Iron complexes magnetic moments

Fe " complexes in general have magnetic moments at room temperature which are close to 5.92 BM if they are high-spin and somewhat in excess of 2BM (due to orbital contribution) if they are low-spin. A number of complexes, however, were prepared in 1931 by L. Cambi and found to have moments intermediate between these extremes. They are the iron(lll)-A,A-dialkyldithiocarbamates, [Fe(S2CNR2)3], in which the ligands are ... 

This simple explanation accounts quite well for a variety of dithiocarbamato complexes of iron(III) whose magnetic moments rise gradually from about 2.3 BM (corresponding to low-spin d ) at very low temperatures to > 4BM (corresponding to roughly equal populations in the two states) above room temperature. 

Molybdenum hexafluoride. 3,1412 Molybdenum-iron-sulfur complexes, 4,241 Molybdenum oxide amino acid formation prebiotic systems, 6, 872 Molybdenum storage protein microorganisms, 6, 681 Molybdenum telluride, 3, 1431 Molybdenum tetraalkoxides physical properties, 2, 347 Molybdenum tribromide, 3,1330 Molybdenum trichloride, 3,1330 Molybdenum trifluoride, 3, 1330 Molybdenum trihalides, 3, 1330 bond lengths, 3, 1330 magnetic moments, 3,1330 preparation, 3,1330 properties, 3, 1330 structure, 3,1330 Molybdenum triiodide, 3,1330 Molybdenum trioxide complexes, 3, 1379 Molybdenum triselenide, 3, 143)... 

The ruthenium compounds are entirely analogous to the iron compound. A profitable discussion of more of the numerous complexes containing NO can be given only after further experimental data, especially relative to magnetic moments, have been collected. 

By way of example, a d iron(iii) complex with a magnetic moment close to 1.73 must, by reference to Fig. 5-1, be low-spin with A ct >P since an iron(iii) complex with Aoct < P would have a magnetic moment of 5.92. 

Fig. 1. Plot of effective magnetic moment vs. iron-sulfur bond length in [FeCRidtcls] complexes.

There have been no reports of complexes of " JV-substituted thiosemicarbazones derived from 2-formylpyridine, but 2-acetylpyridine JV-methyl-thiosemicarbazone, 3a, formed [Fe(3a-H)2]C104 and [Fe(3a-H)2]FeCl4 [117]. The nature of these two species was established by partial elemental analyses, molar conductivities, magnetic moments, electronic, infrared, mass and electron spin resonance spectra. A crystal structure of a related selenosemicarbazone complex confirmed the presence of a distorted octahedral iron(III) cation coordinated by two deprotonated anions so that each ligand is essentially planar and the azomethine nitrogens are trans to each other the pyridyl nitrogen and selenium donors are both cis. 

Complexes of 2-formylquinoline and 1-formylisoquinoline thiosemicarbazones, 20 and 21, respectively, have been prepared, but iron(III) complexes were not included in the initial study [147], More recently [132], an iron(III) complex of 1-formylisoquinoline thiosemicarbazone, [Fe(21)Cl3] has been found to have a magnetic moment of about 2.1, g of 2.146, and involve the neutral ligand bound in a tridentate manner. A complex of the same stoichiometry was reported for 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone, 22. Its magnetic moment is about 2.1 and g, = 2.126. 

THF solution [290]. There had been much confusion in the past about the magnetic moment of the iron(I) species and the correct Mossbauer and NMR properties caused by impurities of the samples and possible unknown axial ligation. However, with clean crystallized samples with known molecular structure [291], the first reduction product of iron(II)(tetraphenylporyphrin), [Fe(TPP)], can be clearly characterized as a quasiplanar iron(I) complex with spin S = 1/2 (EPR = 2.28,... 

Barefield, Busch and Nelson (1968) Iron, cobalt and nickel complexes having anomalous magnetic moments [202]. 

Several interesting features of the magnetic properties of [Fe(HB(pz)3)2] are revealed in Fig. 1. First, between 78 and ca. 295 K the magnetic moment is not zero, as might be expected for a diamagnetic compound, but rather increases slightly from a moment of ca. 0.6 jUb at 78 K. This non-zero moment is typical of low-spin iron(II) complexes, and is a consequence of sec-... 

The inverse magnetic susceptibility and the effective magnetic moment, jueff, of [Fe(HC(3,5-(CH3)2pz)3)2](BF4)2 are shown in Fig. 16 where it is immediately obvious that the magnetic properties of this complex are quite unusual [46]. Above ca. 210 K the eff of ca. 5.0 is clearly that expected of a high-spin iron(II) complex. But below ca. 190 K the moment decreases to a substantially lower value of ca. 3.7 /uB. Further, at ca. 90 K there is a small irreversible change in susceptibility and moment, a change that is associated with crystal reorientation in the applied field. The reason for the abrupt decrease in the moment at ca. 200 K to ca. 3.7 becomes apparent from a study of the Mossbauer spectra of [Fe(HC(3,5-(CH3)2pz)3)2](BF4)2. 

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