Synthesis and properties of dimetallic M¹[Pz]-M ²[Schiff base] complexes

We report the synthesis and physical characterization of a series of peripherally functionalized porphyrazines (pz's) 1[M¹; M ²; R], where M¹ is a metal ion incorporated into the pz core, M² is a metal ion bound to a bis(5-tert-butyl-salicylidenimine) chelate built onto two amino nitrogen attached to the pz periphery, and R is a solubilizing group (either n-propyl (Pr) or 3,4,5-trimethoxyphenyl (TMP) group) attached to the remaining carbons of the pz periphery. The 1[M¹; M²; R] species are prepared from precursor pz's with a selenodiazole ring; they are deprotected to form the diamino pz, which reacts with two moles of 5-tert-butyl-2-hydroxybenzaldehyde to form the Schiff base pz. This is metalated to form 1[M¹; M²; R]. The crystal structures of 1[2H; Ni; Pr] and 1[Cu; ClMn; Pr] are presented. The EPR spectra of the M ¹-M² "isomers" prepared with Cu(II) (S = 1/2) and ClMn(III) (S = 2) ions, 1[ClMn; Cu; Pr] and 1[Cu; ClMn; TMP], are a superposition of spectra expected for the S = 3/2 and S = 5/2 total-spin manifolds that result from strong Heisenberg coupling between the partner spins. The exchange splitting between the two manifolds, as determined by temperature-dependent magnetic susceptibility measurements, is equivalent for the two M¹-M² "isomers", Δ/k_B ≈ 20-25 K, which suggests a σ-pathway for exchange coupling.