Synthesis, Crystal Structures, and Magnetic Properties of Cyanide-Bridged Fe(III)−Mn(III) Complexes Based on Manganese(III)-Porphyrin and Pyridinecarboxamide Dicyanideiron(III) Building Blocks

A series of cyanide-bridged heterometallic manganese(III)-porphyrin complexes including two trinuclear sandwich-type FeIII−MnIII−FeIII compounds, three binuclear FeIII−MnIII compounds, and one ionic pair compound were designed and synthesized using five manganese(III)-porphyrin compounds and two pyridinecarboxamide dicyanideiron building blocks. Their crystal structures and magnetic properties have been systematically and comparatively investigated. X-ray diffraction analysis reveals the similar molecular structure among the two trinuclear and three binuclear cyanide-bridged complexes, respectively. In the trinuclear compounds 1 and 2 containing tetra(phenyl)porphyrin ligand, two dicyanide-containing units [Fe(bpb)(CN)2]− or [Fe(bpmb)(CN)2]− as monodentate ligands coordinate with the central Mn(III) atom of [Mn(TPP)(CH3OH)2]+ through one of their two trans cyanide groups to form the complex anion of {[Fe(bpb)(CN)2]2Mn(TPP)]}− or {[Fe(bpmb)(CN)2]2Mn(TPP)]}−, which further constructs the neutral complexes {[Fe(L)2]2[Mn(TPP)]}[Mn(TPP)(CH3OH)2]·xH2O·yCH3OH [L = bpb2− (1); L = bpmb2− (2)] with the help of one [Mn(TPP)(CH3OH)2]+ unit as a balanced cation. In the three binuclear FeIII−MnIII complexes containing a tetra(aryl)porphyrin ligand with increased bulky meso-attached aryl substituents, namely, {[Fe(bpb)(CN)2][Mn(TNPP)(H2O)]}·3H2O (3), {[Fe(bpb)(CN)2][Mn(TClPP)(CH3OH)]}·3CH3OH (4), and {[Fe(bpb)(CN)2][Mn(TMeOPP)(CH3CH2OH]}·2CH3OH·CH3CH2OH·H2O (5), two metal centers are bridged by one cyanide group of [Fe(bpb)(CN)2]−. In addition, the ionic compound [Fe(bpb)(CN)2][Mn(TDMeAPP)(CH3OH)2]·2H2O (6) was obtained by using [Fe(bpb)(CN)2]− and [Mn(TDMeAPP)(CH3OH)2]− as assembling segments. Investigation over magnetic properties of these heterometallic complexes reveals the ferromagnetic interaction between MnIII and FeIII magnetic centers for two trinuclear FeIII2MnIII and three binuclear FeIIIMnIII complexes with JMnFe = 3.28(1) and 2.47(2) cm−1 for 1 and 2, and JMnFe = 4.91(3), 2.55(3), and 1.72(1) cm−1 for 3, 4, and 5 on the basis of the Hamiltonian Ĥ = −2JŜMn(ŜFe(1) + ŜFe(2)) or Ĥ = −2JŜFeŜMn, respectively. Ac magnetic susceptibility measurements on two representatives 1 and 3 manifest their obvious frequency-dependent out-of-phase χm′′ signals below 3.5 K, along with clear frequency-dependent in-phase χm′ signals.