co-ordinated pyridine have been examined crystallographically and magnetically. The Cr2Mg, Cr2Ni, Fe2Ni, and CrFeNi compounds crystallise in the monoclinic system, space group Cc or C2/c, Z= 4, but the other seven compounds are rhombohedral and isomorphous with [M3O(MeCO2)6(py)3]·py (M = Mn or Fe), indicating that the three metal atoms are crystallographically equivalent as a result of disorder in the molecular orientation. Powder magnetic susceptibilities for the Cr2Co and Cr2Ni compounds(4.2–60 K), for the Fe2Mn and Fe2Ni compounds (4.2–295 K), and for the Fe2Ni(aquo) and Fe2Mg compounds (80–295 K) have been fitted by use of an exchange Hamiltonian to yield values of the exchange parameters J for the Cr–Cr, Fe–Fe, Cr–Ni, Fe–Ni, and Fe–Mn interactions, which are discussed in terms of superexchange mechanisms. The values of JFeFe in the Fe2Mg, Fe2Mn, and Fe2Ni compounds and of JCrCr in the Cr2Co and Cr2Ni compounds are approximately twice their values in the cations [MIII3O(MeCO2)6(H2O)3]+(M = Cr or Fe), indicating that the µ3-O atom provides the main super-exchange pathway. Diffuse-reflectance and solution spectra (6 000–40 000 cm–1) of the compounds have been recorded at room temperature and are discussed in terms of the ligand-field model; a band in the spectra of the FeIII2FeII and CrIIIFeIIIFeIII compounds at ca. 7 000 cm–1 is assigned to intervalence transfer. The room-temperature spectra of [M3O(MeCO2)6L3]Cl (M3= CrIII3, CrIII2FeIII, CrIIIFeIII2 or FeIII3; L = H2O or py) have also been obtained, and intense absorption bands at ca. 19 000 and 26 000 cm–1 are tentatively assigned to simultaneous (Cr3+, Fe3+) double excitations.

Crystal structure and magnetic properties of a binuclear triketonate complex of five-co-ordinate copper(II) : bis[heptanetrionato(2–)]bis-pyridinedicopper(II)

The crystal and molecular structures of the title compound have been determined by single-crystal X-ray diffraction photography. The structure was solved by Patterson and Fourier methods and refined anisotropically by the method of least squares to R 11·1 % for 1743 visually estimated observed reflections. The black crystals are triclinic, space group P, and the reduced unit cell, of dimensions a= 9·60, b= 9·94, c= 8·61 (±0·03)A, α= 123·7, β= 91·6, γ= 108·2 (±0·3)°, contains one centrosymmetric binuclear molecule. The triketonate ligands are terdentate, with the central O atoms linking the Cu atoms to give a planar Cu2O2 ring with angles Cu–O–Cu 103 and O–Cu–O 77°. Each copper atom is bonded to four coplanar O atoms and a pyridine N atom in a square-pyramidal arrangement, with Cu–O 1·93 (mean) and Cu–N 2·32 A, the two pyridine ligands being on opposite sides of the molecule. The effective magnetic moment per Cu falls from 0·75 at 335 to 0·0 B.M. at 87 K; the magnetic data are consistent with intramolecular exchange giving a singlet–triplet separation 2|J| 690 cm–1, with g 2·09.

Mesogenic properties of copper(II) complexes formed from α-substituted β-dialdehydes and β-diketones

The relationship between molecular structure and mesogenic properties is explored for copper(II) complexes of α-substituted β-dialdehydes and β-diketones. The copper(II) complex of p-pentylphenylmalonaldehyde shows a nematic phase, but the presence of off-axial substituents or the removal of the aromatic ring precludes mesophase formation.

Reactions of bis(η-cyclopentadienyl)nickel with some pyrazoles. Unusual temperature dependence of the hydrogen-1 nuclear magnetic resonance spectrum of the cyclopentadienyl group

Bis(η-cyclopentadienyl)nickel reacts with 3,5-dialkylpyrazoles in benzene to give dark red diamagnetic complexes [{Ni(η-C5H5)(N2C3HR2)}2](R = Me, Et, or Pri). No reaction occurs when R = But. The position of the resonance of the η-C5H5 group in the 1H n.m.r. spectrum is temperature dependent, moving ca. 1 p.p.m. upfield between 0 and 80 °C; this behaviour is consistent with an equilibrium (ΔHca. 45 kJ mol–1) between the dimer and a paramagnetic monomer. The reaction of [Ni(η-C5H5)2] with pyrazole and with 3-methylpyrazole results in the displacement of both η-C5H5 groups and the formation of polymeric bis(pyrazolates).

Heterotrinuclear basic acetates containing chromium(III), iron(III), and a divalent metal: spectroscopic consequences of Metal–Metal interactions

Complexes [CrIII2MIIO(MeCO2)6py3](M = Mg, Fe, Co, Or Ni) and [CrIIIFeIIIMIIO(MeCO2)6py3](M = Mn, Fe, Co, or Ni; py = pyridine) are reported; their absorption spectra, together with those of the analogous Fe2IIIMIIcomplexes, provide new information about electronic properties of the M3O system.

Structure-mesophase relationships in dialdehyde and related complexes of copper(II) and oxovanadium(IV)

Abstract Copper(II) and oxovanadium(IV) complexes of a new series of α-substituted β-dialdehydes have been synthesised, and their mesophase properties studied. Bis(4-alkyloxyphenylmalonaldehyde)copper and bis(4-alkylphenylmalonaldehyde)copper complexes show a narrow (10 °C) nematic phase below their cleaning temperatures. The oxovanadium(IV) complex of a ligand generally has a lower melting point than its copper analogue, but often does not show the liquid crystal phase shown by the copper analogue. Introduction of a single methyl group in place of an aldehyde proton is sufficient to destroy liquid crystal properties.

Crystal structure of an eight-co-ordinate manganese complex: bis-(3,4-di-2-pyridylpyridazine)dinitratomanganese(II)

The crystal and molecular structures of the compound [Mn(dppn)2(NO3)2](dppn = 3,6-di-2-pyridylpyridazine) have been determined by single-crystal X-ray diffraction photography, and refined anisotropically by the method of least squares to R 6·6% for 1816 independent observed reflections. The yellow crystals are triclinic, and the unit cell, of dimensions a= 8·88, b= 11·95, c= 14·20 (±0·03)A, α= 107·0, β= 87·6, γ= 103·0 (±0·3)°, contains two enantiomorphous molecules. All four ligands are bidentate, giving an eight-co-ordinate complex roughly approximating to C2 symmetry. The dppn molecules are nearly planar, and the two non-co-ordinating N atoms in each ligand are mutually trans. The four Mn–N bond lengths are all close to 2·30 A. The co-ordination of one nitrate ion is symmetrical (Mn–O 2·46 A), that of the other is unsymmetrical (Mn–O 2·30 and 2·47 A). This compound and its cadmium analogue are isomorphous. The i.r. spectra in the region of nitrate vibrations are reported.

Determination of the local environment of the metals in [CrIII2CoIIO(MeCO2)6(py)3]·py (py = pyridine) by chromium and cobalt K-edge extended X-ray absorption fine structure. Geometric and charge-polarisation influences on Cr–O–Cr superexchange

X-Ray absorption spectra at the chromium and cobalt K edges have been recorded for the metal-disordered compound [CrIII2CoIIO(MeCO2)6(py)3]·py (py = pyridine) and the associated extended X-ray absorption fine structure (EXAFS) analysed using curved-wave theory with the inclusion of multiple scattering for the co-ordinated pyridine and acetate groups; a corresponding study for the iron K-edge EXAFS of [Fe3O(MeCO2)6(py)3]·py was accomplished as a calibrant of the interpretive procedure. The dimensions Cr–µ3-O 1.87, Co–µ3-O 1.95, Cr–O (acetate) 1.98, Co–O (acetate) 2.09, Cr–N 2.26, Co–N 2.24, Cr ⋯ Cr 3.30 and Cr ⋯ Co 3.28 A were obtained from the analysis of the EXAFS, with good agreement between the values of the Cr ⋯ Co distance obtained independently from the analyses of the chromium and cobalt EXAFS. The metal–ligand and –metal distances are in good agreement with crystallographic data on related compounds. The difference in the Cr–µ3-O and Co–µ3-O distances indicates that the central (µ3) oxygen atom is slightly displaced (ca. 0.05 A) from the centre of the metal triangle, away from the CoII and towards the point midway between the two chromium(III) atoms. Such a structural change and the increased electron density of the central oxygen combine to produce a marked increase in the CrIII–O–CrIII superexchange and a reduced ligand field at the chromium(III) sites, for the Cr2CoO system as compared with CrIII3O analogues.