Kathryn E. Preuss

Fine-tuning the single-molecule magnet properties of a [Dy(III)-radical]2 pair.

A supramolecular species composed of a pair of nonequivalent Dy(III)-radical complexes exhibits single-molecule magnet (SMM) properties. The weak effective antiferromagnetic coupling between the Dy(III) ions can be compensated by application of a small (700 Oe) dc field, revealing the relaxation mode of the two distinct SMMs. These unique results illustrate how the dynamics of a supramolecular [Dy-Radical]2 SMM can be fine-tuned by the exchange-bias and an applied magnetic field.

Synthesis and magnetic properties of a 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl dimanganese complex.

A spin-bearing bis-bidentate ligand, designed from a pyrimidyl-substituted R-CN2S2 neutral radical, is used to co-ordinate two Mn(II) metal centres yielding a thermally stable complex with antiferromagnetic coupling between the ligand-centred spin and the metal-centred spins, and thus an overall ferrimagnetic coupling scheme with a ground state S = 9/2.

High-Spin Ribbons and Antiferromagnetic Ordering of a Mn II - Biradical-Mn II Complex

A binuclear metal coordination complex of the first thiazyl-based biradical ligand 1 is reported (1 = 4,6-bis(1,2,3,5-dithiadiazolyl)pyrimidine; hfac =1,1,1,5,5,5,-hexafluoroacetylacetonato-). The Mn(hfac)2-biradical-Mn(hfac)2 complex 2 is a rare example of a discrete, molecular species employing a neutral bridging biradical ligand. It is soluble in common organic solvents and can be easily sublimed as a crystalline solid. Complex 2 has a spin ground state of S(T) = 4 resulting from antiferromagnetic coupling between the S(birad) = 1 biradical bridging ligand and two S(Mn) = 5/2 Mn(II) ions. Electrostatic contacts between atoms with large spin density promote a ferromagnetic arrangement of the moments of neighboring complexes in ribbon-like arrays. Weak antiferromagnetic coupling between these high-spin ribbons stabilizes an ordered antiferromagnetic ground state below 4.5 K. This is an unusual example of magnetic ordering in a molecular metal-radical complex, wherein the electrostatic contacts that direct the crystal packing are also responsible for providing an efficient exchange coupling pathway between molecules.

Metal complexes of thiazyl radicals

A diverse variety of thiazyl radicals is known. Intense study of these heterocycles continues in the pursuit of molecule-based materials with novel, academically interesting, and technologically relevant properties. Coordination of these species to metal atoms and ions has focused primarily on the 1,2,3,5-dithiadiazolyl 2 and 1,3,2-dithiazolyl 6. The potential of these two heterocycles as ligand building-blocks has, by no means, been fully exploited. From the structural and electronic similarities between 2 and the verdazyl and nitronyl nitroxide radicals, it is apparent that similar radical ligand designs ought to be achievable. The sulfur atoms of 2 lend a unique feature to this radical that may yet be employed as a means of controlling intermolecular interactions or developing multi-metal species. The recent report of sulfur coordination to 6 demonstrates that there is yet more design flexibility available from this thiazyl as well. Coordination complexes of other radical thiazyls have begun appearing in the literature. This field is currently in its infancy and is starting to be recognized as an enormous source of untapped potential in the future development of molecule-based materials.

Trinuclear Mn(II) complex with paramagnetic bridging 1,2,3-dithiazolyl ligands

The first metal coordination complex of a radical ligand based on the 1,2,3-dithiazolyl heterocycle is reported. 6,7-Dimethyl-1,4-dioxo-naphtho[2,3-d][1,2,3]dithiazolyl acts as a bridging ligand in the volatile trinuclear Mn(hfac)(2)-Rad-Mn(hfac)(2)-Rad-Mn(hfac)(2) complex (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The Mn(II) and radical ligand spins are coupled anti-ferromagnetically (AF) resulting in an S(T) = 13/2 spin ground state.

A third polymorph of 4‐(2,6‐difluorophenyl)‐1,2,3,5‐dithiadiazolyl

The crystal structure of a third polymorphic form of the known 4-(2,6-difluorophenyl)-1,2,3,5-dithiadiazolyl radical, C(7)H(3)F(2)N(2)S(2), is reported. This new polymorph represents a unique crystal-packing motif never before observed for 1,2,3,5-dithiadiazolyl (DTDA) radicals. In the two known polymorphic forms of the title compound, all of the molecules form cis-cofacial dimers, such that two molecules are pi-stacked with like atoms one on top of the other, a common arrangement for DTDA species. By contrast, the third polymorph, reported herein, contains two crystallographically unique molecules organized such that only 50% are dimerized, while the other 50% remain monomeric radicals. The dimerized molecules are arranged in the trans-antarafacial mode. This less common dimer motif for DTDA species is characterized by pi-pi interactions between the S atoms [S...S = 3.208 (1) A at 110 K], such that the two molecules of the dimer are related by a centre of inversion. The most remarkable aspect of this third polymorph is that the DTDA dimers are co-packed with monomers. The monomeric radicals are arranged in one-dimensional chains directed by close lateral intermolecular contacts between the two S atoms of one DTDA heterocycle and an N atom of a neighbouring coplanar DTDA heterocycle [S...N = 2.857 (2) and 3.147 (2) A at 110 K].

Isomerization of a lanthanide complex using a humming top guest template: a solid-to-solid reaction

SbPh3Cl2 is used to effect a dramatic rearrangment of the ligand sphere and “pancake bonding” in Ce(hfac)3(5′-Br-pyDTDA)2, by forming a 2 : 1 host–guest complex supported by numerous non-covalent contacts (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-; 5′-Br-pyDTDA = 4-(5′-bromopyrid-2′-yl)-1,2,3,5-dithiadiazolyl). The host–guest complex forms quantitatively in a solvent-free solid-to-solid reaction and crystals are grown by sublimation.

A bis(1,2,3-dithiazole) charge transfer salt with 2 : 1 stoichiometry; inhibition of association and generation of slipped -stacks

The first example of a charge transfer salt of a benzo-bridged bis(1,2,3-dithiazole) with 2 : 1 stoichiometry is reported; the steric bulk of the chlorines at the 3,6-positions of the benzene ring induces slipped -stacks of dimer radical cations

Sterically protected 1,2,3-dithiazolyl radicals: preparation and structural characterization of 4-chloro-5-pentafluorophenyl-1,2,3-dithiazolyl

Steric protection afforded by a pentafluorophenyl group at the 5-position facilitates the first isolation and structural characterization of a monocyclic 1,2,3-dithiazolyl as its S–S bonded dimer.

3,7-Bis(2-thienyl)-1,5,2,4,6,8-dithiatetrazocine

The title molecule, 3,7-bis(2-thienyl)-1,5,2,4,6,8-dithiatetrazocine, C 10 H 6 N 4 S 4 , is planar within 0.069 (5) A and crystallizes in the monoclinic space group P2 1 /c. There are two centrosymmetric molecules in the cell; these are stacked such that each eight-membered C 2 N 4 S 2 ring has a thienyl ring above and below it. The mean interplanar separation is 3.55 (2) A.