Work

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

Year: 2024

Type: article

Abstract: 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]·1.35H 2 O ( 1 ), [Cu(HL)Br]·CH 3 OH ( 2 ), [Cu(L)(H 2 O)]·4H 2 O ( 3 ), [Co(HL)Cl 2 ]·CH 3 OH ( 4 ), (H 3 O)[Co(H 2 L)Cl 2 ][Co(HL)Cl 2 ]Cl 2 ·H 2 O ( 5 ), [Co(HL)(SCN) 2 ]·CH 3 OH ( 6 ) , [Ni(L)]·3H 2 O ( 7) and (H 3 O)[Ni(L)]Cl·H 2 O ( 8 ). The structure of all complexes derived from this novel diprotic macrocyclic ligand H 2 L (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 N 4 -tetracoordinated to metal, adopts an essentially planar configuration and forms four fused metallocycles rings, two five-membered and two six-membered 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 L 2− (compounds 3, 7 and 8 ), monodeprotonated HL − ( 1, 2 and 4 ), neutral H 2 L ( 5 ) and for compound 6 tautomeric (amide → imidic acid) HL − form. 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 °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.

Source: Journal of Molecular Structure

DOI: 10.1016/j.molstruc.2024.140021

Authors: Vasile Lozovan, Victor Ch. Kravtsov, Ion Bulhac, Oleg Petuhov, Titus Vlase, Polina N. Bourosh