Heisenberg Spin Chains via Chalcogen Bonding: Noncovalent S•••O Contacts Enable Long-Range Magnetic Order

The new radical ligand 5,8-dimethyl-1,4-dioxonaphtho[2,3-d][1,2,3]dithiazolyl (1) is reported. Two crystal polymorphs, 1 alpha and 1 beta, differing in their pancake-bonded dimerization motif and S center dot center dot center dot O contact network, are identified. The self-assembly of Mn(II) metal ions with 1 leads to the formation of [Mn(hfac)(2)](3)(1)(2) that exhibits a Mn(II)-radical-Mn(II)-radical-Mn(II) linear arrangement of three Mn(hfac)2 units bridged by two radical ligands (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). Characterization by single-crystal X-ray diffraction of this Mn(II) complex packing structure reveals close noncovalent S center dot center dot center dot center dot O contacts between the [Mn(hfac)2]3(1)2 units in one dimension along the b-c direction. The magnetic properties of the coordination complex are characterized by dc and ac susceptibility measurements on a microcrystalline solid. The magnetic data down to 4.8 K indicate the presence of effective ferromagnetic interactions (J/k(B) = +0.16 K) between the molecular S-T = 13/2 units along the supramolecular chain involving noncovalent S center dot center dot center dot O contacts. Below 2.9 K, a non-zero out-of-phase component appears in the ac susceptibility, indicating the presence of a three-dimensional magnetic phase transition.

Automated summary

A new radical ligand has been reported, with two crystal polymorphs identified. The self-assembly of Mn(II) metal ions with the ligand leads to a linear arrangement of three Mn(II) units bridged by two radical ligands. Magnetic measurements indicate effective ferromagnetic interactions along the supramolecular chain involving noncovalent S center dot center dot center dot O contacts.