6,7,6′,7′-Tetra­phenyl-2,2′-bi[1,3-dithia-5,8-diaza­cyclo­penta­[b]naphthalenyl­idene] chloro­form disolvate

The title compound, C42H24N4S4·2CHCl3, a symmetrical tetra­thia­fulvalene (TTF) derivative, was prepared by a tri­ethyl­phos­phite-mediated self-coupling reaction of 6,7-diphenyl-1,3-dithia-5,8-diaza­cyclo­penta­[b]napthalen-2-one. The asymmetric unit contains two TTF mol­ecules and four chloro­form solvent mol­ecules. Cl⋯Cl inter­actions [contact distances = 3.263 (1)–3.395 (2) Å] are present between the solvent mol­ecules, resulting in a tape along the bc plane. The crystal packing features weak C—H⋯Cl and C—H⋯N hydrogen bonds, resulting in the formation of a two-dimensional supramolecular network

Synthesis, molecular structure and supramolecular chemistry of a new nickel-quinoxaline dithiolate system [Bu<SUB>4</SUB>N]<SUB>2</SUB>[Ni(6,7-qdt)<SUB>2</SUB>] (6,7-qdt = quinoxaline-6,7-dithiolate) and comparison of its electronic and electrochemical properties with those of [Bu<SUB>4</SUB>N]<SUB>2</SUB>[Ni(qdt)<SUB>2</SUB>] (qdt = quinoxaline-2,3-dithiolate)

The new nickel bis(dithiolene) complex [Bu<SUB>4</SUB>N]<SUB>2</SUB>[Ni(6,7-qdt)<SUB>2</SUB>] (1) (6,7-qdt = quinoxaline-6,7-dithiolate) has been synthesized, starting from quinoxaline-6,7-dithiol, nickel chloride and tetrabutylammonium bromide in methanol. Compound 1 crystallizes in P2<SUB>1</SUB>/c space group (monoclinic system). Its crystal structure has been characterized by interesting C— H···S and C— H···N weak interactions resulting in a three dimensional supramolecular network. Complex 1 shows solvent sensitive absorption band (broad feature) in the visible region, which is attributed to charge transfer (CT) transition involving electronic excitation from a HOMO that is a mixture of dithiolate (Π) and metal (d) orbital character to a LUMO which is a Π<SUP>*</SUP> orbital of the dithiolate. This CT transition absorbs at low energy region in comparison to the CT band of the [Bu<SUB>4</SUB>N]<SUB>2</SUB>[Ni(qdt)<SUB>2</SUB>] in the visible region. Interestingly, compound 1 undergoes reversible oxidation at very low oxidation potential (E<SUB>1/2</SUB> = + 0.12 V vs Ag/AgCl) compared to that of [Ni(qdt)<SUB>2</SUB>]<SUP>2-</SUP> (E<SUB>1/2</SUB> = + 0.41 V vs Ag/AgCl) in MeOH solutions

Synthesis, structural characterization and electrochemical studies of [Fe<SUB>2</SUB>(μ-L)(CO)<SUB>6</SUB>] and [Fe<SUB>2</SUB>(μ-L)(CO)<SUB>5</SUB>(PPh<SUB>3</SUB>)] (L = pyrazine-2,3-dithiolate, quinoxaline-2,3-dithiolate and pyrido[2,3-b]pyrazine-2,3-dithiolate): towards modeling the active site of [FeFe]-Hydrogenase

The reaction of heterocyclic 1,2-ene-dithiol ligands, namely, pyrazine-2,3-dithiol (H<SUB>2</SUB>pydt), quinoxaline-2,3-dithiol (H<SUB>2</SUB>qdt) and pyrido[2,3-b]pyrazine-2,3-dithiol (H<SUB>2</SUB>ppdt) with Fe<SUB>2(</SUB>CO)<SUB>9</SUB> yields the '[FeFe]-hydrogenase' model complexes [Fe<SUB>2</SUB>{μ-pydt}(CO)<SUB>6</SUB>] (1), [Fe<SUB>2</SUB>{μ-qdt}(CO)<SUB>6</SUB>] (2) and [Fe<SUB>2</SUB>{μ-ppdt}(CO)<SUB>6</SUB>] (3), respectively. A further reaction of complexes 1, 2 and 3 with PPh<SUB>3</SUB> in the presence of equimolar amount of decarbonylating agent Me<SUB>3</SUB>NO in CH<SUB>3</SUB>CN at room temperature resulted in the formation of unsymmetrical mono-PPh<SUB>3</SUB>-substituted model complexes [Fe<SUB>2</SUB>{μ-pydt}(CO)<SUB>5</SUB>PPh<SUB>3</SUB>] (4), [Fe<SUB>2</SUB>{μ-qdt}(CO)<SUB>5</SUB>PPh<SUB>3</SUB>] (5) and [Fe<SUB>2</SUB>{μ-ppdt}(CO)<SUB>5</SUB>PPh<SUB>3</SUB>] (6), respectively. The complexes 1-6 were well characterized by routine elemental analysis, IR, <SUP>1</SUP>H NMR, <SUP>13</SUP>C NMR spectroscopy and unambiguously characterized by X-ray crystallographic analysis. IR spectroscopy and electrochemical analysis show that an increase of the electron- withdrawing character of the bridging ligands (where electron-withdrawing character is in the order of pydt<SUP>2-</SUP> &gt; ppdt<SUP>2-</SUP> ≥ qdt<SUP>2-</SUP>) leads to a decreased electron density at the iron centers, which yield a milder reduction potential and higher CO stretching frequencies. All the compounds 1-6 are further characterized by electrochemical studies

A nitrogen rich Ni(II)-dithiolate system exhibiting acid-base behavior: synthesis, supramolecular structure and spectroscopy of [Bu<SUB>4</SUB>N]<SUB>2</SUB>[Ni<SUP>II</SUP>(ppdt)<SUB>2</SUB>] (ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate)

The compound [Bu<SUB>4</SUB>N]<SUB>2</SUB>[Ni(ppdt)<SUB>2</SUB>] (1) (ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate) has been synthesized, starting from pyrido[2,3-b]pyrazine-2,3-dithiol, nickel chloride and tetrabutylammonium bromide in methanol. Compound 1 crystallizes in P2<SUB>1</SUB>/c space group (monoclinic system). Its crystal structure is characterized by interesting C-H···S and C-H···N supramolecular weak interactions. Its solution state has been described with acid-base (protonation-deprotonation) behavior, that has rarely been investigated for a metal-dithiolene system. Compound 1 is first instance of a metal-dithiolene compound that has three ring nitrogen on each dithiolate ligand. The pH dependent changes in the charge-transfer absorption band are attributed to the protonation on an imine nitrogen of the ppdt ligand. The complex is electrochemically quasi-reversible with an oxidation potential of E<SUB>1/2</SUB> = +0.46 V vs. Ag/AgCl in methanol

Concurrent estimation of lamivudine, tenofovir disoproxil fumarate, and efavirenz in blended mixture and triple combination tablet formulation by a new stability indicating RP-HPLC method

Abstract Background An easy, defined, rapid, and accurate reverse phase high-performance liquid chromatography method was developed and subsequently validated for the concurrent estimation of lamivudine, efavirenz, and tenofovir disoproxil fumarate in their pure blend and combined tablet formulation. An efficient and appropriate separation of the three analytes was attained with Zorbax eclipse XDB-Phenyl column, with a mobile phase of methanol: buffer (0.1% v/v formic acid in water) (73:27 v/v) at a flow rate of 1mL/min and isocratic elution by using 260nm as detection wavelength. Equal ratio of acetonitrile and water was used as diluent. Results The retention times of lamivudine, tenofovir disoproxil fumarate, and efavirenz were found at 2.6, 4.4, and 5.9 min respectively. The linear response for lamivudine, tenofovir disoproxil fumarate, and efavirenz was in the range of 15.0–45.0μg/mL, 15.0–45.0μg/mL, and 20.0–60.0 μg/mL respectively. The method validation was done in accordance to ICH guidelines and all validation parameters in compliance with ICH standards. The degradants produced by stress testing were well resolved from the peaks of active analytes, which stipulates the stability-indicating property of the method. Conclusion The method has the ability to separate lamivudine, efavirenz, and tenofovir disoproxil fumarate concurrently in blended powder and their combined tablet. All degradants produced by application of stress conditions were separated with high resolution and determined with good sensitivity that ensures the stability-indicating property of the method. Thus, the projected method has high probability to adopt in the pharmaceutical industrial sector. </jats:sec