N donor macrocycles

The preferential coordination geometry of the template metal ion determines the nature of the macrocycle that is formed, e.g., Ni2 + and Cu2+ are particularly effective template ions for the synthesis of N-donor macrocycles containing 4 nitrogen atoms that can be arranged in a plane and, hence, form a square planar macrocycle-metal complex. 

Ni(II) ions, most commonly used in the synthesis of N-donor macrocycles, were found to be as effective as Mg(II) ions. 

There is a particularly extensive and rich coordination chemistry associated with iron(II) N donor macrocycles. The coordination chemistry of the biologically important iron porphyrin complexes has been of interest since the classic studies of Fischer, and over recent years there has been a resurgence of work on these and also on a wide range of related synthetic macrocyclic complexes. This section concentrates on their coordination chemistry, and where appropriate highlights enhanced ligand reactivity specifically induced by the iron(II) centre. First saturated ligands are discussed and then the unsaturated systems, with the particularly well-studied porphyrins and phthalocyanines being dealt with in separate subsections. 

Ni complexes are relatively rare and are often stabilized by specialized ligands such as N-donor macrocycles and P-donor tripodal systems. Ni has a d electron configmation and its complexes are therefore paramagnetic with one unpaired electron. They show a variety of stereochemistries depending upon the ligands present, although fom or five... 

The report by Curtis of the condensation of [Ni(en)3] + with acetone to give the open-chain condensation product and subsequently the macrocyclic complex (equation 8) was the first example of the synthesis of N-donor macrocycles by a metal template, and predates work on the oxycrown ligands such as 18-crown-6 ([18]ane06). 

The few data available on thiocyanates indicate N-coordination in the solid. The octacyanometaUate Nb(CN)8 has been used for supramolecular magnetic architectures by self assembly with ML + complexes (M = Ni , Mn , L = N-donor macrocycle). ... 

N-donor macrocyclic ligands, based on 1,4,7-trithiacyc-lononane and carrying three pendant arms bearing alkoxides give nonoxo vanadiumfTV) complexes. ... 

O-donor macrocycles can bind alkali, alkaline, and rare earth metals predominantly by electrostatic forces. By contrast, N-donor macrocycles can bind softer Lewis acids like transition metals, and in this particular case, the interactions are predominantly coordinate in nature. Thia-substituted ligands are much softer than O- and N-donor macrocycles and can selectively bind softer Lewis acids like Ag+ and Hg ". ... 

Poon and Mak have classified the reactivities of a range of macrocyclic ligand complexes of the type /ra 5-[Co(L)(X)(Y)]+ (L=quadridentate N-donor macrocycle X and Y unidentate anionic ligands with X the leaving group) into three categories as shown in Table 30. Those ions in classification I react with a rate-determining proton transfer and kon=ki reactions (30)—(32), and at... 

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