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Many cellular events are driven by changes in protein expression, measurable by mass spectrometry or antibody-based assays. However, using conventional technology, the analysis of transcription factor or membrane receptor expression is often limited by an insufficient sensitivity and specificity. To overcome this limitation, we have developed a high-resolution targeted proteomics strategy, which allows quantification down to the lower attomol range in a straightforward way without any prior enrichment or fractionation approaches. The method applies isotope-labeled peptide standards for quantification of the protein of interest. As proof of principle, we applied the improved workflow to proteins of the unfolded protein response (UPR), a signaling pathway of great clinical importance, and could for the first time detect and quantify all major UPR receptors, transducers and effectors that are not readily detectable via antibody-based-, SRM- or conventional PRM assays. As transcription and translation is central to the regulation of UPR, quantification and determination of protein copy numbers in the cell is important for our understanding of the signaling process as well as how pharmacologic modulation of these pathways impacts on the signaling. These questions can be answered using our newly established workflow as exemplified in an experiment using UPR perturbation in a glioblastoma cell lines.

Complex mass spectrometry based proteomics data sets are mostly analyzed by protein database searches. While this approach performs considerably well for sequenced organisms, direct inference of peptide sequences from tandem mass spectra, i.e., de novo peptide sequencing, oftentimes is the only way to obtain information when protein databases are absent. However, available algorithms suffer from drawbacks such as lack of validation and often high rates of false positive hits (FP). Here we present a simple method of combining results from commonly available de novo peptide sequencing algorithms, which in conjunction with minor tweaks in data acquisition ensues lower empirical FDR compared to the analysis using single algorithms. Results were validated using state-of-the art database search algorithms as well specifically synthesized reference peptides. Thus, we could increase the number of PSMs meeting a stringent FDR of 5% more than 3-fold compared to the single best de novo sequencing algorithm alone, accounting for an average of 11 120 PSMs (combined) instead of 3476 PSMs (alone) in triplicate 2 h LC-MS runs of tryptic HeLa digestion.

Tetranuclear, dinuclear and chain complexes involving some polyfunctional hydrazone and thio-carbohydrazone-based ligands are discussed. Ni(II) and Mn(II) [2 × 2] grids form with μ2-S and μ2-O bridges respectively, and are antiferromagnetically coupled (J = −167(5), −3.59(2) cm−1 respectively). With the Fe(II) based system oxidation to Fe(III) occurs, and a μ2-Ohydrazone bridged dimer results, with antiferromagnetic exchange between the S = 5/2 spin centers (J = −22.5(2) cm−1). In the case of Cu(II) the diazine group acts as a μ2-N–N bridge between Cu(II) centers in two cases involving a tetranuclear and a chain complex. Non-orthogonal bridging through N–N and carboxylate bridges leads to antiferromagnetic exchange in the tetranuclear case (J = −32.7(7), −16.1(7) cm−1 respectively) and ferromagnetic exchange in the chain complex due to orthogonal N–N bridging (J = 3.3(1) cm−1).

The current review provides up-to-date information on the structures, solution and solid state electron paramagnetic resonance (EPR), electronic and magnetic properties, and computational analysis of the novel 1,2,3,4-trithiazolium RCNSSS + radical cation. The stable 7π radical cation RCNSSS + , derived from RCNSSN by isoelectronic substitution of N by S + , is a rare example of a main group radical with ca. 96% of the spin density residing exclusively on the sulfur atoms. In the solid state it forms a great variety of structures, which, depending on the nature of the substituent group, range from dimeric to monomeric. This results in markedly different magnetic properties in which the magnetic coupling varies from −2100 cm −1 to −2 cm −1 , respectively. An important highlight in the chemistry of RCNSSS + is the preparation of (CNSSS + ) 2 2+ , which contains two radical centers directly joined by a single bond and is paramagnetic in all states, making it the only O 2 -like species in main group chemistry. Also important is the observation, by EPR, of a triplet excited state in the [RCNSSS] 2 2+ dimers and estimation of the dimerisation energy of the very weak inter-molecular S⋯S bonds as ca. −11 to −3 kJ/mol. The radical pairs [RCNSSS] 2 2+ also possess a high diradical character, ranging from 45 to 32%, thus lying on the borderline between conventional open shell and closed shell species.

The iron coordination chemistry of some polytopic hydrazone based ligands is examined. The complexes derive from a general self-assembly strategy, where ligand design can be used to devise specific polymetallic [n × n] grid architectures. However, as part of any complex equilibrium process, oligomeric entities can also occur, particularly when ligand tautomeric flexibility is considered, and examples of mononuclear, dinuclear, tetranuclear, and pentanuclear complexes have been observed within a related class of ligands. In addition, ligand site donor composition can lead to coordination spheres that stabilize both high spin Fe(II) and Fe(III) sites, with evidence for Fe(II) spin crossover. Structural and magnetic properties are examined, which reveal the presence of antiferromagnetic exchange in the polynuclear systems.

The tetratopic pyridazine-hydrazone ligand L2 is based on a design that successfully produces self-assembled [4 x 4] M II 16 (M = Mn, Cu) grids, but incorporates π-charge-rich, strong field bipy end groups. L2 forms an unusual incomplete "super" triangular Cu II 11 motif, dominated by the bipy ends. We now describe the incomplete Mn II 12 partial grid [Mn 12 (L2-2H) 6 (L-H) 2 (N(CN) 2 } 2 ].

Polytopic hydrazone-based ligands are discussed in the context of the design attributes of the ligand and the power of self-assembly as a methodology for the synthesis of polymetallic systems with specific and predetermined organization of the metal centers in a closely spaced bridged arrangement. Magnetic exchange coupling occurs as a result of the close proximity of the metal ions. Homometallic, heterometallic, and mixed-spin-state [n x n] (n = 2-5) square grids are highlighted and discussed in terms of their structural and magnetic properties. Antiferromagnetic, ferromagnetic, and ferrimagnetic examples are described.

Reaction of SNSSbF6 and DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone (1)) in SO2 solution in a 2:1 ratio afforded the dicycloaddition product 1(SNS)2(SbF6)2 · SO2 in 85% isolated yield. The dicycloaddition product 1(SNS)2(SbF6)2 · SO2 was fully characterized by IR, Raman, NMR, elemental analysis, and single crystal X-ray crystallography. The product of the site selective dicycloaddition of SNS+ at the nitrile functionalities of 1 represents the first structurally characterized ortho-bis-1,3,2,4-dithiadiazolylium salt which adopts a conformation that utilizes the intramolecular Sδ+–Oδ− electrostatic interactions. The reaction of 1 and SNS[Al(OC(CF3)4] in a 1:1 ratio yielded only the monocycloaddition product 1(SNS)[Al(OC(CF3)3)4] indentified by multinuclear 13C, 14N, 19F, 27Al NMR in SO2 solution. The assignment of the 13C NMR of 1(SNS)+ in SO2 solution, were supported by comparison of the calculated (MPW1PW91/6-31G∗) 13C NMR and experimental chemical shifts, and by comparison of the observed chemical shifts of the related 2(SNS)+ produced on reacting the mono-nitrile CDMQ (2-cyano-5,6-dichloro-3-methoxy-1,4-benzoquinone (2)) with SNS+ (as the SbF 6 - salt). The reaction of SNSSbF6 with TCNE (1,1,2,2-tetracyanoethylene (3)) gave the tri-cycloaddition product 3(SNS)3(SbF6)3 · SO2 (IR, Raman microscopy and X-ray crystallography) in 40% yield. The energetics of the cycloaddition reactions of SNS+ with 1–3 and other multifunctional unsaturated centers (e.g. HC C–CN, NC–CN, C ( CN ) 3 - , o,m,p-(CN)2C6H4, 1,3,5-(NC)3C6H3, 4–10, previously reported, see Chart 1 ), were estimated in the gas phase (MPW1PW91/6-31G∗), solution (PBE0/6-311G∗) and in the solid state by the ‘volume based thermodynamics’ (VBT) approach. The general thermodynamic trends associated with the stepwise cycloaddition of SNS+ with multifunctional nitriles were established. The 1:1 cycloaddition products were calculated to be stable in the gas phase and solution, while in the solid state the larger lattice enthalpy of the 1:2 salt, relative to twice that of the 1:1 salt, favored the 1:2 cycloaddition product.

A series of diradical containing salts CxF2x(CNSSS)(2)(center dot center dot 2+)(AsF6-)2 {X = 2, 1[AsF6](2); x = 3, 3[AsF6](2); x = 4, 2[AsF6](2)} have been prepared. 1[AsF6](2) and 2[AsF6](2) were fully characterized by X-ray, variable-temperature magnetic susceptibility, and solid-state EPR measurements, further allowing us to extend the number of examples of the family of rare 7 pi RCNSSS center dot+ radical cations. 1[AsF6](2): a = 6.5314(7) angstrom, b = 7.5658(9) angstrom, c = 9.6048(11) angstrom, alpha = 100.962(2)degrees, = 96.885(2)degrees, gamma = 107.436(2)degrees, triclinic, space group P (1) over bar, Z = 1, T = 173 K. 2[AsF6](2): a = 10.6398(16) angstrom, b = 7.9680(11) angstrom, c = 12.7468(19) angstrom, beta = 99.758(2)degrees, monoclinic, space group P2(1)/c, Z = 2, T = 173 K. In the solid-state, CxF2x(CNSSS)(2)(center dot center dot 2+) (x = 2, 4) formed one-dimensional polymeric chains of dications containing discrete centrosymmetric radical pairs in which radicals were linked by four centered two-electron pi*- pi* bonds [1(2+), d(S center dot center dot center dot S) = 3.455(1) angstrom; 2(2+), d(S center dot center dot center dot S) = 3.306(2) angstrom]. The exchange interactions in these bonds were determined to be -500 +/- 30 and -900 +/- 90 cm(-1), by variable temperature magnetic susceptibility measurements, respectively, providing rare experimental data on the singlet-triplet gaps in the field of thiazyl radicals. For 2[AsF6](2), the thermally excited triplet state was unambiguously characterized by EPR techniques [vertical bar D vertical bar = 0.0254(8) cm(-1), vertical bar E vertical bar = 0.0013(8) cm(-1)]. These experimental data implied a weakly associated nature of the radical moieties contained in the solids 1[AsF6](2) and 2[AsF6](2). Computational analysis of the dimerization process is presented, and we show that the 2c 4 electron pi*-pi* bonds in 1[AsF6](2) and 2[AsF6](2) have ca. 50% and 40% diradical character, respectively. In contrast, 3[AsF6](2)center dot SO2, containing diradical C3F6(CNSSS)(2)(center dot center dot 2+) with an odd number of CF2 spacers, showed magnetic behavior that was consistent with the presence of monomeric radical centers in the solid state.

Reaction of Cl3CN and F5C2CN with a 1:1 mixture of S4(AsF6)2 and S8(AsF6)2 affords the paramagnetic solids Cl3CNSSSAsF6 (1CCl3AsF6) and F5C2CNSSSAsF6 (1C2F5AsF6). Isotropic electron paramagnetic resonance spectra of 1CCl3AsF6 and 1C2F5AsF6 in SO2 consist of a single line with g = 2.01675 and 2.01580, respectively. The structure of 1CCl3AsF6 contains chains of radical cations with relatively close interchain interactions. In contrast, chains are isolated in 1C2F5AsF6. The magnetic behavior of both compounds was interpreted as that of 1D Heisenberg antiferromagnetic chains (1CCl3AsF6, J = -34 cm(-1), theta = -9 cm(-1), TIP = 0.00082, rho = 0.012; 1C2F5AsF6, J = -21 cm(-1), theta = -4.2 cm(-1), TIP = 0.00092, rho = 0.065). Density functional theory calculated and experimental magnetic coupling constants were in good agreement. The correlation between intermolecular S...S contacts and the strength of magnetic couplings was established.

wasperformed using a selected 436 nm line of a DRSh-500 mercury lampequipped with a water filter and a combination of glass filters.The EPR spectra were recorded on a Bruker EMX spectrometer (MWpower of 0.64 mW, modulation frequency of 100 kHz and modulationamplitude of 0.1 G). Spectral integration and simulation were performedusing the Win-EPR and Win-Sim programs, respectively. The radicalyields were determined by comparison of the integral intensities ofradicals with the integral intensity of a CuCl

Reduction of the radical-cation [*NSSNC-CNSNS][AsF(6)] with ferrocene affords the novel biradical *NSNSC-CNSSN* containing both 1,2,3,5- and 1,3,2,4-isomeric dithiadiazolyl rings. Biradicals form centrosymmetric dimers with pi(*)-pi(*) interactions between different isomeric rings. Biradical *NSNSC-CNSSN* is diamagnetic in the solid state (C = 0.00035, TIP = 6.5 x 10(-)(5) emu/Oe.mol); however, an increase in paramagnetism was observed upon grinding (C = 0.003, TIP = 4.2 x 10(-)(4) emu/Oe.mol).

A novel multitopic, two-pocket ligand HL(nit), containing the nitronyl nitroxide radical, has been designed for a self-assembled [2 × 2] grid system. HL(nit) is not stable in methanol and slowly undergoes a disproportionation, during which the nitronyl nitroxide radical converts to the diamagnetic amidino oxide. In situ reaction of HL(nit) with Cu(BF(4))(2) in methanol depending on the reaction time affords self-assembled [2 × 2] grids (L(nit))(2)(L)(2)Cu(II)(4)(BF(4))(4)·CH(3)OH (1) or (L(nit))(0.5)(L)(3.5)Cu(II)(4)(BF(4))(4)·CH(3)OH (2), in which L contains an amidino oxide arising from a 3-electron reduction of the nitronyl nitroxide radical. The percentages of stable radical in grids 1 and 2 as determined by X-ray are 50 and 12.5%, respectively. Structures 1 and 2 contain a six-coordinated distorted Cu(II) that is oxo-bridged at 140°. The nitronyl nitroxide radical coordinates via the oxo-atom of the N(+)-O(-) fragment in a chelating fashion and lies in the equatorial plane of the metal ion. The magnetic properties of 1 could be fitted to a 5-spin Hamiltonian with J(Cu-Cu) = +3.1 cm(-1) and J(Cu-Nit) = -278 cm(-1), while those of 2 to a 4-spin Hamiltonian with J(Cu-Cu) = +2.9 cm(-1). The Q-band EPR spectra of 1 and 2 recorded in solution at 20 K showed intricate anisotropic features of the Cu(II) ion and a much weaker signal of the -NO˙ fragment, associated with a strong Cu(II)-Nit antiferromagentic coupling. The DFT calculated (B3LYP/TZVP/6-31G*) magnetic coupling constants for the grid of 1 were J(Cu-Cu) = +5 cm(-1) and J(Cu-Nit) = -282 cm(-1), which are in very good agreement with the experimentally obtained values.

The ditopic carbohydrazide and thiocarbohydrazide based ligands H₂L1 and H₂L2 react with Co(II)(OAc)₂ to produce the homoleptic Co(II) molecular rectangles 1 and 2, containing either a mixture of high spin and low spin Co(II) sites or exclusively low spin Co(II) centers, respectively, with two mono-deprotonated ligands in a syn-conformation, and the other two doubly-deprotonated ligands in an anti-arrangement. The Co(II) centers are bridged by μ-O/S and μ-N-N groups, respectively. Magnetic susceptibility measurements indicate weak antiferromagnetic coupling between metal centers in 1 and 2, with room temperature magnetic moments of 6.6 and 3.4 μ(B), respectively, in good agreement with two S = 3/2 and two S = 1/2 centers for 1 and four S = 1/2 centers for 2. Reaction of H₂L1 and H₂L2 with Fe(II)(CF₃SO₃)₂ in the presence of a base leads to the formation of μ-O/S bridged homoleptic molecular squares 3 and 4, with the Fe(II) centers in high spin and low spin configurations, respectively at room temperature, as indicated from X-ray structural data and magnetic susceptibility measurements. However, in 3 one Fe(II) site undergoes spin crossover to a low spin state at about 150 K, while 4 stays diamagnetic in the full 2-300 K temperature range. Electrochemistry of 4 showed four distinct reversible red-ox waves associated with step-by-step one electron processes in the molecular square [-0.643 (ΔE(p) = 81 mV), -0.278 (ΔE(p) = 70 mV), +0.565 (ΔE(p) = 65 mV), ~1.1 V], associated with the Fe(II)/Fe(III) red-ox couples.

The reaction of NC-CN with a 1:1 mixture of S(4)(MF(6))(2) and S(8)(MF(6))(2) (M = As, Sb) (stoichiometrically equivalent to four "S(3)MF(6)" units) results in the quantitative formation of S(3)NCCNS(3)(MF(6))(2) [7(MF(6))(2)], which is the thermodynamic sink in this reaction. The Sb(2)F(11)(-) salt 7(Sb(2)F(11))(2) is prepared by the addition of an excess of SbF(5) to 7(AsF(6))(2). Crystal structure determinations for all three salts show that 7(2+) can be viewed as two R-CNS(3)(+) radical cations joined together by a C-C single bond. The two rings are coplanar and in a trans orientation due to electrostatic N(delta-)...S(delta+) interactions. The classically bonded alternative (quinoidal structure), in which the octet rule is obeyed, is not observed and is much higher in energy based on calculated estimates and a simple comparison of pi bond energies. Calculated molecular orbitals (MOs) support this, showing that the MO corresponding to the quinoidal structure lies higher in energy than the nearly degenerate singly occupied MOs of 7(2+). The vibrational spectra of 7(2+) in all salts were assigned based on a normal-coordinate analysis and theoretical vibrational frequencies calculated at the PBE0/6-31G* level. In the solid state, 7(2+) is a planar disjoint diradical with essentially degenerate open-shell singlet and triplet states. The disjoint nature of the diradical cation 7(2+) is established by magnetic susceptibility studies of the Sb(2)F(11)(-) salt doped in an isomorphous diamagnetic host material (CNSNS)(2)(Sb(2)F(11))(2) [10(Sb(2)F(11))(2)]. Intramolecular spin coupling is extremely weak corresponding to a singlet-triplet gap (DeltaE(ST) = 2J) of+/-2 cm(-1). CASPT2[12,12]/6-311G* calculations support a triplet ground state with a small singlet-triplet gap. The single-crystal electron paramagnetic resonance (EPR) of 7(Sb(2)F(11))(2) doped in 10(Sb(2)F(11))(2) is in agreement with the triplet state arising from the weak coupling between the unpaired electrons residing in p(pi) orbitals in each of the rings. Variable-temperature susceptibility data for bulk samples of 7(A)(2) (A = SbF(6)(-), AsF(6)(-), Sb(2)F(11)(-)) are analyzed by employing both 1D chain and 2D sheet magnetic models. These studies reveal significant intermolecular exchange approximating that of a 1D chain for the SbF(6)(-) salt with |J| = 32 cm(-1). The exchange coupling is on the same order of magnitude as that for the AsF(6)(-) salt, although in this case it is likely that there are complex exchange pathways where no particular one is dominant. Intermolecular exchange in the Sb(2)F(11)(-) salt is an order of magnitude weaker. In solution, the EPR spectrum of 7(2+) shows a broad triplet resonance as well as a sharp resonance that is tentatively attributed to a rotomer of the 7(2+)/anion pair, which is likely the origin of the green species given on dissolution of the red 7(2+) salts in SO(2)/AsF(3)/MF(5). We account for the many similarities between O(2) and 7(2+), which are the only simple nonsterically hindered nonmetal diradicals to retain their paramagnetism in the solid state. 7(2+) is also the first isolable, essentially sulfur-based diradical as evidenced by calculated spin densities.

This critical review surveys factors involved in the convergent self-assembly of square [n x n] (n = 2-5) polymetallic grids, using ligands with encoded coordination information appropriate to the metal ion's coordination algorithm. While entropic factors drive these reactions, other effects, including metal ion CFSE, ligand conformational character, electrostatic factors etc., can lead preferentially to non-grid oligomers. It will be of interest to the general supramolecular community, particularly coordination chemists attempting to create predetermined architectures, with applications oriented molecular based properties (86 references).

Polyfunctional hydrazone ligands with multidentate terminal donor groups offer metal ions many donor choices, and the coordination outcome depends mainly on the identity of the metal ion. Co(ii) and Ni(ii) prefer to adopt largely undistorted, six-coordinate geometries, while Cu(ii) can easily adapt to a variety of coordination situations (e.g. CN 4-6), and will optimize its coordination number and stereochemistry based on all the available donors. Ni(ii) and Co(ii) form simple [2 x 2] [M(4)-(micro(2)-O)(4)] square grids with such ditopic hydrazone ligands, and ignore other coordination options, while Cu(ii) tries to bind to all the available donors, and forms extended and 2D structures based on linked Cu(ii) triads rather than grids. Ni(ii) is also reluctant to compromise its desire to maximize its crystal field stabilization energy (CFSE) by binding to 'weak' ligands, and with a tetratopic pyrazole bis-hydrazone ligand it ignores the oxygen donors in favour of nitrogen, forming a novel trinuclear, triangular cluster. Also, reaction of a linear Ni(ii)(3) complex of a tetratopic pyridazine bis-hydrazone ligand with NiN(6) coordination spheres with Cu(ii), leads exclusively to a square Cu(12) grid based complex, and complete displacement of nickel. Structural and magnetic properties are highlighted, and metal-ligand interactions are discussed in detail.

A series of diradical containing salts CxF2x(CNSSS)2(**2+0(AsF6-)2 {x = 2, 1[AsF6]2; x = 3, 3[AsF6]2; x = 4, 2[AsF6]2} have been prepared. 1[AsF6]2 and 2[AsF6]2 were fully characterized by X-ray, variable-temperature magnetic susceptibility, and solid-state EPR measurements, further allowing us to extend the number of examples of the family of rare 7pi RCNSSS(*+) radical cations. 1[AsF6]2: a = 6.5314(7) A, b = 7.5658(9) A, c = 9.6048(11) A, alpha = 100.962(2) degrees , beta = 96.885(2) degrees , gamma = 107.436(2) degrees , triclinic, space group P, Z = 1, T = 173 K. 2[AsF6]2: a = 10.6398(16) A, b = 7.9680(11) A, c = 12.7468(19) A, beta = 99.758(2) degrees , monoclinic, space group P21/c, Z = 2, T = 173 K. In the solid-state, CxF2x(CNSSS)2(**2+) (x = 2, 4) formed one-dimensional polymeric chains of dications containing discrete centrosymmetric radical pairs in which radicals were linked by four centered two-electron pi*-pi* bonds [12+, d(S...S) = 3.455(1) A; 22+, d(S...S) = 3.306(2) A]. The exchange interactions in these bonds were determined to be -500 +/- 30 and -900 +/- 90 cm-1, by variable temperature magnetic susceptibility measurements, respectively, providing rare experimental data on the singlet-triplet gaps in the field of thiazyl radicals. For 2[AsF6]2, the thermally excited triplet state was unambiguously characterized by EPR techniques [/D/ = 0.0254(8) cm(-1), /E/ = 0.0013(8) cm(-1)]. These experimental data implied a weakly associated nature of the radical moieties contained in the solids 1[AsF6]2 and 2[AsF6]2. Computational analysis of the dimerization process is presented, and we show that the 2c 4 electron pi*-pi* bonds in 1[AsF6]2 and 2[AsF6]2 have ca. 50% and 40% diradical character, respectively. In contrast, 3[AsF6]2.SO2, containing diradical C3F6(CNSSS)2(**2+) with an odd number of CF2 spacers, showed magnetic behavior that was consistent with the presence of monomeric radical centers in the solid state.

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.

The synthetically useful SNSSbF 6 is prepared, in good yield, from the reactions of S 3 N 2 Cl 2 or S 3 N 3 Cl 3 with stoichiometric amounts of AgSbF 6 and S 8 in liquid SO 2 . SNSSbF 6 crystallizes monoclinic in space group C2/m (a = 9.740(2) A, b = 6.644(2) A, c = 5.334(1) A, β = 90.58(2)°, Z = 2). The crystal structure was determined by standard methods and refined to R 1 = 0.019 and wR 2 = 0.048. The structure consists of discrete linear centrosymmetric SNS + cations [S-N = 1.4871(10) A] and almost octahedral SbF 6 - anions, with weak cation-anion interactions. The lattice energy of SNSSbF 6 was determined from the volume-based method as 525 ′ 32 KJ mol - 1 and the heat of formation of SNSSbF 6 ( s ) has been estimated as -1566 ′ 24 KJ mol - 1 . The FT-IR, Raman, and 1 4 N NMR spectra are reported, as well as an in situ study of the reaction of S 3 N 2 Cl 2 with AsF 5 in SO 2 solution.

The synthetically useful SNSSbF 6 is prepared, in good yield, from the reactions of S 3 N 2 Cl 2 or S 3 N 3 Cl 3 with stoichiometric amounts of AgSbF 6 and S 8 in liquid SO 2 . SNSSbF 6 crystallizes monoclinic in space group C2/m (a = 9.740(2) A, b = 6.644(2) A, c = 5.334(1) A, β = 90.58(2)°, Z = 2). The crystal structure was determined by standard methods and refined to R 1 = 0.019 and wR 2 = 0.048. The structure consists of discrete linear centrosymmetric SNS + cations [S-N = 1.4871(10) A] and almost octahedral SbF 6 - anions, with weak cation-anion interactions. The lattice energy of SNSSbF 6 was determined from the volume-based method as 525 ′ 32 KJ mol - 1 and the heat of formation of SNSSbF 6 ( s ) has been estimated as -1566 ′ 24 KJ mol - 1 . The FT-IR, Raman, and 1 4 N NMR spectra are reported, as well as an in situ study of the reaction of S 3 N 2 Cl 2 with AsF 5 in SO 2 solution.

Both thermolysis and photolysis of 1,2,4λ4δ2,3,5- and 1,3λ4δ2,5,2,4-benzotrithiadiazepines in hydrocarbon solvents yielded stable 1,2,3- and 1,3,2-benzodithiazolyls, which can be considered as a particular case of a previously unmentioned trend of neutral polysulfur–nitrogen heterocycles to form thiazyl π-radicals.

Previously unknown 1,2,4,3,5-benzotrithiadiazepine 1 was prepared by 1∶1 condensation of Ph-NSN-SiMe3 with S2Cl2 followed by intramolecular ortho-cyclization of [Ph-NSN-S-S-Cl] intermediate, and hydrolyzed in pyridine to unusual macrocyclic 7H,14H-dibenzo[d,i][1,2,6,7,3,8]tetrathiadiazecine 2.

A high yield, one-pot synthesis of the 1,2,3,5-dithiadiazolyl radical NC-(CF2)4-CNSSN radical by reduction of the corresponding 1,3,2,4-dithiadiazolium salt is reported. In the solid state, the title compound is dimerized in trans-cofacial fashion with intra-dimeric Sdelta+...N(delta-) interactions of ca. 3.2 angstroms, and the dimeric units are linked by electrostatic -C triple bond N(delta-)...Sdelta+ interactions forming an infinite chain. Magnetic susceptibility measurements performed on the solid state sample indicate a magnetic moment of 1.8 microB per dimer (1.3 microB per monomer) at 300 K and a good fit to the Bleaney-Bowers model in the temperature range 2-300 K with 2J = -1500 +/- 50 cm(-1), g = 2.02(5), rho = 0.90(3)%, and TIP = 1.25(4) x 10(-3) emu mol(-1). The [NC-(CF2)4-CNSSN radical]2 dimer is the second example of a 1,2,3,5-dithiadiazolyl radical dimer with an experimentally detected triplet excited state as probed by solid-state EPR [2J = -1730 +/- 100 cm(-1), |D| = 0.0278(5) cm(-1), |E| = 0.0047(5) cm(-1)]. The value of the singlet-triplet gap has enabled us to estimate the "in situ" dimerization energy of the radical dimer as ca. -10 kJ mol(-1). The diradical character of the dimer was calculated [CASSCF(6,6)/6-31G*] as 35%. The title radical shows magnetic bistability in the temperature range of 305-335 K as probed by the solid-state EPR presumably arising from the presence of a metastable paramagnetic supercooled phase. Bistability is accompanied by thermochromic behavior with a color change from dark green (dimeric solid) to dark brown (paramagnetic liquid).