Chemistry of iron complexes—III. X-ray diffraction,ESR and other spectral studies of new iron(II) and iron(III) complexes with tri-p-tolylarsine oxide

Reactions of iron(II) and iron(III) salts with tri-p-tolylarsine oxide(L) in suitable organic solvents yield complexes of formulas: (i) [FeL₂Cl₂(OH₂)₂] [FeCl₄].2H₂O, [FeL₂Br₂] [FeBr₄].2H₂O; (ii) [Fe(NCS)₃L₂].H₂O; (iii) [FeL(O₂ClO₂)₂(OH₂)] (ClO₄).0.25C₆H₆; (iv) [FeL₃I] [FeI₃].H₂O and (v) [Fe(CO)₃LI]I. Characterization has been done through elemental analyses, IR, far IR, ESR, and reflectance spectra, molar conductance, magnetic moments, t.g.a. and X-ray diffraction (powder) data. The species [FeL₂Cl₂(OH₂)₂]⁺, [FeL₂Br₂]⁺, [Fe(NCS)₃L₂], [FeL(O₂ClO₂)₂OH₂]⁺, [FeL₃I]⁺ and [Fe(CO)₃LI]⁺ have been assigned trans-octahedral, trans-square planar, trans-trigonal bipyramid, trans-octahedral, tetrahedral and cis-trigonal bipyramid structures respectively.     

ESR and spectral studies of bis(ethylenebis(diphenylphosphine))cobalt(II) perchlorate

ESR and reflectance spectra of a low-spin square planar cobalt(II) complex, [Co(dpe)₂](ClO₄)₂ were measured, where dpe represents ethylenebis(diphenylphosphine). Both ESR spectra of diluted in [Ni(dpe)₂](ClO₄)₂ and undiluted samples were of rhombic symmetry, with g₁ = 2.797, g₂ = 2.442 and g₃ = 1.968. Analysis of g- and A-values led to the conclusion that an unpaired electron is in the d_z² orbital in [Co(dpe)₂](ClO₄)₂. The origin of the peak at 11.7 × 10³ cm⁻¹ observed in the reflectance spectrum was elucidated in terms of the ESR parameters and optical spectral data of [Ni(dpe)₂](ClO₄)₂.     

Spectroscopic,magnetic and X-ray powder diffraction studies on U(III) and Np(III) formates

The synthesis of the new Np(III) compound Np(HCOO)₃ is reported and its lattice data, spectroscopic and magnetochemical properties are compared with the refined properties of U(HCOO)₃. Both compounds are isotypic and crystallize in the rhombohedral lattice of Gd(III) formate. The electronic reflectance and IR spectra have been measured and discussed. Low temperature magnetic susceptibilities indicate an antiferromagnetic transition for U(HCOO)₃ at T_N = 12 K. The magnetic moments of 3.70 B.M. (140–300 K) for U(HCOO)₃ and 2.69 B.M. (80–300 K) for Np(HCOO)₃ closely approach the corresponding free ion values.     

Chemistry of iron complexes—IX. I.r. and e.s.r. studies of triisothiocyanatobis(triarylphosphine/arsine oxide) iron(III) and their polynuclear metal complexes with mercury(II) chloride

Summary X-band e.s.r. and i.r. spectra of [Fe(NCS)₃(Ph₃PO)₂](1) and [Fe(NCS)₃(p-Tol₃AsO)₂](2), before and after heating to 100, 150 and 200° C (±2°C), were studied at room temperature. Reactions of (1) and (2) with HgCl₂ in Me₂CO form heteropolymetallic 13 (Fe:hg) complexes: [Fe(NCS)₃(Ph₃PO)₂(HgCl₂)₃]·2Me₂CO (3) and [Fe(NCS)₃(p-Tol₃AsO)₂(HgCl₂)₃]·H₂O (4). Room temperature i.r. and e.s.r. spectra of (3) and (4) have been studied.     

An X-ray investigation on the structure of iron(III) perchlorate solutions

Ferric perchlorate solutions have been investigated by an X-ray scattering technique. The main features of the radial distribution functions are consistent with the presence of ClO₄⁻ ions and of hydrated Fe(H₂O)₆³⁺ complexes in octahedral configuration. Structural parameters have been derived for these two species from the outermost parts of the reduced intensity functions. An hydrogen bonded structure outside the inner coordination sphere of iron(III) is strongly suggested by the presence of a large peak at 4 Å in the radial distribution curves. In this respect a comparison between iron(III) perchlorate and nitrate solutions has made possible to evidentiate a similar structural arrangement for Fe³⁺ ions in both media. Some indications have been also obtained supporting the existence of an outer-sphere FeClO₄ complex and of hydration water around the perchlorate group.     

Porosity of some iron(III), chromium(III), and zirconium(IV) hydroxide oxide xerogels

Porosity and density in water are studied for xerogels prepared by drying iron(III), chromium(III), and zirconium(IV) hydroxide oxide (HO) hydrogels. The hydrogels are either freshly precipitated at pH 7–11 or aged in sodium chloride or sodium sulfate solutions. The space distribution in the xerogels between the volume occupied by the constituent ions and the interstitial volume (spaces between metal-oxygen chains, mesopores, micropores, and macropores) is determined. The meso-and micropore volumes of the chromium(III) HO xerogels are two to four times the volumes of iron(III) and zirconium(IV) HO xerogels. We suggest that the microstructure of the chromium(III) HO hydrogels is almost fully inherited by their xerogels.     

Synthesis and spectral properties of new complexes between glycine and titanium(III), vanadium(III), chromium(III), iron(III), cobalt(II), nickel(II) and copper(II)

Summary Complexes of formula [MCl₃(glyH)₃] (M=Ti, V and Fe) [CrCl₃(glyH)₂H₂O], [MCl₂(glyH)₂(H₂O)₂] (M=Co and Cu) and [NiCl₂(glyH)₃H₂O] have been prepared and characterized by potentiometric curves, chemical analysis, magnetic properties, i.r. and electronic spectral data.     

Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazones: Magnetic,E.s.r. and spectral studies

Summary Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazone (LH) with the general formulae FeLX₂ (X = Cl, Br, NO₃ or SCN) and FeLSO₄ have been prepared and characterised by elemental analysis and by magnetic measurements in the polycrystalline state in the 77–298 K range and by electronic, i.r. and e.s.r. spectra. The FeLX₂ species (X = Cl, NCS or NO₃) are square pyramidal of intermediate spin-state (S=3/2) with an⁴ A ₂ ground state. The magnetic behaviour of FeLSO₄ is commensurate with high order effects coupled with antiferromagnetic exchange interactions. FeLBr₂ is a spin-free dimer involving bromine bridging between two FeLBr₂ square pyramids. However, the low-spin species [FeL(DMF)₃]²⁺ exists in dimethylformamide solution.     

A propanediamine-bridged dinuclear iron(III) complex: Synthesis,X-ray analyses,spectral studies,and magnetic properties

A new propylenediamine-bridged diunclear complex formulated as [Fe₂(Salpn)₃] (I) (pn = 1,2-propylenediamine, H₂Salpn = N,N′-bis(salicylaldehyde)propylenediamine Schiff base) has been prepared from the template synthesis by the reaction of 1,2-propylenediamine with salicylaldehyde in the presence of the iron(III) salt. The metal centers adopt a slightly distorted octahedral geometry, and the Salpn ligands act in both bridging and chelating modes to form a dinuclear complex with the six-membered chelate rings. The magnetic susceptibility investigation for I indicates the presence of very weak antiferromagnetic coupling between the Fe³⁺ cations through the propylenediamine bridge.     

X-ray absorption spectroscopic studies of high-spin nonheme (alkylperoxo)iron(III) intermediates

The reactions of iron(II) complexes [Fe(T(pt-Bu,i-Pr))(OH)] (1a, Tp(t-Bu,i-Pr) = hydrotris(3-tert-butyl-5-isopropyl-1-pyrazolyl)borate), [Fe(6-Me2BPMCN)(OTf)2] (1b, 6-Me2BPMCN = N,N'-bis((2-methylpyridin-6-yl)methyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane), and [Fe(L8Py2)(OTf)](OTf) (1c, L8Py2 = 1,5-bis(pyridin-2-ylmethyl)-1,5-diazacyclooctane) with tert-BuOOH give rise to high-spin FeIII-OOR complexes. X-ray absorption spectra (XAS) of these high-spin species show characteristic features, distinct from those of low-spin Fe-OOR complexes (Rohde, J.-U.; et al. J. Am. Chem. Soc. 2004, 126, 16750-16761). These include (1) an intense 1s --> 3d preedge feature, with an area around 20 units, (2) an edge energy, ranging from 7122 to 7126 eV, that is affected by the coordination environment, and (3) a 1.86-1.96 A Fe-OOR bond, compared to the 1.78 A Fe-OOR bond in low-spin complexes. These unique features likely arise from a flexible first coordination sphere in those complexes. The difference in Fe-OOR bond length may rationalize differences in reactivity between low-spin and high-spin FeIII-OOR species.     

A solid state e.s.r. study of manganese(II) halide-triphenylphosphine oxide complexes

Summary Ph₃PO adducts with manganese(II) halides, viz. MnX₂-(OPPh₃) ₂ (X = Cl or Br) were heated for 1 h and their X-band e.s.r. spectra recorded at room temperature. The chloride adduct, MnCl₂(OPPh₃)₂ completely transformed into the symmetrised product, [Mn(OPPh₃)₄] [MnCl₄] at 175 and 225° C. The bromide adduct, MnBr₂-(OPPh₃)₂, which is probably a mixture of its nonionic and ionic forms at room temperature, showed hyperfine coupling in the g = 2.029 region.     

Visible and near-infrared intense luminescence from water-soluble lanthanide [Tb(III), Eu(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), Er(III)] complexes

The synthesis of a new ligand (1) containing a single phenanthroline (phen) chromophore and a flexibly connected diethylenetriamine tetracarboxylic acid unit (DTTA) as a lanthanide (Ln) coordination site is reported [1 is 4-[(9-methyl-1,10-phenantrol-2-yl)methyl]-1,4,7-triazaheptane-1,1,7,7-tetraacetic acid]. From 1, an extended series of water-soluble Ln.1 complexes was obtained, where Ln is Eu(III), Tb(III), Gd(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III). The stoichiometry for the association was found 1:1, with an association constant K(A) > or = 10(7) s(-1) as determined by employing luminescence spectroscopy. The luminescence and photophysical properties of the series of lanthanide complexes were investigated in both H2O and D2O solutions. High efficiencies for the sensitized emission, phi(se), in air-equilibrated water were observed for the Ln.1 complexes of Eu(III) and Tb(III) in the visible region (phi(se) = 0.24 and 0.15, respectively) and of Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III) in the vis and/or near-infrared region [phi(se) = 2.5 x 10(-3), 5 x 10(-4), 3 x 10(-5), 2 x 10(-5), 2 x 10(-4), 4 x 10(-5), and (in D2O) 4 x 10(-5), respectively]. For Eu.1 and Tb.1, luminescence data for water and deuterated water allowed us to estimate that no solvent molecules (q) are bound to the ion centers (q = 0). Luminescence quenching by oxygen was investigated in selected cases.