Gordon D. McManus

Benzo-fused dithiazolyl radicals: from chemical curiosities to materials chemistry

Abstract Synthetic routes to benzo-fused 1,2,3- and 1,3,2-dithiazolylium salts are described. Their chemical stabilities and physical properties, especially their redox behaviour, are discussed. One electron reduction yields the corresponding benzo fused 1,2,3- and 1,3,2-dithiazolyl radicals. The electronic properties of the dithiazolyl ring are compared with a series of isoelectronic sulphur–nitrogen rings including dithiadiazolyl and trithiadiazolylium radicals. The ability to tune the redox behaviour of the dithiazolyl ring by changing the substituents, coupled with the lower dimerisation energy afforded by delocalisation of the unpaired electron makes these molecules attractive building blocks for the construction of molecular conductors and magnets. Recent results in this area are summarised.

Alignment of radicals into chains by a Markov mechanism for polarity formation

A theoretical concept for setting up 1D magnetic interactions between organic radicals aligned into chains within channels of inclusion compounds is presented by calculating collinear intermolecular binding energies using ab initio methods, followed by a Markov model to predict the characteristic length of chains. Experimentally, inclusion crystals providing radicals in channels of perhydrotriphenylene (PHTP) and tris(o-phenylenedioxy)cyclotriphosphazene (TPP) were obtained by co-crystallisation or in-diffusion of the 1,3,5-trithia-2,4,6-triazapentalenyl radical (TTTA).

Crystal engineering using polyphenols. Host-guest behaviour of planar ribbons in C-methylcalix[4]resorcinarene-4,4′-trimethylenedipyridine-methanol (1/2/0.5), and capture of 2,2′-bipyridyl molecules by paired calixarene bowls in C-methylcalix[4]-resorcinarene-2,2′-bipyridyl-methanol-water (1/1/1/1.16)

Co-crystallisation of the rccc isomer of C-methylcalix[4]resorcinarene 1 with 4,4′-trimethylenedipyridine from methanol yields a solvated 1:2 adduct 2 in which the resorcinarene acts as a quadruple donor and the dipyridines both act as double acceptors, in O-H‥N hydrogen bonds. The supramolecular structure consists of linear and nearly planar ribbons with the bowls of the resorcinarene units in one ribbon acting as hosts towards the -(CH 2 ) 3 - spacer units of a neighbouring ribbon, acting as guests. Co-crystallisation of the same resorcinarene 1 with 2,2′-bipyridyl yields a doubly solvated 1:1 adduct resorcinarene-2,2′-bipyridyl-methanol-water (1/1/1/1.16) 3. The resorcinarene, methanol and water molecules combine by means of multiple O-H‥O hydrogen bonds to form paired, essentially-planar two-dimensional nets in which centrosymmetric pairs of resorcinarene bowls act as self-assembled carcerands to form large cavities in which pairs of 2,2′-bipyridyl molecules are held by a combination of O-H‥N and C-H‥O hydrogen bonds.

Synthesis and characterisation of tetrafluorobenzo-1,3,2-dithiazolyl

Heterocyclic dithiazolyl (DTA) radicals recently have been shown to exhibit unusual physical properties including high magnetic ordering temperatures, as in the case of benzo-1,3,2-dithiadiazolyl1 (BDTA) (Tc = 11 K) and display of bistability2 at room temperature in trithiatriazapentalene (TTTA) among others. A new DTA salt [TFB-DTA]Cl (1) was prepared from C6F4(SH)2 using standard synthetic methods.2 Crystals were grown by sublimation (Figure 1). The radical was generated in situ by reduction of the salt with Ag powder in CH2Cl2. The X-band EPR spectrum of the radical exhibited a triplet of triplets due to coupling of the unpaired spin to one 14N nucleus (I = 1) and two 19F (I = 1/2) (giso = 2.0044, aiso = 11.0 G, aiso = 1.5 G). Further resolution of coupling to the remaining two F atoms could not be achieved (Figure 2).

Probing the Electronic Structure of the 1,3,5-Trithia-2,4,6-Triazapentalenyl Radical

The electronic structure of the 1,3,5-trithia-2,4,6-triazapentalenyl radical 1 was probed by means of EPR spectroscopy and DFT calculations. The unpaired spin density is delocalised asymmetrically over the entire molecule with 84% based on the SNS fragment and 22% on the NSN fragment.

Recent Studies on the Magnetic Behaviour of Thiazyl Radicals: Methyl-Benzodithiazolyl

The title radical (MBDTA) is characterised by X-ray diffraction and solid state magnetic measurements. It exhibits very strong antiferromagnetic exchange interactions which are modelled using an expression for a two-dimensional Heisenberg square-lattice.