Tetraaza macrocyclic complexes of Cu(II), Co(III) and Ni(II) derived from template condensation of 2,6-pyridinedicarbohydrazide and 2,6-diacetyl-pyridine: Stability investigation and coloring properties on plastics

Completely conjugated 14-membered ring hexaaza ligand complexes of Cu(II), Co(III) and Ni(II) were synthesized by the template cyclo-condensation reaction of 2,6-diacetylpyridine and 2,6-pyridinedicarbohydrazide: [Cu (HL)Cl]center dot 1.35H2O (1), [Cu(HL)Br]center dot CH3OH (2), [Cu(L)(H2O)]center dot 4H2O (3), [Co(HL)Cl2]center dot CH3OH (4), (H3O)[Co(H2L) Cl2][Co(HL)Cl2]Cl2 center dot H2O (5), [Co(HL)(SCN)2]center dot CH3OH (6), [Ni(L)]center dot 3H2O (7) and (H3O)[Ni(L)]Cl center dot H2O (8). The structure of all complexes derived from this novel diprotic macrocyclic ligand H2L (5,7-dimethyl-3,4,8,9-tetraaza-1,6(2,6)-dipyridinacyclodecaphane-4,7-diene-2,10-dione) were determined by single crystal X-ray diffraction method. The tetraaza 14-membered conjugated macrocycle is N4-tetracoordinated to metal, adopts an essentially planar configuration and forms four fused metallocycles rings, two five-membered and two sixmembered chelates. The structures of the studied complexes reveal three isomers out of three possible: with a 5-6-5-6 order of alternation of metallocycles for 1-6, the 5-5-6-6 isomer in 8 and the coexistence of two different isomers with 5-5-6-6 and 6-6-5-5 alternation of metallocycles in 7. Based on the protonation state of the macrocyclic ligand, four forms of the ligand have been registered: bis-deprotonated L2- (compounds 3, 7 and 8), monodeprotonated HL- (1, 2 and 4), neutral H2L (5) and for compound 6 tautomeric (amide -> imidic acid) HLform. The organisation of crystal structures 1-8 depends on the nature of the metal and the composition of the solvents and outer-sphere ions, but shows clear common features for the same type of metal. The hydrolytic study demonstrated a high stability of the Co(III) and Ni(II) complexes in acidic solutions and the most thermally stable are the complexes 3 and 7 with the limit of 350 degrees C for Ni(II) complex. Testing of the coloring properties of the [Ni (L)] (8) complex on plastics indicates a high coloring efficiency, especially for polyamide polymers.