Perhalogenierte 1,2,3,5-Dithiadiazolium-Salze und 1,2,3,5-Dithiadiazole

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

SbPh₃Cl₂is used to effect a dramatic rearrangement of the ligand sphere and “pancake bonding” in Ce(hfac)₃(5′-Br-pyDTDA)₂by forming a 2 : 1 host–guest complex.

Electronic structure of disjoint diradical 4,4'-bis(1,2,3,5-dithiadiazolyl) thin films

The electronic structure of the thiazyl diradical, 4,4'-bis(1,2,3,5-dithiadiazolyl) (BDTDA), has been investigated by ultraviolet photoemission spectroscopy. Stacked BDTDA dimers showed an energy band dispersion of about 0.3 eV for the highest occupied molecular orbital in the direction of the surface normal of the BDTDA solid film. The pi-orbital overlap between the stacked dimers therefore evolves into a quasi one-dimensional energy band along the dimer stacking direction.

Characterization of the Diradical •NSNSC−CNSSN• and [NSNSC−CNSSN][MF6]n (n = 1, 2). The First Observation of an Excited Triplet State in Dimers of 7π −CNSSN• Radicals

Preparation and full characterization of the main-group diradical *NSNSC-CNSSN*, 8, the MF6- salt (As, Sb) of radical cation +NSNSC-CNSSN*, 8*+, and the AsF6- salt of the dication +NSNSC-CNSSN+, 82+, are presented. 8, a=6.717 (4), b=11.701(2), c=8.269(3) A, alpha=gamma=90, beta=106.69(3) degrees, monoclinic, space group P21/n, Z=4, T=203 K; 8SbF6, a=6.523(2), b=7.780(2), c=12.012(4) A, alpha=91.994(4), beta=96.716(4), gamma=09.177(4) degrees, triclinic, space group P, Z=2, T=198 K; 8[AsF6]2, a=12.7919(14), b=9.5760(11), c=18.532(2) A, alpha=gamma=90, beta=104.034(2) degrees, monoclinic, space group Pn, Z=6, T=198 K. Preparation of 8MF6 was carried out via a reduction of [CNSNS]2[MF6]2 (M=As, Sb) with either ferrocene or a SbPh3-NBu4Cl mixture. In the solid state, diamagnetic 8SbF6 contains centrosymmetric dimers [8*+]2 linked via two-electron four-centered pi*-pi* interactions with a thermally excited triplet state as detected by electron paramagnetic resonance (EPR). This is the first observation of a triplet excited state for a 7pi 1,2,3,5-dithiadiazolyl radical dimer. The singlet-triplet gap of the [-CNSSN*]2 radical pair was -1800+/-100 cm(-1) (-22+/-1 kJ/mol) with the ZFS components |D|=0.0267(6) cm(-1) and |E|=0.0012(1) cm(-1), corresponding to an in situ dimerization energy of ca. -11 kJ/mol. Cyclic voltammetry measurements of 8[AsF6]2 showed two reversible waves associated with a stepwise reduction of the two isomeric rings [E1/2 (+2/+1)=1.03 V; E1/2 (+1/0)=0.47 V, respectively]. 8MF6 (M=As, Sb) was further reduced to afford the mixed main-group diradical 8, containing two isomeric radical rings. In solution, 8 is thermodynamically unstable with respect to *NSSNC-CNSSN*, but is isolable in the solid state because of its low solubility in SO2. Likewise, 8SbF6, 8 is dimeric, with pi*-pi* interactions between different isomeric rings, and consequently diamagnetic; however, a slight increase in paramagnetism was observed upon grinding [from C=6.5(3)x10(-4) emu.K/mol and temperature-independent paramagnetism (TIP)=1.3(1)x10(-4) emu/mol to C=3.2(1)x10(-3) emu.K/mol and TIP=9.0(1)x10(-4) emu/mol], accompanied by an increase in the lattice-defect S=1/2 sites [from 0.087(1) to 0.43(1)%]. Computational analysis using the multiconfigurational approach [CASSCF(6,6)/6-31G*] indicated that the two-electron multicentered pi*-pi* bonds in [8*+]2 and [8]2 have substantial diradical characters, implying that their ground states are diradicaloid in nature. Our results suggest that the electronic structure of organic-radical ion pairs, for example, [TTF*+]2, [TCNE*-]2, [TCNQ*-]2, [DDQ*-]2, and related pi dimers, can be described in a similar way.

Mn(II) and Cu(II) Complexes of a Dithiadiazolyl Radical Ligand: Monomer/Dimer Equilibria in Solution

Complexes of the 4-(2'-pyridyl)-1,2,3,5-dithiadiazolyl radical bidentate ligand with bis(hexafluoroacetylacetonato)manganese(II) and with bis(hexafluoroacetylacetonato)copper(II) have been prepared. Unlike the previously reported cobalt(II) complex, these complexes form dimers via intermolecular S...S contacts in the solid state. The spectroscopic and magnetic properties of these species in the solid state and in solution are reported and compared to the previously reported Co(II) complex, with emphasis on the elucidation of the a monomer/dimer equilibrium in the solution. The electrochemical properties of these species in solution are also presented and discussed.

What's new in stable radical chemistry?

Many kinds of radicals are stable enough to isolate, handle, and store without any special precautions. The diversity in molecular architectures of these stable radicals is sufficiently large that the common factors governing radical stability/persistence, geometric and electronic structure, association/dimerization preferences, and reactivity have generally not been well articulated or appreciated. This review provides a survey of the major classes of stable or persistent organic/organomain group radicals with a view to presenting a unified description of the interdependencies between radical molecular structure and properties.

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.

Small molecule fixation by a dithiadiazolyl radical: X-ray crystal structures of (CF3C6H3FCNSSN)2and (CF3C6H3FCNSSN)2˙G (G = N2, Ar, CO2and SO2)

The title dithiadiazolyl radical, F3CC6H3FCNSSN (1) forms inclusion structures with small molecules (such as N2, CO2, Ar and SO2) when sublimed under partial atmospheres of the guest.

Thermal hysteresis in dithiadiazolyl and dithiazolyl radicals induced by supercooling of paramagnetic liquids close to room temperature: a study of F3CCNSSN and an interpretation of the behaviour of F3CCSNSCCF3

The trifluoromethyl-substituted dithiadiazolyl and dithiazolyl radicals, F3CCNSSN (1) and F3CCSNSCCF3 (2) associate through pi*-pi* covalent and electrostatic S delta+...N delta- interactions in the solid state, but melt with a dramatic volume increase to generate paramagnetic liquids; these radicals exhibit thermal hysteresis, which arises through a meta-stable super-cooled liquid state, close to room temperature.

Identification of the 1,3,2,4-Dithiadiazolyl RCNSNS(*) Radical Dimers in Solution, Their Dimeric Concerted Photochemically Symmetry-Allowed Rearrangement to 1,2,3,5-Dithiadiazolyl RCNSSN(*) by the Net Exchange of Adjacent Cyclic Sulfur and Nitrogen Atoms, and the Photolysis of RCNSNS(*)

The 1,3,2,4-dithiadiazolyl RCNSNS(*) radicals undergo an unprecedented concerted rearrangement to the thermodynamically more stable 1,2,3,5-dithiadiazolyl RCNSSN(*) radicals by the net exchange of adjacent cyclic sulfur and nitrogen atoms. The UV-visible spectra of RCNSNS(*) (R = Ph, p-O(2)NC(6)H(4), 3,5-(O(2)N)(2)C(6)H(3), CF(3)) in solution show bands at 250 nm (strong) and 680 nm (very weak) attributable to monomer and two dimer bands at 376 and 480 nm, the positions of which are independent of the substituents, providing direct identification of the radical dimers in solution. The dimerization equilibrium constant (K(298) approximately 0.7 for R = Ph) at room temperature was derived from the enthalpy and entropy changes for the dimerization of PhCNSNS(*) (DeltaH(d) degrees = -19.0 kJ/mol, DeltaS degrees = -66.5 J/mol) estimated by a variable-temperature ESR spectroscopic study. In addition, RCNSNS(*) (R = Bu(t), Ph) undergo an apparent unimolecular photolysis to RCN and possibly SNS(*) (analogue of ONO(*)). The photochemical rearrangement and dissociation (for R = Ph and 3,5-(O(2)N)(2)C(6)H(3)) were shown to proceed by irradiation of the radical dimer (376 and 480 nm) and monomer (250 nm), respectively. Thus, the radical rearrangement reasonably occurs via a concerted dimeric pathway shown by molecular orbital calculations (CNDO) to be photochemically symmetry-allowed. In addition, we propose that the radical dissociation proceeds via a concerted unimolecular photochemically symmetry-allowed process.