Four-coordinate nitrogen

In contrast, Ni[pz(iV-Me2)8] C60 (lOOd) has a totally different supramolecular structure featuring a noncentrosymmetric 1 1 complex with a strongly warped pz unit. The plane of diametrically opposite pyrrole rings is being rotated by -30° with respect to each other about their N—N vectors with the nickel and the four coordinated nitrogen atoms are coplanar to within 0.006 A. Each C60 unit lies within a cleft formed by two steeply inclined (by -12°) Ni-pz molecules (Fig. 33), the shortest Ni—C (C60) distances are 3.29 and 3.64 A. 

The distortion is the result of the strain imposed on the whole molecule by the geometric requirements of the corrole structure. It is not, however, very significant the rhodium atom is displaced by only 0.26 A from the plane of the four coordinating nitrogen atoms, a value much smaller than that observed in the structure of the P-unsubstituted complex Co(Corrole)PPh3 shown in Fig. 12 where the cobalt atom is displaced by 0.38 A from the macrocycle plane [32]. In both compounds the four coordinating nitrogen atoms are strictly coplanar. 

Distance from the mean plane of four coordinating nitrogens... 

The geometry observed apparently provides for a much more symmetrical distribution of bond lengths around the four-coordinate nitrogen atom (sp3 hybridized). In fact, the normal spinel, GeSi2N4, where the tetrahedral sites are... 

The structural chemistry and solution behavior of lithium diisopropylamide (LiN(CHMe2)2, EDA) typifies the complexities of these systems. Although the base-free compound crystallizes as infinite helical chains with two-coordinate lithium and four-coordinate nitrogen, it is isolated from A,A,A, A -tetramethylethylenediamine (TMEDA)/hexane mixtures as an infinite array of... 

All other iminoalanes known are self-assembled polycyclic cages, 55-57, containing four-coordinate aluminum and four-coordinate nitrogen, thus making full use of the s and p orbitals in bonding. 

Sulfur-Nitrogen Polymers Containing Four-Coordinate Sulfur(Vl)... 

Cytochromes. A cytochrome is a protein containing a heme with an iron cation bonded to four donor nitrogen atoms in a square planar array. Figure 20-29a shows the structure of cytochrome c, in which a histidine nitrogen atom and a cysteine sulfur atom occupy the fifth and sixth coordination sites of the octahedral iron center. 

The distance between the diagonal nitrogen atoms is approximately 4 A [ 12]. The distortion induced by the incorporated metal is negUgible and planar four-coordinated metallocomplexes are produced. Therefore, the metal-nitrogen dis-... 

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