Nitrogen paramagnetism

The product is a black-brown solid that is very sensitive to oxygen. The same cation can be obtained by oxidation of S4N4 with AsFs and is unusual in being the only sulfur-nitrogen (paramagnetic) radical that has been obtained as a stable crystalline salt. X-ray diffraction analysis shows the structure to be a planar 5-membered ring with approximate... 

Paramagnetism implies the presence of single, unpaired, electrons. Hence nitrogen oxide is paramagnetic and so is any other molecule or ion containing unpaired electrons. If the total number of electrons in an ion or molecule is odd. then it must be paramagnetic but some molecules (e.g. Oj and ions have an even number of electrons and yet are paramagnetic because some of them are unpaired. 

The structure of nitrogen dioxide contains an unpaired (odd) electron and the molecule is consequently paramagnetic. The odd electron is not localised on any atom and the structure can be best represented as a resonance hybrid of the structures ... 

Gaseous nitrogen dioxide is a brown, paramagnetic, non-flammable, toxic, strongly oxidizing, coiTosive substance shipped in approved, low-pressure steel cylinders. It is prepared in situ by heating lead nitrate ... 

EPR studies of S-N radicals were reviewed in 1990. Many radicals containing the S-N linkage are persistent for more than several hours in solution at room temperature. Perhaps the best known example is the nitrosodisulfonate dianion [0N(S03)] , named as Fremy s salt. In the solid state this radical dianion dimerizes through weak N 0 interactions, but it forms a paramagnetic blue-violet monomer in solution. Although most chalcogen-nitrogen radicals dimerize in the solid state, a few heterocyclic C-S-N systems can be isolated as monomers (Section 11.3). 

Numerous charged sulfur-nitrogen species have been synthesized in recent years, particularly those having an odd number of N atoms which would otherwise be paramagnetic. However, thio analogues of nitrites (N02, p. 461) and nitrates (N03, p. 465) are unknown. 

The Lewis structures of the oxides of nitrogen are shown in Figure 21.6. Two of these species, NO and NO are paramagnetic, with one impaired electron. When nitrogen dioxide is cooled, it dimerizes the unpaired electrons combine to form a single bond between the two nitrogen atoms ... 

Formylthiophene thiosemicarbazone, 26, forms [Co(26)2A2]A and [Co(26)A3(H20)] (A = Cl, Br, I, NO3, and OAc), by varying the preparative hgand to cobalt(II) salt mole ratio in hot ethanol [201]. Addition of sodium hydroxide allows isolation of [Co(29-H)3]. All complexes are weakly paramagnetic indicating spin paired complexes. Spectroscopic studies showed bonding via the azomethine nitrogen and thiol sulfur, but not the thiophene sulfur. 

Reduction of both nickel porphyrins and thiaporphyrins to Ni1 species has been studied by EPR and 2H NMR spectroscopy.179, 2 58 The Ni1 complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin has been isolated and characterized. Reaction of this complex with sulfur dioxide produced a paramagnetic five-coordinated Ni1 S02 adduct, while reaction with nitrogenous base ligands (amines, pyridines, imidazoles) yielded five- and six-coordinate complexes. In addition, the crystal structure of Ni1 diphenyldi-p-tolyl-21-thiaporphyrin has been determined. The coordination geometry about the nickel center is essentially square planar with extremely short Ni—N and Ni—S bonds (Ni—N = 2.015(2) A, 2.014(12) A, and 1.910(14) A and Ni—S = 2.143(6) A).2359... 

As can be seen from Table 1, not only the spectral data are quite different between pairs of compounds, but also the paramagnetism is decreasing when the carbon atom attached to the nitrogen is replaced by silicon, all other atoms being equal. As we have not been able to determine the molecular structures of the compounds until now, we cannot ascribe the change in properties to a definite change in structure. Nevertheless it seems obvious that the carbon or silicon atom in 6-position to the metal must have an important impact on the orbital-splitting at the transition element. 

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