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.