Diazopyridine-Ni(ii) complexes exhibiting intra-chain ferromagnetic interaction after irradiation: formation of magnetic gel

Diazopyridine-nickel complexes, 1 and 2, were obtained by mixing di(4-pyridyl)diazomethane, D1py₂, with Ni(R-hfpip)₂; hfpip = 4-(4-R-phenylimino)-1,1,1,5,5,5-hexafluoro-2-pentanone and R = n-hexyl (1) and n-octyl (2), in a 1 : 1 ratio. The discrete reference complex [Ni(n-hexyl-hfpip)(4NOpy)₂] (3) was also prepared. In the tube inversion test and the rheological measurements, the sample (20 mM) of 1 and 2 dissolved in EtOH-20% CH₂Cl₂ solution showed gelation behavior at -4 °C. In a scanning transmission electron microscopy (STEM) image of the xerogel sample, fibers with widths of 500-700 nm were observed. The Vis-NIR spectrum of the gel sample for 1 showed the typical broad absorption at ∼995 nm due to the octahedral Ni(ii) complex, suggesting that the pyridine ligands in D1py₂ coordinated to the Ni(ii) ion to form the chain structure. Complex 3 showed ferromagnetic interaction with J/k_B = 26.7 K between the aminoxyl and the Ni(ii) through the pyridine ring. Similarly, the thermal profile of χ_mol values after irradiation of the gel sample of 1 showed a ferromagnetic interaction between the generated triplet carbenes and the Ni(ii) ions and provided a magnetic chain structure. The magnetic correlation length was estimated to be 4-5 units from the maximum value of χ_molT (12.7 cm³ K mol^-1 at 7 K).