Octahedral complexes magnetic, moments

Most Fe complexes are octahedral but several other stereochemistries are known (Table 25.3). [FeX4] (X = Cl, Br, I, NCS) are tetrahedral. A single absorption around 4000 cm due to the T2 E transition is as expected, but magnetic moments of these and other apparently tetrahedral complexes are reported to lie in the range 5.0-5.4BM, and the higher values are difficult to explain. 

Thus the magnetic moments of tetrahedral complexes lie in the range 4.4-4.8 BM, whereas those of octahedral complexes are around 4,8-5.2 BM at room temperature, falling off appreciably as the temperature is reduced. 

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. 

Acetylpyridine thiosemicarbazone forms [Co(8)2Cl2], which is isolated from hot ethanol [178], Based on infrared spectra the pyridyl nitrogen is coordinated and bonding is NS with two chlorines bringing the coordination number to six. The complex is a non-electrolyte in DMF, has a magnetic moment of 4.13 B.M., and the electronic spectrum has bands at about 8160 and 17 860 cm consistent with octahedral stereochemistry. 

Ethanol-dimethoxypropane solutions of either 1-formylisoquinoline or 2-formylquinoline thiosemicarbazone and cobalt(II) salts yield [Co(L)A2] complexes where A = Cl, Br, I, NO3, NCS, or NCSe [147]. All are non-electrolytes, have magnetic moments of 4.30-4.70 B.M. and are five coordinate with approximate trigonal bipyramidal stereochemistry involving NNS coordination based on electronic and infrared spectra. [Co(21-H)2] 2H2O was isolated from a cold methanolic solution of cobalt(II) chloride and 1-formylisoquinoline thiosemicarbazone [187]. Infrared spectral studies show NNS coordination the electronic spectral bands fit a distorted octahedral symmetry, and the magnetic moment is 4.48 B.M. 

Solutions of CrCl2-2CH3CN and the wet solid are extremely sensitive to oxygen. When dried, however, the complex remains unchanged in air for several minutes before oxidation becomes apparent. It is virtually insoluble in acetonitrile but quite soluble in ethanol. The room-temperature magnetic moment (4.8 B.M.) and electronic spectrum are consistent with a high-spin distorted octahedral Cr2+ ion.15... 

The magnetic moment of [Mn(als)2] Oeff=3.96 pB) indicates its Mn(IV) (d3-ty oxidation state. The essentially regular octahedral geometry of this N204 coordinated complex is illustrated in Figure 31.46... 

These Fe(II) complexes are low spin (d6-t2g6), as deducible from their negligible magnetic moment = 0.5 Pb)- In acetonitrile solution they display a chemically reversible Fe(II)/Fe(III) oxidation. It must be taken into account that in acetonitrile solution they possess an octahedral... 

In agreement with an octahedral coordination that has two unpaired electrons (d8-t6geg), the complexes [Nin(bipy)3](C104)2 and [Ni11 (terpy)2][C104]2 possess magnetic moments of 3.20 B and 3.10 respectively. 

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