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/kB = 26.7 K between the aminoxyl and the Ni(II) through the pyridine ring. Similarly, the thermal profile of χmol 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 χmolT (12.7 cm3 K mol−1 at 7 K).
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