Nickel-macrocycle complex square pyramidal

The properties of nickel(II) complexes with unsaturated macrocycles which contain pyridyl groups are included in a very comprehensive review article.2626 The complexes are usually square planar with the exceptions of the trans octahedral NiX2(CR)2743 (CR = 2,12-dimethyl-3,7,ll,17-tetraazabicyclo[11.3.1]heptadeca-l(17),2,ll,13,l5-pentaene) and of the diamagnetic square pyramidal NiBr(CR)]Br-H20 (381).2747 The diamagnetic complexes Ni(CR)(C104)2 give rise to square planar octahedral equilibria in coordinating solvents,2744,2746 whereas... 

The situation with pendant phenol groups is much less ambiguous. The crystal structure of the nickel(II) complex [Ni H 1[14]ane-N4C6H5OH]+ (Fig. 5) shows it to be a square-pyramidal, high-spin species and the reduction potential of the nickel(III) complex is 0.15 V lower than that of the parent saturated 14-membered macrocyclic complex (100). Strong coordination by phenolate oxygen is even more... 

The nickel ) complex of 92 cannot be prepared directly via the template method, but can be prepared by a transmetallation procedure. Synthesis of the macrocycle in the presence of one of the metal ions known to be effective as a template is followed by a metal exchange process in solution to insert the nickel ) ion. This cation exhibits a strong preference for the square planar, square pyramidal, and octahedral geometries 79). Thus the failure of the nickel ) cation to behave as a template ion in the synthesis of 92 is probably due to the disinclination of the metal to accommodate the pentagonal array of donor nitrogen atoms necessary for reaction to occur. 

The structures determined by X-ray analysis of the complexes [Ni(Me3[12]eneN3)2](NCS)2 (Me3[12]eneN3 = 2,4,4-trimethyl-l,5,9-triazacyclododec-l-ene) and [Ni(TRI)(H20)N03]N03 (TRI = tribenzo[6,/,)][l,5,9]triazacydododecane) show that the two triaza macrocycles coordinate facially in both square pyramidal and octahedral complexes. Other complexes with triaza macr cles have been prepared and are assumed to be either five- or six-coordinate.Selected examples of nickel(II) complexes with unsaturated macrocycles are reported in Table 106. 

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