Versatile coordination behaviour of the chloro-tetrazine-picolylamine ligand: mixed-valence binuclear Cu()/Cu() complexes

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 48; no. 31; pp. 11966 - 11977
• Main Authors: Stetsiuk, Oleh, Petrusenko, Svitlana R, Sorace, Lorenzo, Lupan, Alexandru, Attia, Amr A. A, Kokozay, Vladimir N, El-Ghayoury, Abdelkrim, Avarvari, Narcis
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 06.08.2019
• Subjects: Bimetals; Chemical Sciences; Coordination; Coordination chemistry; Copper; Crystallography; Ligands; Precursors
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt02379h

The 3-Cl-6-amino-(2′-picolyl)-1,2,4,5-tetrazine ligand HL 1 has been synthesized and structurally characterized. Its versatile coordination behavior has been evidenced through reactions with Cu(Hfac) 2 and Cu(triflate) 2 precursors, which provided mixed-valence bimetallic Cu 1.5 Cu 1.5 complexes [Cu 2 (μ-Cl)( L 1 ) 2 ] 2 and [Cu 2 (μ-triflate)( L 1 ) 2 ] 5 . Changing the Cu( ii ) precursor and the solvent leads to the formation of mononuclear octahedral Cu( ii ) complexes [CuCl 2 ( HL 1 ) 2 ]·2CH 3 CN 3 and [Cu(Hfac) 2 ( HL 1 )] 4 , in which only the amino-pyridine unit is involved in the coordination of the metal center. In contrast, in complexes 2 and 5 , the ligands are deprotonated and bridge the metal centers as pyridine-amido-tetrazine fragments, while a bridging chloride or triflate ligand completes the coordination sphere of the metal ions. The Cu-Cu distances of 2.4313(4) Å in 2 and 2.5198(10) Å in 5 lie among the shorter values within mixed-valence bimetallic Cu complexes. Mixed-valence character is strongly supported by DFT calculations, showing the equal repartition of the unpaired electron between the two metal centers. Neutral mixed-valence binuclear Cu( i )/Cu( ii ) complexes, containing the deprotonated chloro-picolylamine-tetrazine ligand, have been prepared and characterized by single crystal X-ray diffraction and DFT calculations.