Novel metal-linked face-to-face porphyrazine dimer

We report the synthesis and physical studies of a novel porphyrazine (pz) dimer {1[Ni,Cu]}₂, which has Ni(II) ions incorporated into the pz cores and is linked by two Cu(II) ions coordinated to bis(picolinamide) chelates attached to the pz periphery. {1[Ni,Cu]}₂ was prepared from precursor pz 2 with a selenodiazole ring fused to the pz core. This ring was deprotected to form the diamino-pz 3, which reacted with 2 mol of picolinoyl chloride hydrochloride to form pz 1[2H,2H], with peripheral bis(picolinamide) chelates; this was metalated to form {1[Ni,Cu]}₂. The crystal structures of 1[2H,2H] and {1[Ni,Cu]}₂ are presented. The latter is a dimer in which parallel, face-to-face pz's with an average separation of 3.30 Å are linked through the peripheral picolinamide ligands by a pair of peripheral Cu(II) ions. Each Cu(II) is coordinated with distorted square-planar geometry by a picolinamide from each pz. In this report, we focus on the interaction of these two peripheral Cu(II) ions. We discuss the preparation and magnetic properties of the pz dimer complex {1[Ni,Cu]}₂ with two Cu(II) ions in the peripheral chelate but a diamagnetic metal ion Ni(II) in the pz core. Although {1[Ni,Cu]}₂ contains two Cu(II) ions (S = 1/2), we could detect no electron paramagnetic resonance signal, which suggests very strong antiferromagnetic exchange between those two Cu(II) ions. Temperature-dependent magnetic susceptibility measurement gives an exchange splitting between the S = 0 ground state and the excited triplet state of Δ = 660 cm^-1.