Unexpected linkage isomerism in chiral tetranuclear bis-tridentate (1,2,3-triazol-4-yl)-picolinamide (tzpa) grids

Abstract

The synthesis of a chiral bis-tridentate (1,2,3-triazol-4-yl)-picolinamide (tzpa) ligand is described and its coordination chemistry with Cu(NO₃)₂ and [Cu(MeCN)₄]PF₆ is explored in the crystalline phase as well as in solution. Chiral [2 × 2] tetranuclear square grid complexes [Cu₄(H₂1)₄](NO₃)₈ and [Cu₄(H1)₄](PF₆)₄ were observed, and crystallographically analysed, these being linkage isomers with N₄O₂ and N₅O coordination spheres, respectively. These come about by an unusual in situ amide deprotonation and coordination, which accompanies a Cu^I → Cu^II oxidation process.