Synthesis, Structure, and Magnetism of a 1D Compound Engineered from a Biradical [5,5‘-Bis(3‘ ‘-oxide-1‘ ‘-oxyl-4‘ ‘,4‘ ‘,5‘ ‘,5‘ ‘-tetramethylimidazolin-2‘ ‘-yl)-2,2‘-bipyridine] and Mn^II(hfac)₂

The synthesis, crystal structure, and magnetic properties of a one-dimensional compound, {[Mn(hfac)2]2(biradical)}n (1), resulting from the coordination of bis(hexafluoroacethylacetonato)manganese(II) [Mn(hfac)2] with a biradical obtained by grafting two nitronyl nitroxide radicals in the 5 and 5‘ positions of a 2,2‘-bipyridine ligand are described. Compound 1 crystallizes in the triclinic P1̄ space group with the following parameters: a = 11.905(2) Å, b = 12.911(2) Å, c = 20.163(3) Å, α = 73.556(3)°, β = 80.850(3)°, γ = 82.126(3)°, Z = 2. The bipyridyl moiety acts as a chelate toward one [Mn(hfac)2] unit, while the pendent nitronyl nitroxide radicals are symmetrically bound in trans-configuration to additional [Mn(hfac)2] units. The result is infinite chains running along the c axis direction with the biradical bridging [Mn(hfac)2] units with pending bipyridine/Mn(hfac)2 cores. The magnetic behavior is characteristic of ferrimagnetic chains. Qualitatively we observe first the antiferromagnetic coupling (J2) of each manganese(II) center with two nitronyl nitroxide moieties, leading to a minimum in the χT product of 6.63 emu K mol-1 observed at 70 K and corresponding to a ground spin state S = 3/2 plus one extra spin S = 5/2 coming from the pending manganese(II) center. The increase of χT at lower temperature is understood as a fictive ferromagnetic coupling related to the true antiferromagnetic coupling J1 of the pseudospin S = 3/2 with spin S = 5/2 of the pending manganese(II). Along this approach (H = −JSiSj) the best fit (300−8 K) of the experimental data leads to J1 = −0.622 ± 0.022 cm-1 and J2 = −203 ± 3 cm-1 with g(Rad) = 2.0017 ± 0.0015 and g(Mn) = 2.0017 ± 0.0015.