Phthalocyanines tridentate

As far as dyes are concerned, chelates of type Cb are termed 1 2 or symmetrical 1 2 metal complexes if the two tridentate ligands are equal, and mixed or unsymmetrical 1 2 metal complexes in the other case. Chelates of type Bb represent 1 1 metal complexes. The types Cb and Bb include, in general, azo and azo-methine metal complex dyes, whereas chelates of the quadridentate types Ac and Be are derived predominantly from formazan and phthalocyanine chromophores. 

Relatively few complexes of N-donor ligands are known. One of the best characterized is with the tridentate ligand terpyridyl, which reacts with scandium nitrate to form Sc(terpy )(N03 )s here scandium is connected to 9 atoms, but one Sc-O bond is considerably longer than the others, so a coordination number of 8.5 has been assigned. A range of porphyrin and phthalocyanine complexes exist syntheses often involve the high-temperature routes typical of the transition metals but recently a high-yield low-temperature route has been utilized to make octaethylporphyrin (OEP) complexes ... 

---