Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination

The physical interaction of gases with crystalline solids: I. Gas-solid energies and properties of isolated adsorbed atoms☆

Zero-field splitting in metal complexes

1 – Optical Spectra and Electronic Structure of Porphyrins and Related Rings

High H2 adsorption by coordination-framework materials

Intermediate-spin (S = 3/2) porphyrinatoiron(III) complexes

The preparation of the square planar complex octaethylporphyriniron(II), fe(OEP), is reported. As in tetraphenylporphineiron(II) and phthalocyanineiron(II). the ferrous ion in fe(OEP) appears to be in the intermediate spin (S = 1) state. The hexacoordinate adducts of Fe(OEP) with pyridine, ammonia. 3and 4-picoline are all diamagnetic. Mossbauer spectra have been measured between 4.2 and 300 K, and in applied magnetic fields of up to 50 kG. In every case the quadrupole coupling constant is positive and the electric field gradient at iron is axially symmetric. The nearly temperature-independent quadrupole splitting in Fe(OEP) suggests there are no low-lying excited orbital states in this complex. Comparisons of the Mossbauer parameters reported here with data for related ferrous porphyrin and phthalocyanine complexes provide insight into the (J' and 1l' bonding characteristics of the tetradentate ligands. Synthetic iron porphyrins of unusual coordination or oxidation state are of interest both from the preparative point of view and as regards the detailed electronic structure of the central metal ion and their relationship to biological function. Since in most cases electron spin resonance cannot be observed in ferrous complexes, Mossbauer spectroscopy offers the only direct method of obtaining such structural details of the iron atom in ferrous prophyrins. Owing to the difficulty in isolating ferrous porphyrins in the solid state, few applications of Mossbauer spectroscopy to such systems have been reported to date. Epstein et al.I studied some hexacoordinate adducts of the type FeLX2, where L was either protoporphyrin IX (PP) or meso-tetraphenylporphine (TPP), and X = pyridine (py), piperidine (pip), and imidazole (im). Only Fe(TPP)(piph was isolated and characterized, the her complexes being studied as frozen solutions. Fe(TPP), I, was the first example of a ferrous porphyrin to be isolated in the solid state without additional ligands in the axial coordination sites, and its preparation was reported independently by two groups.2,3 Kobayashi et al. 4 have studied Fe(TPP) and its bis adducts with tetrahydrofuran (THF) and pyridine in the solid state. using Mossbauer and susceptibility measurements. These authors4 and Husain and Jones5 reported a magnetic moment of about 4.7 JlB for Fe(TPP), and have assumed that the ferrous ion has a high-spin (s , 2) ground state. These results are not in agreement with the recent work of Collman et al.,6 who found the moment to be 4.4 JlB. On the basis of Mossbauer and x-ray crystallographic data the latter authors6 have shown that the ferrous ion in Fe(TPP) is in the rare intermediate-spin (5 = 1) state. The Mossbauer isomer shift at room temperature is 0.42 mmls (relative to metallic iron), and the quadrupole splitting is 1.52 mmls and independent of temperature. The x-ray data indicate that the iron(ll) and the four porphinato nitrogen atoms are coplanar. Kobayashi et al.4 have assigned an intermediate-spin ground state to iron in Fe(TPP)(THFh, but there is considerable doubt that this was the actual compound studied by them. In addition to the poor analytical data given in ref 4, the quoted room temperature magnetic moment (2.75 JlB) is very different from that reported for this complex by Collman and Reed3 (5.1 JlB). Moreover, in view of the facile oxidation of Fe(TPP) derivatives and recent Mossbauer data for several oxo-bridged ferric porphine dimers,7 we suspect that the compound studied4 was in fact Jl-O[Fe(TPP)lz. However, there is agreement24 that Fe(TPP)(pyh contains low-spin (S = 0) iron(ll), as does6 Fe(TPP)(piph, Only two tetracoordinate ferrous porphyrin complexes other than Fe(TPP) have been reported: the so-called \"picket-fence\" porphyrin tetra(a,a,a,a-orthopivalamide)phenylporphineiron( II)810 and octamethyltetrabenzporphyriniron(II) II (Fe(OTBP), 2). The former complex contains6 high-spin

Synthesis and Moessbauer spectra of octaethylporphyrin ferrous complexes

Organotin carboxylates I. Mösssbauer and infrared study of triphenyltin carboxylates and the novel compounds RSn(O)OCOR

Trifluoromethylsulfonates of tin

Cu(py) 4 (CF 3 SO 3 ) 2 cristallise dans le systeme orthorhombique, groupe d'espace Pbcn et sa structure est affinee jusqu'a R=0,046. Coordinat pseudooctaedrique deforme autour de Cu

Pyrazine and pyridine complexes of copper(II) trifluoromethanesulfonate. Crystal structure of tetrakis(pyridine)bis(trifluoromethanesulfonato-O)copper(II) and magnetic exchange in (pyrazine)bis(trifluoromethanesulfonato-O)copper(II)

John R. Sams

Papers

Intermediate-spin (S = 3/2) porphyrinatoiron(III) complexes

Synthesis and Moessbauer spectra of octaethylporphyrin ferrous complexes

Organotin carboxylates I. Mösssbauer and infrared study of triphenyltin carboxylates and the novel compounds RSn(O)OCOR

Trifluoromethylsulfonates of tin

Pyrazine and pyridine complexes of copper(II) trifluoromethanesulfonate. Crystal structure of tetrakis(pyridine)bis(trifluoromethanesulfonato-O)copper(II) and magnetic exchange in (pyrazine)bis(trifluoromethanesulfonato-O)copper(II)