A New Quinoxalinyl-Substituted Nitronyl Nitroxide Radical and its Five-Spin CuII and Four-Spin MnII Complexes: Syntheses, Crystal Structures, and Magnetic Properties

Abstract

A new radical of QNXL-2NIT (1) (QNXL-2NIT = 2-(2-quinoxalinyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) and its complexes [Cu(hfac)2]3(QNXL-2NIT)2·2CHCl3 (2) and [Mn(hfac)2]2(QNXL-2NIT)2 (3) (hfac = 1,1,1,5,5,5-hexfluoroacetylacetone) were first reasonably designed and synthesised in this paper. The X-ray structure determination revealed that by introducing the quinoxalinyl ring group to the nitronyl nitroxide radical, QNXL-2NIT affords more coordination sites for metal ions. We successfully obtained its copper complex with linear tri-nuclear five-spin structure. However, when we substituted MnII as the central metal, complex 3 exhibits a rectangle-like four-spin framework containing two MnII ions and two radicals in one molecule. The magnetic study of the two complexes shows that there are strong antiferromagnetic interactions between the radical and the terminal CuII ions with g = 2.25, J = –291.67 cm–1 and zJ′ = –0.25 cm–1 and the dominating interactions between the MnII ion and the radical in complex 3 are also antiferromagnetic with the parameters of g = 1.99, J 1 = –77.00 cm–1 and J 2 = 0.34 cm–1.