Porphyrazines Peripherally Functionalized with Hybrid Ligands as Molecular Scaffolds for Bimetallic Metal-Ion Coordination

We report the synthesis and physical characterization of a new family of peripherally functionalized porphyrazine
(pz) compounds, denoted 1[M1, M2], where metal ion M1 is incorporated into the pz core and metal ion M2 is bound
to a salicylidene/picolinamide “hybrid” chelate built onto two nitrogen atoms attached to the pz periphery. The
complexes 1[MnCl, Cu], 1[VO, Cu], and 1[Cu, Cu] have been prepared, and crystal structures show 1[MnCl, Cu]
and 1[VO, Cu] to be isostructural. These complexes have been subjected to electron paramagnetic resonance and
temperature-dependent magnetic susceptibility measurements. The variation of the ligand-mediated exchange splittings
(Δ) in these complexes is striking:  Δ/kB values for 1[MnCl, Cu] and 1[VO, Cu] are 22 and 40 K, respectively, while
Δ/kB for 1[Cu, Cu] is only 1 K. These coupling results are explained in terms of the relative orientation of the M1
and M2 orbitals and reflect the fact that the ligand set of M2 in the periphery is rotated in-plane by 45° relative to
the effectively coplanar pz ligand set of M1. The exchange couplings are essentially the same as those we determined
for the Schiff base porphyrazines (pzs). Thus, the hybrid ligand has eliminated the dimerization found to occur
when Cu(II) is bound to the periphery of bis(picolinamido) pzs and has created a more robust ligand system than
the Schiff base pzs while retaining the ability they show to promote spin coupling between M1 and M2.