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-H(3)tpat) with essentially resonative structure and two copper(II)-based one-dimensional coordination chain structures, [Cu3Cl5(o-H(2)tpat)(H2O)]center dot MeOH center dot CH2Cl2 (1) and [Cu-2(o-H(2)tpat)(H2O)(MeOH)(NO3)(2)](NO3)center dot 3MeOH (2), with different structural patterns have been synthesized and characterized using single crystal X-ray diffraction analysis. For o-H(3)tpat, two crystalline forms showing different solid-state structural features are obtained from MeOH/Et2O (form I) and CH2Cl2/Et2O (form II), respectively. The o-H(3)tpat form I adopts an asymmetric-configured all amino resonative tautomer with three cis-trans-trans-arranged pyridyl groups, whereas the o-H(3)tpat 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-H(2)tpat(-), 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-H(3)tpat 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)(4)Cl-6} and two magnetically isolated {Cu(II)Cl-2} subunits. Antiferromagnetic interactions are found for the Cu-4 subunits (g = 2.33, 2J(1) = -5.6 cm(-1), 2J(2) = -8.6 cm(-1), 2J(3) = -4.1 cm(-1), and J(4) held to zero). For 2, it is considered as an infinite chain that composes of Cu-2 units antiferromagnetically coupled (g = 2.03, 2J(1) = -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-H(2)tpat(-) ligands.