Towards molecular alloys: computational and experimental studies on (p-NCC6F4CNSeSeN)x(p-NCC6F4CNSSN)1-x.

The ß-phase of the radical p-NCC6F4CNSSN (1ß) crystallizes in the orthorhombic space group Fdd2 and orders as a canted antiferromagnet with TN = 36 K. Computational studies (B3LYP or M06-2X functional with the cc-pVTZ-PP(-F)+basis set) of the microscopic nearest-neighbour magnetic exchange coupling in 1ß and in the hypothetical isomorphous phase of the selenium radical p-NCC6F4CNSeSeN (2ß) revealed that replacement of S by Se should lead to a significant enhancement in the magnetic ordering temperature by ca. 20% (B3LYP) - 30% (M06-2X). Recrystallization of 2 from solution or via vacuum sublimation afforded only the known diamagnetic, dimeric phase, 2α. Computational studies indicated that both the molecular geometry and charge distribution for 1 and 2 are extremely similar and experimental approaches to form alloys of the general form 11-x2x were explored: attempts to cosublime 1 and 2in vacuo were unsuccessful, forming only 1ß due to the low volatility of 2. Crystallization of pure 1 by solution evaporation was found to afford polymorph 1α (triclinic, P1̄) selectively, irrespective of the solvent employed (CH2Cl2, MeCN, PhMe or THF) but 1α transformed to 1ß upon subsequent vacuum sublimation. Crystallization of 1 in the presence of 2 (up to 20 mol%) from solution evaporation was examined. At 20 mol% there was clear evidence for formation of both 1α and 2α as distinct crystallographic phases by powder X-ray diffraction (PXRD) but some evidence for doping of 2 into 1α at low concentration (≤15 mol percent) was observed. Attempts to sublime a sample of 10.920.1 led to phase separation with the isolation of needle-shaped crystals of pure 1ß characterized by X-ray diffraction.

Lanthanide complexes facilitate wound healing by promoting fibroblast viability, migration and M2 macrophage polarization.

A tridentate ligand LH3 ((2-hydroxy-3-methoxybenzylidene)-2-(hydroxyimino)propanehydrazide) comprising o-vanillin, hydrazone and oxime donor groups has been employed to prepare a series of tetranuclear Ln(III) complexes. The reaction of ligand LH3 with Ln(NO3)3 [Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er] in MeOH yielded Ln4(LH)6(MeOH)2 (Ln = Sm(1), Eu(2), Gd(3), Tb(4), Ho (6) and Er (7))] whereas the corresponding reaction with Dy(NO3)3 afforded Dy4(LH)4(LH2)2(OH)2 (5). All complexes were characterized by various analytical techniques including single crystal X-ray diffraction, IR spectroscopy, UV-Vis spectroscopy, and elemental analysis. To investigate the potential of these lanthanide complexes for wound healing applications, their effects on fibroblast viability, migration, and M2 macrophage polarization were evaluated. The cytotoxicity assessment revealed that complexes 2(Eu), 4(Tb), 5(Dy), and 7(Er) significantly enhanced fibroblast viability compared to the negative control (NC). In vitro wound healing assay demonstrated that complexes 2(Eu) and 7(Eu) substantially promoted fibroblast migration compared to the NC. Moreover, complex 2(Eu) exhibited significant anti-inflammatory effects by reducing the phagocytic ability of lipopolysaccharide (LPS)-stimulated macrophage cells and attenuating nitric oxide (NO) production. In conclusion, among the series of complexes tested, complex 2(Eu) displayed the most potent anti-inflammatory effect on macrophage cells, while simultaneously promoting fibroblast viability and migration. This unique combination of properties renders complex 2 (Eu) highly promising for wound healing applications.

Synthesis of a Carbene-Stabilized (Diphospha)aminyl Radical and Its One Electron Oxidation and Reduction to Nonclassical Nitrenium and Amide Species.

Herein, we report the synthesis of an acyclic carbene-stabilized diphospha(aminyl) PNP radical CAACMePNPCAACMe 4 (CAACMe = 1-[2,6-bis(isopropyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene) by a facile one-pot, seven-electron reduction of hexachlorophosphazene chloride [Cl3PNPCl3][Cl]. The PNP radical 4 features a conjugated framework with spin density primarily localized on the central nitrogen atom as well as the flanking carbenes. Unlike other tripnictogen radicals, 4 undergoes facile one-electron oxidation and reduction to yield nonclassical nitrenium and amide species [5]+ and [6]-, respectively. The cation [5]+ exhibits conformational flexibility in the solution state between the expected W-shaped geometry [5b]+ and a previously unobserved linear heteroallene-type structure [5a]+, which was characterized in the solid state. The equilibrium was explored both computationally and experimentally, showing that [5a]+ is favored over [5b]+ both enthalpically (ΔH = -2.9 × 103 ± 80 J mol-1) and entropically (ΔS = 4.2 ± 0.25 J mol-1 K-1). The formal amide [6]- displays remarkable flexibility in its coordination chemistry due to the presence of multiple Lewis basic centers, as evidenced by the structure of its potassium complex K262, which exhibits µ, κ-P, κ-P, and η3-PNP coordination modes. Protonation of [6]- leads to the formation of an amine 7, which features a trigonal planar geometry around nitrogen.

Lewis Acid Assisted Brønsted Acid Catalysed Decarbonylation of Isocyanates: A Combined DFT and Experimental Study.

An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di-carboxamidation products and benzoxazolone compounds.

Robust S4 ⋠⋠⋠O Supramolecular Synthons: Structures of Radical-Radical Cocrystals [p-XC6 F4 CNSSN]2 [TEMPO] (X=F, Cl, Br, I, CN).

Cocrystallization of the dithiadiazolyl (DTDA) radicals p-XC6 F4 CNSSN (X=F, Cl, Br, I, CN) with TEMPO afforded the 2 : 1 cocrystals [p-XC6 F4 CNSSN]2 [TEMPO] (1-5) whose structures all reflect a common S4 ⋅⋅⋅O supramolecular motif. The nature of this interaction was probed by DFT calculations (M06/aug-cc-pVDZ) on 1 which revealed that the enthalpy of formation of the [C6 F5 CNSSN]2 [TEMPO] supramolecular motif from [C6 F5 CNSSN]2 and TEMPO is substantial (-54.0 kJ mol-1 ). Electronic structure calculations revealed a TEMPO-based doublet S= 1 / 2 configuration as the ground state with limited spin density on the DTDA rings (2.4 %). The corresponding spin quartet state is +78.9 kJ mol-1 higher in energy. An atoms-in-molecules analysis reveals four bond critical points (BCPs) between the TEMPO O and the DTDA S atoms as well as additional BCPs between selected DTDA S atoms and methyl H atoms of the TEMPO molecule. Herein, the structures of 2-5 are considered within the context of a hierarchical view of competing and complementary intermolecular interactions; in particular, the established supramolecular CN⋅⋅⋅S-S synthon is sacrificed in order to form the new S4 ⋅⋅⋅O interaction.

The chemistry of dithietes, 1,2,5,6-tetrathiocins and higher oligomers.

The synthesis and reactivity patterns of the strained dithiete ring are compared with their dimeric tetrathiocin counterparts and higher oligomers, highlighting: (i) their cycloaddition chemistry with organic dienophiles as a route to sulfur-containing heterocycles; (ii) their oxidative addition chemistry to low valent transition metal complexes to generate transition metal dithiolate complexes and; (iii) the base-catalysed isomerizations between different dithiete oligomers.

Structures, properties and applications of Cu(II) complexes with tridentate donor ligands.

Tridentate ligands offer theree donor atoms to coordinate to metal ions. The remaining vacant coordination sites on the metal ions provided opportunities to implement additional co-ligands to generate complexes with desired properties. Herein we discuss selected examples of Cu(ii) complexes with tridentate ligands utilizing combinations of N, O, S, and Se donors, focusing on effects of ligand flexibility/rigidity on their coordination modes, properties and applications.

A short, versatile route towards benzothiadiazinyl radicals.

A family of substituted 1,2,4-benzothiadiazine 1-chlorides have been prepared by treatment of N-arylamidines in neat thionyl chloride at reflux. The S(iv) 1-chlorides are readily reduced under mild conditions to persistent 1,2,4-benzothiadiazinyl radicals which have been characterised by EPR spectroscopy and cyclic voltammetry. Crystallographic studies on isolated radicals indicate that the radicals dimerise via pancake bonding in the solid-state, resulting in spin-pairing and net diamagnetism.

Oxidative addition of tetrathiocins to palladium(0) and platinum(0): a route to dithiolate coordination complexes.

The preparation of a series of 4,4',5,5'-substituted benzo-fused 1,2,5,6-tetrathiocins X2C6H2S4C6H2X2 (1a-1g) were prepared from the reaction of S2Cl2 with 1,2-C6H4X2 (X = OMe, OEt; X2 = OCH2O, OCH2CH2O, OCH2CH2CH2O, MeNC([double bond, length as m-dash]O)NMe, O(CH2CH2O)4). The oxidative addition of 1a-1g to zero-valent Pd2dba3 or Pt2dba3 (dba = dibenzylideneacetone) in the presence of bis (diphenylphosphino)ethane (dppe) resulted in formation of the substituted mononuclear benzenedithiolate complexes M(L)(dppe) [L = dithiolate ligand; 2a-2g (M = Pd) and 3a-3g (M = Pt)] in 37-89% yield based on recrystallized material. Representative examples of M(L)(dppf) [dppf = bis-diphenylphosphinoferrocene; 4a, 4g (M = Pd) and 5g (M = Pt)] were prepared in a similar fashion. The structures of all derivatives were determined by X-ray diffraction, multinuclear NMR and elemental analysis. The reactivity of the two crown ether dithiolate complexes, 2g and 4g, with 1 equivalent of NaBPh4 led to isolation of the 1 : 1 complexes in which the Na+ cation is bound in the macrocyclic crown, [Na(2g)(MeOH)2][BPh4] and [Na(4g)][BPh4] whose structures were determined by X-ray diffraction. Electrochemical studies supported through DFT calculations on the crown ether derivatives revealed a series of ligand-based oxidation waves corresponding to the dithiolate ligand (and dppf for 4g and 5g) whose redox potentials were shifted by ca. +0.1 V on binding to Na+.

1,3-Carboboration of iodonium ylides.

Herein, we disclose the utilisation of iodonium ylides to access a range of boron dienolates. Heating of acyclic iodonium ylides in the presence of different aryl boranes leads to the formation of rare 1,3-carboboration products. This methodology could not be expanded to cyclic iodonium ylides which instead formed a Lewis acid-base adduct. Products proved to be remarkably stable under a wide range of conditions allowing for their long term storage.

Structure-property-reactivity studies on dithiaphospholes.

The reaction of either toluene-3,4-dithiol or benzene dithiol with phosphorus(iii) trihalides generates the corresponding benzo-fused 1,3,2-dithiaphospholes, RC6H3S2PX (R = Me (1), R = H (2); X = Cl, Br, I). The P-chloro-dithiaphospholes undergo: (a) halogen abstraction reactions with Lewis acids forming phosphenium cations; (b) substitution with LiHMDS base and; (c) reduction chemistry with sodium metal to generate the P-P σ-bonded dimer, (RC6H3S2P)2. Reduction catalysis of aldehydes with pinacolborane using dithiaphospholes is compared with their dioxaphosphole and diazaphosphole counterparts as pre-catalysts, revealing interesting differences in the reactivity of this series of compounds.

Inclusion and reactivity of main group radicals in the porous framework MIL-53(Al).

Inclusion of the dithiadiazolyl and diselenadiazolyl radicals PhCNEEN (E = S, Se) into the porous framework, Al(bdc)(OH) [MIL-53(Al); bdc = 1,4-benzenedicarboxylate] was achieved by vacuum sublimation. PXRD studies reveal the inclusion complexes adopt the orthorhombic space group Imma. Variable temperature PXRD studies coupled with thermal analysis reveal that for PhCNSSN@MIL-53(Al), radical elimination from the pores at elevated temperatures is accompanied by an opening of the pore channels. Radicals can also be extracted from the framework using an appropriate solvent. Oxidation of the radical guest within the host framework has been achieved with Cl2 or Br2 and led to complete radical oxidation (based on EPR studies) whereas the milder oxidant I2 leads to incomplete oxidation.

Probing through-space and through-bond magnetic exchange couplings in a new benzotriazinyl radical and its metal complexes.

The synthesis and characterization of a new chelating benzotriazinyl radical (Rad2) are described. Crystallographic studies coupled with SQUID magnetometry on Rad2 reveal the presence of discrete radical pairs which are antiferromagnetically coupled. The reaction of Rad2 with the 3d transition metal complexes M(hfac)2·xH2O (hfac- = hexafluoroacetylacetonate) led to mononuclear metal complexes of general formula M(hfac)2(Rad2) [M = Zn(ii) (1); Ni(ii) (2) and Co(ii) (3)] whose structures have been determined by single crystal X-ray diffraction. Compounds 1-3 are isostructural and crystallize in the monoclinic space group P21/n with two molecules in the asymmetric unit. In the case of the Zn(ii) complex (1) through-space intermolecular radicalradical antiferromagnetic exchange interactions viaπ*π* contacts are observed, whereas strong intramolecular through-bond metal-radical ferromagnetic interactions [J = +59.3(9) cm-1] are observed for the Ni(ii) complex (2). For the Co(ii) complex (3), computational and magnetic studies reveal substantial zero field splitting and ferromagnetic metal-radical interactions.

Slow magnetic relaxation in Dy2 and Dy4 complexes of a versatile, trifunctional polydentate N,O-ligand.

A tridentate ligand LH3 (C11H13N3O4) comprising o-vanillin, hydrazone and oxime donor groups has been employed to prepare a new class of di- and tetranuclear LnIII complexes. The reaction of LH3 with Ln(NO3)3·xH2O in the presence of a suitable base yields the dinuclear DyIII complex [Dy2(LH2)4(CH3OH)][NO3]2 (1) and the tetranuclear complexes [Dy4(LH)4(LH2)2(OH)2]·2H2O (2) and [Gd4(LH)4(LH2)2(OMe)2]·nH2O, (3). In these complexes, LH3 is either monodeprotonated (1) or a mixture of mono- and doubly-deprotonated ligands (2 and 3) binding lanthanide ions via Ndiazine, Ohydrazone, and Ovanillin donors, while the remaining vacant coordination sites are occupied by OMeOH (1), Ohydroxide (2) and methoxides (3). DC magnetic susceptibility studies on the isotropic tetranuclear GdIII complex (3) reveal weak antiferromagnetic exchange interactions between the LnIII ions. AC studies reveal that the dinuclear complex (1) exhibits field-induced slow relaxation of magnetization with Ueff = 43.4 K, whereas 2 is a single molecule magnet, exhibiting slow relaxation of magnetization under zero field below 18 K, which is modelled using a combination of Orbach (Ueff/kB = 26.7 K) and Raman relaxation processes.

Reactions of hydrazones and hydrazides with Lewis acidic boranes.

The reaction of (diphenylmethylene)hydrazone or 1,4-bis-hydrazone-ylidene(phenylmethyl)benzene with Lewis acidic boranes B(2,4,6-F3C6H2)3 or B(3,4,5-F3C6H2)3 generates the Lewis acid-base adducts. Alternatively, when (9H-fluoren-9-ylidene)hydrazone is employed several products were isolated including 1,2-di(9H-fluoren-9-ylidene)hydrazone, the 2 : 1 borane adduct of NH2-NH2 and the 1-(diarylboraneyl)-2-(9H-fluoren-9-ylidene)hydrazone in which one ArH group has been eliminated. The benzhydrazide starting material also initially gives an adduct when reacted with Lewis acidic boranes which upon heating eliminates ArH generating a CON2B heterocycle.

Exploring through-bond and through-space magnetic communication in 1,3,2-dithiazolyl radical complexes.

Reaction of the methyl-benzodithiazolyl radical (MBDTA) with M(hfac)2 complexes (M = Mn, Co, Zn) affords the complexes M(hfac)2(MBDTA)2. Strong antiferromagnetic exchange interactions are observed between M(ii) ions and the two S = 1/2 radicals (M = Mn, Co), whereas weak antiferromagnetic interactions are observed between radicals when using the diamagnetic Zn(ii) ion. Strong intermolecular exchange coupling is also evident in Mn(hfac)2(MBDTA)2 and attributed to π*-π* contacts between MBDTA radicals which are absent for the Co and Zn derivatives.

Crystal structure, shape analysis and bioactivity of new LiI, NaI and MgII complexes with 1,10-phenanthroline and 2-(3,4-dichlorophenyl)acetic acid.

Reactions of 1,10-phenanthroline (phen) and 2-(3,4-dichlorophenyl)acetic acid (dcaH) with Mn(CO3) (M = LiI, NaI and MgII; n = 1 and 2) in MeOH yield the mononuclear lithium complex aqua[2-(3,4-dichlorophenyl)acetato-κO](1,10-phenanthroline-κ2N,N')lithium(I), [Li(C8H5Cl2O2)(C12H8N2)(H2O)] or [Li(dca)(phen)(H2O)] (1), the dinuclear sodium complex di-µ-aqua-bis{[2-(3,4-dichlorophenyl)acetato-κO](1,10-phenanthroline-κ2N,N')sodium(I)}, [Na2(C8H5Cl2O2)2(C12H8N2)2(H2O)2] or [Na2(dca)2(phen)2(H2O)2] (2), and the one-dimensional chain magnesium complex catena-poly[[[diaqua(1,10-phenanthroline-κ2N,N')magnesium]-µ-2-(3,4-dichlorophenyl)acetato-κ2O:O'] 2-(3,4-dichlorophenyl)acetate monohydrate], {[Mg(C8H5Cl2O2)(C12H8N2)(H2O)2](C8H5Cl2O2)·H2O}n or {[Mg(dca)(phen)(H2O)2](dca)·H2O}n (3). In these complexes, phen binds via an N,N'-chelate pocket, while the deprotonated dca- ligands coordinate either in a monodentate (in 1 and 2) or bidentate (in 3) fashion. The remaining coordination sites around the metal ions are occupied by water molecules in all three complexes. Complex 1 crystallizes in the triclinic space group P-1 with one molecule in the asymmetric unit. The Li+ ion adopts a four-coordinated distorted seesaw geometry comprising an [N2O2] donor set. Complex 2 crystallizes in the triclinic space group P-1 with half a molecule in the asymmetric unit, in which the Na+ ion adopts a five-coordinated distorted spherical square-pyramidal geometry, with an [N2O3] donor set. Complex 3 crystallizes in the orthorhombic space group P212121, with one Mg2+ ion, one phen ligand, two dca- ligands and three water molecules in the asymmetric unit. Both dcaH ligands are deprotonated, however, one dca- anion is not coordinated, whereas the second dca- anion coordinates in a bidentate fashion bridging two Mg2+ ions, resulting in a one-dimensional chain structure for 3. The Mg2+ ion adopts a distorted octahedral geometry, with an [N2O4] donor set. Complexes 1-3 were evaluated against urease and α-glucosidase enzymes for their inhibition potential and were found to be inactive.

Structural, Magnetic, and Optical Studies of the Polymorphic 9'-Anthracenyl Dithiadiazolyl Radical.

The fluorescent 9'-anthracenyl-functionalized dithiadiazolyl radical (3) exhibits four structurally determined crystalline phases, all of which are monomeric in the solid state. Polymorph 3α (monoclinic P21/ c, Z' = 2) is isolated when the radical is condensed onto a cold substrate (enthalpically favored polymorph), whereas 3ß (orthorhombic P21 21 21, Z' = 3) is collected on a warm substrate (entropically favored polymorph). The α and ß polymorphs exhibit chemically distinct structures with 3α exhibiting face-to-face π-π interactions between anthracenyl groups, while 3ß exhibits edge-to-face π-π interactions. 3α undergoes an irreversible conversion to 3ß on warming to 120 °C (393 K). The ß-phase undergoes a series of reversible solid-state transformations on cooling; below 300 K a phase transition occurs to form 3γ (monoclinic P21/ c, Z' = 1), and on further cooling below 165 K, a further transition is observed to 3δ (monoclinic P21/ n, Z' = 2). Both 3ß â†’ 3γ and 3γ → 3δ transitions are reversible (single-crystal X-ray diffraction), and the 3γ → 3δ process exhibits thermal hysteresis with a clear feature observed by heat capacity measurements. Heating 3ß above 160 °C generates a fifth polymorph (3ε) which is distinct from 3α-3δ based on powder X-ray diffraction data. The magnetic behavior of both 3α and the 3ß/3γ/3δ system reflect an S = 1/2 paramagnet with weak antiferromagnetic coupling. The reversible 3δ ↔ 3γ phase transition exhibits thermal hysteresis of 20 K. Below 50 K, the value of χm T for 3δ approaches 0 emu·K·mol-1 consistent with formation of a gapped state with an S = 0 ground-state configuration. In solution, both paramagnetic 3 and diamagnetic [3][GaCl4] exhibit similar absorption and emission profiles reflecting similar absorption and emission mechanisms for paramagnetic and diamagnetic forms. Both emit in the deep-blue region of the visible spectrum (λem ∼ 440 nm) upon excitation at 255 nm with quantum yields of 4% (3) and 30% ([3][GaCl4]) affording a switching ratio [ΦF(3+)/ΦF(3)] of 7.5 in quantum efficiency with oxidation state. Solid-state films of both 3 and [3][GaCl4] exhibit emission bands at a longer wavelength (490 nm) attributed to excimer emission.

On the Design of Radical-Radical Cocrystals.

Formation of radical-radical cocrystals is an important step towards the design of organic ferrimagnets. We describe a simple approach to generate radical-radical cocrystals through the identification and implementation of well-defined supramolecular synthons which favor cocrystallization over phase separation. In the current paper we implement the structure-directing interactions of the E-E bond (E=S, Se) of dithiadiazolyl (DTDA) and diselenadiazolyl (DSDA) radicals to form close contacts to electronegative groups. This is exemplified through the preparation and structural characterization of three sets of radical cocrystals; the 2:2 cocrystal [PhCNSSN]2 [MBDTA]2 (4) [MBDTA=methyl benzodithiazolyl] and the 2:1 cocrystals [C6 F5 CNEEN]2 [TEMPO] (E=S, 5; E=Se, 6). In 4 the two types of radical are linked via bifurcated inter-dimer δ+ S⋅⋅⋅Nδ- interactions whereas 5 and 6 exhibit a set of five-centre δ+ E⋅⋅⋅Oδ- contacts (E=S, Se).

A novel bis-1,2,4-benzothiadiazine pincer ligand: synthesis, characterization and first row transition metal complexes.

Reaction of 2,6-dicyanopyridine with 2 equiv. of 2-(propylthio)benzenamine in the presence of lithium bis(trimethylsilyl)amide, followed by ring-closing oxidation with N-chlorosuccinimide affords the novel tridentate ligand, 2,6-bis-(1',2',4'-benzothiadiazinyl)pyridine (LH2). Electrochemical studies on the free ligand LH2 reveal a single well-defined 2e- oxidation process with E1/2 = +0.90 V. EPR studies of the in situ chemical oxidation of LH2 reveal the generation of a benzotriazinyl radical. Reactions of ligand LH2 with a range of divalent transition metal salts in either MeOH or MeCN in a 2 : 1 ratio at ambient temperatures afforded mononuclear complexes with general formula [M(LH2)2][X]2 (M = Mn, X = CF3SO3 (1); Fe, X = CF3SO3 (2); Fe, X = BF4 (3); Co, X = Cl (4); Ni, X = Cl (5); Zn, X = CF3SO3 (6)) and the 1 : 1 complex [Cu(LH2)(NO3)2] (7). In all cases the LH2 ligand binds in a tridentate N,N',N'' chelate fashion via benzothiadiazinyl NBTDA and pyridyl Npy atoms. The low spin FeII complexes (2 and 3) were implemented for NMR and UV-Vis solution studies of ligand reactivity as well as cyclic voltammetry which reveal two 1e-oxidation waves. The metal complexes 1-6 are discussed and reveal a range of geometries between octahedral and trigonal prismatic with the greatest deviation from octahedral symmetry apparent for ions with no crystal field stabilisation energy, i.e. d10 ZnII and high spin d5 MnII ions.