Bruce W. Dockum

On the nature of the spin ground state of iron(II) in Fe(2,9-di-CH3-phenanthroline)2(NCS)2

Abstract The temperature dependence of the zero field Mossbauer spectrum and magnetic susceptibility of Fe(2,9-di-CH3-phenanthroline)2(NCS)2 over the range 1.8 to 300 K shows that the complex contains spin quintet iron(II) at all temperatures. The ligand is apparently to the weak field side of the ‘crossover point’ and contrary to the results of a previous study there is no evidence of a transition to a lower multiplicity (triplet or singlet) ground state. The observed decrease of the magnetic moment (4.81 μβ at 302 K to 3.48 μβ at 1.82 K) is consistent with zero field splitting (|D|≈ 5 cm−1) of the ground spin manifold.

On the existence of tris 2,2'-biquinoline complexes of first transition series metal ions in the solid state. Spectra and magnetic characterization of [Fe(II)(2,2'-biquinoline)3](NCS)2 and some related pseudo-tetrahedral ferrous compounds

Abstract Double benzo substitution cis to the nitrogen atoms of 2,2′-bipyridine results in 2,2′-biquinoline, hereafter, biq. Numerous examples of tris 2,2′-bipyriidne metal species are known, but to out knowledge, there have been no previous reports of tris biq metal species. Herein, we report the first isolation of what appears to be a tris biq species, Fe(biq) 3 (NCS) 2 , in the solid state obtained from a water-acetone solution as an analytically pure, pale blue-gray solid. Zero and high field Mossbauer, optical (near infrarcd-visible), and infrared spectra as weil as cryomagnetic data clearly show that Fe(biq) 3 (NCS) 2 contains a pseudo-octahedral high spin iron(II) chromophore. Several possibilities are proposed for the structure of Fe(biq) 3 (NCS) 2 including some with unidentate biq. The weak field, highly hindered environment of the complex is such that it readily undergoes facile loss of two moles of ligand simply on mixing the solid complex with a variety of organic solvents. The resulting neutral buff-colored iron(II) complex, Fe(biq)(NCS) 2 , is a pseudo-tetrahedral monomer which can also be prepared by the direct reaction of an ethanolic solution of Fe(NCS) 2 with a benzene solution of biq in a 1:1 stoichiometry. The spectral and cryomagnetic properties of Fe(biq)- (NCS) 2 as well as those for the related pseudo-tetrahedral compounds Fe(biq)Cl 2 , Fe(2,9-dimethyl-l,10-phenanthroline)X 2 (X=CI - , Br - , I - , NCS - ) and Fe(2,9-dimethyl-4,7-di-phenyl- 1,10-phenanthroline)Cl 2 , are reported as weil. In particular, the latter pseudo-tetrahedral systems are found to exhibit a novel, complex range of slow paramagnetic behavior depending on T , H o and specific coordinated anion. This behavior correlatcs with low temperature susceptibility data.

Magnetic susceptibility and high field Mössbauer effect studies of some spin triplet iron (IV) compounds

Mossbauer spectra of some spin triplet iron (IV) compounds with dithiocarbamate ligands have been observed in large magnetic fields at low temperatures. The magnetic and electric hyperfine interactions agree with the model put forth by Oosterhuis and Lang to explain the action of low symmetry crystal fields on a t42g electronic configuration. A trigonal distortion together with the spin–orbit interaction in a perturbation theory treatment is used as a model and gives the spin Hamiltonian parameters D, ?, ?, (efg), which simulate the data fairly well. The electric field gradient does vary with temperature while the paramagnetic interactions are essentially temperature independent in contrast to the behavior previously observed in tetragonal Fe(IV) arsine complexes. The temperature (1.6–300 K) and field dependence of the susceptibility of one of these salts Fe(diethyldithiocarbamate)3(BF4) has also been studied using the Faraday method giving a value of D=23.8 cm−1 from least square fitting consistent with ...

A high field mössbauer study of a six coordinate iron II dithiocarbamate complex and comparison of the Fe(II)S6, Fe(III)S6 and Fe(IV)S6 chromophores in tris (diethyldithiocarbamate) complexation

Abstract Mossbauer spectroscopy shows that the quadruple interaction in tris (N, N′-diethyldithiocarbamate) iron II is negative, axially symmetric and that the compound is rapidly relaxing at 4.2 K. The results indicate a 5 A ground term arising from trigonal compression of a Fe(II)S 6 chromophore and positive zero field splitting. A correlation is made with data for the Fe(III)S 6 and Fe(IV)S 6 tris-diethyldithiocarbamates.

Low temperature magnetic behavior of some polymeric divalent copper complexes of common endo-bidentate ligands

Abstract The temperature dependences of the molar magnetic susceptibility of powder samples of Cu(ethylenediamlne)Cl 2 , Cu(ethylenediamine)(NCS) 2 and the corresponding mono-2,2′-bipyridyl analogues have been determined over the range 1.2 to 300K. All four systems exhibit weak antiferromagnetic exchange such that their Neel temperatures are

Magnetic superexchange involving the oxygen-sulfur-oxygen pathway of the sulfate ion: A Mössbauer spectroscopy and magnetic susceptibility study of Fe(2,9-di-CH3-phenanthroline) SO4

Abstract Zero-field Mossbauer spectra of powder samples of Fe(2,9-di-CH 3 -phenanthroline) SO 4 over the range 1.7 to 300°K show a large (∼ 3.6 mm/sec) temperature-independent quadrupole splitting corresponding to an orbital singlet ground term. The chemical isomer shift, δ FE=O , is 1.16 mm/sec (source and absorber at 4.2°K) corresponding to six coordinate high-spin iron (II). Below 4.2°K, the compound exhibits magnetic hyperfine splitting suggesting slow relaxation and the possibility of long-range three-dimensional magnetic ordering with a critical temperature T c such that 3.5°K T c H n = 325 kG at 1.69°K. High-field Mossbauer spectra at 300°K indicate that the principal component of the electric field gradient tensor is positive and axial. Similar spectra at 4.2°K show an absence of nuclear Zeeman splitting for applied fields up to 60 kG, and indicate that at 4.2°K the material is rapidly relaxing but with substantial magnetic polarization and a negative internal hyperfine field. The temperature dependence of the magnetic susceptibility confirms antiferromagnetic interactions with a broad maximum χ ′ M at ∼ 11.8°K presumably due to low-dimensionality exchange interactions (possibly one) along M OSO M chains. Least-squares fits of χ ′ M −1 versus T for T 50°K indicate (Curie-Weiss behavior with C = 3.26 emu/mole, θ = -21.95°K, and μ eff = 5.11.

Low temperature magnetic properties and molecular structure of Cu(2,2′-bipyridine)2(NCS)2

Abstract The temperature and field dependence of the magnetic susceptibility of Cu(2,2′-bipyridine) 2 (NCS) 2 have been determined over the range 2–100 K using the Faraday method. The magnetic results in conjunction with IR spectra are inconsistent with a previous formulation of the compound as a thiocyanate bridged dimer but rather support a monomeric pseudo-octahedral structure, [Cu(2,2′-bipyridine) 2 (NCS) 2 ], containing magnetically isolated cupric ions exhibiting essentially Curie law behavior.