Four Nitrogen Atoms

Synthesis of tetrazoles from aliphatic diazo compounds 85MI5 Tetrazolium salts 90KGS1587. 

The cyclic tetramine NH(CH2)3NH(CH2)2 2 gives a mixture of products when it reacts with P(NMc2)3, in which the phosphorane tautomer (40) predominates, in contrast to the P tautomers which arise from the isomer -fNH(CH2)3[NH(CH2)2]2NH(CH2)3.  

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The only known example under such heading is that incorporating four nitrogen atoms, the tetrazoloquinoline. Although they can exist in two annulated ring systems, only examples of one of them, l,2,3,4-tetrazolo[l,5-ajquinolines are reported (Fig. 11). 

How many electrons does each of the four nitrogen atoms in purine contribute to the aromatic w system ... 

Structure of heme. In the hemoglobin molecule, the Fe2+ ion is at the center of an octehedron, surrounded by four nitrogen atoms, a globin molecule, and a water molecule. 

Heme, an essentially planar, slightly puckered, cyclic tetrapyrrole, has a central Fcj" linked to all four nitrogen atoms of the heme, to histidine F8, and, in oxyMb and oxyHb, also to O2. 

Another illustrative example is that of the Co(II) ion in vitamin B12 (cyanocoba-lamin) given in Figure 5.6. The cobalt is coordinated by four nitrogen atoms from... 

This structure shows the four nitrogen atoms that provide the electron pairs for forming bonds to metals. The chlorophylls consist of several members of a series, three of which are chlorophyll a, c, and d, which have structures derived from a molecule known as chlorin that is shown in Figure 22.17. 

FIGURE 22.20 The structure of heme. Note that the Fe resides above the plane of the four nitrogen atoms. 

When an oxygen molecule is attached to the iron in the heme structure, the Fe2+ changes from high spin to low spin, but the iron remains in the +2 oxidation state. In the heme structure, the Fe2+ ion resides above the plane of the four nitrogen atoms in the porphyrin structure, and an imidazole group is attached to the iron on the side away from the plane of the four nitrogen atoms. This structure is shown in Figure 22.20. 

Stotter, 1979) in which single pendant arms incorporate functional groups such as -CH2CONH2 and -CH2CH2CH2NH2. The metal derivatives of these systems show a superficial resemblance to particular biochemical systems such as haemoglobin, in which the metal ion is surrounded by four nitrogen atoms in a square-planar fashion with a fifth donor, attached to another part of the molecule, occupying an axial coordination site. 

TPMA ligand typically coordinates to the copper center in a tetradentate fashion, similarly to Me6TREN [117]. However, the role of counterion coordination (in particular Br and Cl ) in these complexes still remains very unclear. Recently, we were able to isolate and structurally characterize neutral CuI(TPMA)Cl [118] and CuI(TPMA)Br [119] complexes. To our surprise, both complexes were pseudopenta-coordinated (Fig. 6). In CuI(TPMA)Cl, the copper ion was coordinated by four nitrogen atoms with bond lengths of 2.0704(11), 2.0833(11), 2.0888(11) A for the equatorial Cu-N, and 2.4366(11) A for the axial Cu-N bonds, and a chlorine atom with a bond length of 2.3976(4) A. The molecular structure of Cu (TPMA)Br was similar to the structure of Cu (TPMA)Cl and the complex was also found to be pseudopentacoordinated in the solid state due to the coordination of TPMA (Cu-N... 

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