1,10-Phenanthroline-5,6-dione-bridged FeCo complexes: a DFT investigation of the electronic lability

Heterometallic FeCo dinuclear complexes on the basis of the redox-active 1,10-phenanthroline-5,6-dione with ancillary bis(pyrazolyl)borate anions and tetradentate N-donor ligands (N,N′-dialkyl-2,11-diaza[3.3]-(2,6)pyridinophane and tris(2-pyridilmethyl)amine derivatives) were studied by the DFT UTPSSh/6–311 + + G(d,p) method in a view to possible spin-crossover (SCO) or valence tautomeric (VT) interconversions. The electronic structures (namely, spin and oxidation states of the electronically labile centers) and magnetic properties of the considered compounds were found to be determined by the position of the outer-sphere PF 6 – counterion and the type of N-donor base. The most energetically preferred isomers contain a counterion near the cobalt ion. The presence of PF 6 – next to the iron center stabilizes the ferric state of this metal and the dianionic form of the 1,10-phenanthroline-5,6-dione linker ligand. The variation of the structural peculiarities allowed us revealing the dinuclear complexes prone to exhibit the SCO and VT processes, which makes them promising building blocks of magnetic materials.