Azomethine nitrogen

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. 

The S-methyldithiocarbazates of both 2-picolylphenylketone, 16, and 2,6-luti-dylphenylketone, 17, yielded high spin iron(Ill) complexes, [Fe(15-H)Cl2(H20)] and [Fe(16-H)Cl2(H20)] [144]. Both complexes involve a tridentate ligand bonding via the pyridyl nitrogen, azomethine nitrogen and thiol sulfur. 

Iron(III) complexes of 2-acetylpyridine Af-oxide iV-methyl- and 3-azabicyclo[3.2.2.]nonylthiosemicarbazone, 24 and 25, respectively, have been isolated from both iron(III) perchlorate and chloride [117], The perchlorate salt yields low spin, octahedral, monovalent, cationic complexes involving two deprotonated, tridentate thiosemicarbazone ligands coordinated via the N-oxide oxygen, azomethine nitrogen and thiol sulfur based on infrared spectral studies. Their powder ESR g-values are included in Table 1 and indicate that bonding is less covalent than for the analogous thiosemicarbazones prepared from 2-acetylpyridine, 3a and 4. Starting with iron (III) chloride, compounds with the same cations, but with tetrachloroferrate(III) anions, were isolated. 

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

Iron(II) complexes are often included in studies when complexes are prepared from a large number of different metal ions. 2-formylpyridine thiosemicarbazone, 5, forms brown [Fe(5)2A2] (A = Cl, Br) when prepared in ethanol and [Fe(5-H)2] from aqueous alcohol solution [156], All of these complexes are diamagnetic. The resonance Raman and infrared spectra of [Fe(5-H)2] were examined in detail [130] and coordination occurs via the pyridyl nitrogen, azomethine nitrogen and thiol sulfur. There is appreciable d-d sulfur-to-iron(II) Jt-bonding. Solution studies of iron(II) complexes of some 5-substituted-2-formylpyridine thiosemicarbazones have been reported [157], but no solids... 

The S-methyldithiocarbazates of both 2-formylquinoline, 18, and 1-formyliso-quinoline, 19, yield diamagnetic green [FeL2] complexes from iron(II) sulfate [131]. Coordination for both complexes is via the ring nitrogen, azomethine nitrogen and thiol sulfur based on infrared studies. 

Both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, form six coordinate [FeL2A2] complexes (A = Cl, Br) [156], The complexes formed with 26 are low spin, but complexes of 27 are high spin. For both ligands the bidentate coordination is via the azomethine nitrogen... 

Cu(3a)2] (BF4)2, [Cu(3a-H)Cl], and [Cu(3a)Br2], where 3a is 2-acetylpyridine N-methylthiosemicarbazone, have been prepared and studied spectroscopically [179], The former complex involves planar bonding by pyridyl and azomethine nitrogen atoms of each ligand and likely involves axial coordination of the thione sulfur atoms since v(d-d) = 15 670 cm , which is at lower energy... 

Copper(II) complexes of 2,6-lutidylphenylketone thiosemicarbazone, 38, have been prepared from copper(II) chloride and copper(II) bromide [186]. Similar to 2-pyridyl thiosemicarbazones, 38-H coordinates via the ring nitrogen, the azomethine nitrogen and the thiol sulfur based on infrared spectral assignments. Magnetic susceptibilities and electron spin resonance spectra indicate dimeric complexes and both are formulated as [Cu(38-H)A]2 with bridging sulfur atoms. The electronic spectra of both halide complexes show band maxima at 14500-14200 cm with shoulders at 12100 cm S which is consistent with a square pyramidal stereochemistry for a dimeric copper(II) center. 

Copper(II) complexes have been prepared with the 2-acetylpyridine N-oxide 3-azabicyclo[3.2.2.]nonylthiosemicarbazone, 25, and bonding occurs via the pyridine N-oxide oxygen, azomethine nitrogen and thiol sulfur [128]. Based on electronic and ESR spectra, bonding to copper(II) of uninegative, tridentate 25-H is considerably weaker than the related 2-acetylpyridine thiosemicarbazone, 4-H. The other copper(II) complexes reported to date have been prepared... 

Copperfll) complexes of 4,5-dimethyl-3-formylpyrazole IV-phenyl-thiosemicarbazone, 41, have been prepared by refluxing in ethanol [191]. [Cu(41-H)A], where A = Cl, Br, NO3, NCS and N3, were shown to involve bonding by Al(ring), azomethine nitrogen, and thiol sulfur atoms and all have magnetic moments in the range 1.8-1.9 B.M. The electronic and ESR spectral data for these complexes are comparable to that found for 2-acetylpyridine " iV-phenylthiosemicarbazone, 14 [181],... 

The S-methyldithiocarbazates of both 2-formylquinoline, 18, and 1-formyliso-quinoline, 19, when mixed with cobalt(II) salts in ethanol-dimethoxypropane, yield [Co(L-H)2]N03 and [Co(L-H)2]2[CoA4], where A = Cl, Br, I, NCS, or NCSe [145]. Magnetic and spectral data support these stoichiometries and bonding is via the ring nitrogen, azomethine nitrogen, and thiol sulfur. More recently [146], [Co(19-H)2]2[CoCl4] has been shown to have d-d bands consistent with the presence of both cobalt centers. 

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. 

C1 /C3 bond of the cyclopropenone initiated by attack of the azomethine nitrogen... 

Oxovanadium(IV) complexes with SBs (182 n = 1, 2, 4) were prepared and formulated as [(V0)2(SB)(H20)21 having coordinating sites at the azomethine nitrogen and enolic and phenolic O atoms. 5 values are in the range 1.62-1.70 BM, close to the spin-only value, but Xm measurements as a function of temperature were not performed. 

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