Synthesis of a series of hetero-multi-spin Ln2Cu3 complexes based on a methyl-pyrazole nitronyl nitroxide radical with slow magnetic relaxation behaviors

Abstract

Multinuclear hetero-tri-spin complexes based on a methyl-pyrazole nitronyl nitroxide radical, namely, [Ln₂Cu₃(hfac)₁₂(4-NIT-MePyz)₄] (Ln = Gd(1), Tb(2), Dy(3); hfac = hexafluoroacetylacetone; 4-NIT-MePyz = 2-{4-(1-methyl)-pyrazolyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been successfully obtained through a one-pot reaction of the radical ligand (4-NIT-MePyz) with Cu(hfac)₂ and Ln(hfac)₃. These 2p–3d–4f complexes exhibit five-nuclear structures with the sequence [Cu–Rad–Ln–Rad–Cu–Rad–Ln–Rad–Cu], in which each 4-NIT-MePyz radical acting as a bidentate bridging ligand is coordinated to one Ln(hfac)₃ unit through one oxygen atom of the NO groups and to one Cu(hfac)₂ unit with one nitrogen atom from the pyrazole ring. For complex 1, based on the spin Hamiltonian calculations and MAGPACK program, it is concluded that there exist ferromagnetic couplings between Gd^III and NIT radicals, as well as between Cu^II and free radicals with J₁ = 6.8(1) and J₃ = 1.3(2) cm⁻¹, respectively, and antiferromagnetic interactions between radical and radical with J₂ = −2.8(5) cm⁻¹. Complex 2 shows frequency-dependent out-of-phase signals under a zero or 2000 Oe dc field indicating single-molecule magnetic behavior.