Synthesis and magnetic properties of 2,2-diphenyl-1,2-dihydroquinoline N-oxyl carrying an ethynyl group at the 5-position

Abstract

Two aromatic nitroxyl radical derivatives of 2,2-diphenyl-1,2-dihydroquinoline N-oxyl (1), namely, 5-[2-(trimethylsilyl)ethynyl]-2,2-diphenyl-1,2-dihydroquinoline N-oxyl (2) and 5-ethynyl-2,2-diphenyl-1,2-dihydroquinoline N-oxyl (3), were synthesized, and their magneto-structural correlation was described in connection with their assembled structures. Single-crystal XRD analysis of 3 revealed a hydrogen bond between the oxygen atom in the nitroxyl group and the terminal hydrogen atom of the ethynyl group with d_O⋯(H)C = 3.099(5) Å. SQUID measurements revealed that 3 follows a 1D antiferromagnetic chain model with J = −10.4 cm⁻¹. In contrast, a slight increase in the χ_MT value to 0.44 emu K mol⁻¹ was observed in 2, with a decreasing temperature indicating the presence of a weak intermolecular ferromagnetic interaction. These magnetic behaviors differ from that of the unsubstituted radical 1.