Infinite Copper(II) Coordination Architectures from a Resonative Aminotriazine-Derived Tripodal Ligand: Synthesis, Structures, and Magnetic Properties

The ligand 2,4,6-tris­(2-picolylamino)-1,3,5-triazine (o-H3tpat) with essentially resonative structure and two copper­(II)-based one-dimensional coordination chain structures, [Cu3Cl5(o-H2tpat)­(H2O)]·MeOH·CH2Cl2 (1) and [Cu2(o-H2tpat)­(H2O)­(MeOH)­(NO3)2]­(NO3)·3MeOH (2), with different structural patterns have been synthesized and characterized using single crystal X-ray diffraction analysis. For o-H3tpat, two crystalline forms showing different solid-state structural features are obtained from MeOH/Et2O (form I) and CH2Cl2/Et2O (form II), respectively. The o-H3tpat form I adopts an asymmetric-configured all-amino resonative tautomer with three cis–trans–trans-arranged pyridyl groups, whereas the o-H3tpat form II adopts also an identical resonative structure but where two of the three pyridyl groups are in a cis-manner and the third one is nearly coplanar with the central aminotriazine core. On the other hand, the designed tripodal ligand in both Cu­(II)-complexes serves as a monoanion, o-H2tpat–, which suits a propeller-configured all-imino resonative structure in 1 and a syn–anti-configured amino–imino–imino resonative structure in 2. These observations significantly indicate that the o-H3tpat ligand can self-adjust and interconvert its conformation via a possible structure transformation associated with proton-shift to adapt a change in the crystallization and self-assembly reaction systems. In the magnetic point of view, 1 is treated as repeated chains composed of infinite {Cu6Cl10} units wherein the hexanuclear unit is further decomposed to one {Cu­(II)4Cl6} and two magnetically isolated {Cu­(II)­Cl2} subunits. Antiferromagnetic interactions are found for the Cu4 subunits (g = 2.33, 2J1 = −5.6 cm–1, 2J2 = −8.6 cm–1, 2J3 = −4.1 cm–1, and J4 held to zero). For 2, it is considered as an infinite chain that composes of Cu2 units antiferromagnetically coupled (g = 2.03, 2J1 = −0.2 cm–1). The small antiferromagnetic exchange constants in both 1 and 2 suggest that the unpaired spins do not effectively interact through the tripodal o-H2tpat– ligands.