Synthesis and anticancer activities of 1,4-phenylene-bis-<Emphasis Type="Italic">N</Emphasis>-acetyl- and <Emphasis Type="Italic">N</Emphasis>-phenylpyrazoline derivatives

Novel 1,4-phenylene-bis-N-acetyl- (3a–h) and bis-N-phenylpyrazoline derivatives (4a–h) were obtained by addition of hydrazine hydrate and phenylhydrazine to bis-chalcone derivatives (1a–h) in acetic acid and acetic acid/ethanol for 4 and 8 h in reflux conditions, respectively. The structures of the obtained bis-N-acetylpyrazoline and bis-N-phenylpyrazoline derivatives were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopic methods and elemental analysis. Compounds 3a–h and 4a–h were investigated to evaluate their anticancer activities against C6 (rat brain tumor cells) and HeLa (human uterus carcinoma) in vitro using a dose-dependent assay from 5 to 100 μM with 5-fluorouracil (5-FU) as standard anticancer drug. Compound 3a showed higher cell-selective activity compared with 5-FU against HeLa cells. Compounds 3a–h (except 3d) were shown to have better activities than 5-FU against both cells, particularly at high concentration. Compound 4c showed higher cell-selective activity compared with 5-FU against C6 cells. Compound 3a may be particularly promising as an anticancer drug against HeLa cells.     

Bioactive compounds from <Emphasis Type="Italic">Smilax excelsa</Emphasis> L.

Phytochemical investigation of EtOAc extract of Smilax excelsa has led to isolation and structure elucidation of five compounds. The structures of these compounds are established by different spectroscopic techniques including 1D and 2D-NMR, HRMS and ECD spectroscopy. The compounds were: solanesol (1), violasterol A (2), trans-resveratrol (3), 5-O-caffeoylshikimic acid (4) and 6-O-caffeoyl-β-d-fructofuranosyl-(2-1)-α-d-glucopyranoside (5). The configuration of compound 2 was established by electronic circular dichroism (ECD) spectroscopy. Meanwhile the cytotoxicity and antibacterial activity of the compounds were evaluated by MTT and MIC assays. Compounds 1 and 2 showed promising inhibition on MCF-7 cell line with IC₅₀ of 161.6 and 190.0 µM, respectively. Also compounds 2 and 3 illustrated activity against Staphylococcus aureus with MIC values of 142.5 and 136.9 µM, respectively.     

Structural systematics and conformational analyses of an isomer grid of nine tolyl-<Emphasis Type="Italic">N</Emphasis>-pyridinylcarbamates

A 3 × 3 isomer grid of nine Methylphenyl-N-pyridinylcarbamates (CxxM) is reported with seven CxxM crystal structures at 294 K (xx = pp, pm, po, mp, op, om, oo; x = para-, meta-, ortho), where Cx = pyridinyl ring (as C₅NH₄NH-) and xM is representative of –C(=O)OC₆H₄CH₃. All seven carbamate crystal structures aggregate via N–H…N intermolecular interactions with the three CpxM carbamates having C(6) zigzag chains, CmpM with C(5) zigzag chains and three ortho-pyridine CoxM structures as hydrogen-bonded dimers with graph set \(R_{2}^{2}\) (8) and augmented by flanking C–H…O contacts. The CpoM crystal structure crystallises with 0.25 CHCl₃ per carbamate molecule and solvent channels aligning along the a-axis direction. Conformational analyses of the nine minimised CxxM structures in gas phase are detailed for comparisons with the solid-state structures and demonstrate similarities between both structural methods. The modelling results also demonstrate the problems associated with pendant ortho-groups sterically clashing in the CmoM and CooM structures and methods to find a reasonable estimate of the CxxM conformational landscape.     

Synthesis,spectroscopic characterization,crystal structures,and theoretical studies of (<Emphasis Type="Italic">E</Emphasis>)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone and (<Emphasis Type="Italic">E</Emphasis>)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone

Two thiosemicarbazones, (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone (24-MBTSC (1)) and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone (25-MBTSC (2)), derived from 2,4-dimethoxybenzaldehyde and 2,5-dimethoxybenzaldehyde, respectively, with thiosemicarbazide have been synthesized and their structures were characterized by elemental analyses, FT-IR, ¹H NMR spectroscopy, and X-ray single-crystal diffraction analysis. Molecular orbital calculations have been carried out for 1 and 2 by using an ab initio method (HF) and also density functional method (B3LYP) at 6-31G basis set. Compound 1 crystallizes in the monoclinic system, space group P2₁/c, with a = 8.1342(5) Å, b = 18.1406(10) Å, c = 8.2847(6) Å, β = 109.7258(17)°, V = 1150.75(12) Å³, and Z = 4, whereas compound 2 crystallizes in the orthorhombic system, space group Pbca, with a = 11.0868(6) Å, b = 13.1332(6) Å, c = 15.9006(8) Å, V = 2315.2(2) Å³, and Z = 8. The compounds 1 and 2 displays a trans-configuration about the C=N double bond.     

Molecular and crystal structure of 15-acetylsongorine and songoramine isolated from <Emphasis Type="Italic">Aconitum szechenyianum</Emphasis> Gay

Two napelline skeletal diterpenoid alkaloids 15-acetylsongorine, C₂₄H₃₃NO₄ I, and songoramine, C₂₂H₂₉NO₃ II, were first isolated from the roots of Aconitum Szechenyianum Gay. The crystal structures were determined by X-ray single-crystal diffraction analysis. The crystal I is the triclinic system with space group P1 having unit cell parameters of a = 9.360(8) Å, b = 11.593(9) Å, c = 11.830(16) Å, α = 113.223(15)°, β = 105.950(16)°, γ = 101.296(12)°, and Z = 2. Hydrogen bonds O–H···O and O–H···N joint the molecules into dimer. The crystal II belongs to the orthorhombic system with space group P2₁2₁2₁ having unit cell parameters of a = 8.950(2) Å, b = 13.272(3) Å, c = 15.454(4) Å and Z = 4. The O–H···O hydrogen bonding interaction links the molecule into linear chains. The distortion of rings of compound I and II were evaluated by calculation of the Cremer and Pople puckering parameters. The presence of the C–O–C bond in the compound II results in the changes of ring conformations compared with that of the compound I.     

Flavonoids from <Emphasis Type="Italic">Cirsium japonicum</Emphasis> var. <Emphasis Type="Italic">maackii</Emphasis> pappus as inhibitors of aldose reductase and their simultaneous determination

Aldose reductase is an enzyme in the polyol pathway which is associated in the progression of diabetic complications. In this study, we evaluated the inhibitory activity of Cirsium japonicum var. maackii pappus (CJP) against rat lens aldose reductase (RLAR). The ethanolic extract, fractions and isolated flavonoids were subjected to an RLAR assay. Isolation of chloroform (CHCl₃) and ethyl acetate (EtOAc) fractions led to the identification of four flavonoids: hispidulin (1), cirsimaritin (2), apigenin (3), and cirsimarin (4). The RLAR assay results suggested that the EtOAc fraction and flavonoids 1 and 3 promoted better AR inhibition than did TMG (control). The half-maximal inhibitory concentration (IC₅₀) of compounds 1 and 3 was 0.77 and 3.19 μM, respectively. A simultaneous determination of flavonoid content using HPLC–UV indicated that CJP contained large amounts of compounds 2 and 3 (1.65 and 1.84 mg/g, respectively). Flavonoids from Cirsium species have been widely reported to show various pharmacological activities. This study indicated that CJP has the potential to prevent diabetic complications and was a potential source of flavonoids.     

Features of self-organization of highly dilute solutions of (<Emphasis Type="Italic">S</Emphasis>)-, (<Emphasis Type="Italic">R</Emphasis>)-, and (<Emphasis Type="Italic">SR</Emphasis>)-methionines and related carbamides and glycolurils

Aqueous solutions of (S)-, (R)-, and (SR)-methionines (1–3); carbamide (4); (S)-, (R)-, and (SR)-N-carbamoylmethionines (5–7); glycoluril (8); and glycolurils containing (S)and (R)-methionine moieties (9 and 10) kept under natural and hypoelectromagnetic conditions were studied in comparison by a complex of physicochemical methods (dynamic and electrophoretic light scattering, conductometry, pH-metry, and dielcometry). The process of selforganization and the properties of dilute solutions (1.0?10^–15–10^–1 mol L^–1) of compounds 1–10 was shown for the first time to depend substantially on the structure of the solute and configuration of methionine (Met) enantiomers. In the series 1–3, the greatest ability to self-organization is observed for solutions of (SR)-Met in which supramolecular domains (1.0?10^–5–1.0?10^–1 mol L^–1) and nanoassociates (1.0?10^–11–1.0?10^–8 mol L^–1) are formed. The formation of nanoassociates in a concentration range of 1.0?10^–12–1.0?10^–6 mol L^–1 can be responsible for the appearance of nonmonotonic concentration dependences of the physicochemical properties of solutions of N-carbamoylmethionines 5–7, whereas the physicochemical properties are more pronounced in solution of (S)-N-carbamoylmethionine 5 than in solutions of 6 and 7. The strongest influence of the configuration of the Met enantiomer on the ability of solution to self-organization was revealed in a series of glycolurils 9, 10: solutions of 9 with the (S)-Met moiety are disperse systems in which nanoassociates are formed in a range of 1.0?10^–15–1.0?10^–5 mol L^–1, whereas in solutions of 10 with the (R)-Met fragment the ability to self-organization in the low-concentration range is absent.     

The role of substituents in a bidentate <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-chelating ligand on the substitution of aqua ligands from mononuclear Pt(II) complexes

The rate of substitution of aqua ligands from three mononuclear platinum(II) complexes, namely [Pt{2-(pyrazol-1-ylmethyl)pyridine}(H₂O)₂](ClO₄)₂, [Pt(H ₂ Py)]; [Pt{2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine}(H₂O)₂](ClO₄)₂, [Pt(dCH ₃ Py)] and [Pt{2-[(3,5-bis(trifluoromethyl)pyrazoly-1-ylmethyl]pyridine}(H₂O)₂](ClO₄)₂, [Pt(dCF ₃ Py)] by thiourea, N,N-dimethylthiourea and N,N,N′,N′-tetramethylthiourea, was studied in aqueous perchloric acid medium of constant ionic strength. The substitution reactions were investigated under pseudo-first-order conditions as a function of nucleophile concentration and temperature using UV/Visible and stopped-flow spectrophotometries. The observed pseudo-first-order rate constants, \( k_{{{\text{obs }}\left( {1/2} \right)}} \), for the stepwise substitution of the first and second aqua ligands obeyed the rate law: \( k_{{{\text{obs}}\left( {1/2} \right)}} = k_{{2 \left( { 1 {\text{st/2nd}}} \right)}} \left[ {\text{Nu}} \right] \). The first substitution reaction takes place trans to the pyrazole ligand, while the second entering nucleophile is stabilised at the reaction site trans to the pyridine ligand. The rate of substitution of the first aqua ligand from the complexes followed the order: Pt(dCF ₃ Py) > Pt(H ₂ Py) > Pt(dCH ₃ Py), while that of the second was Pt(H ₂ Py) ≈ Pt(dCF ₃ Py) > Pt(dCH ₃ Py). Lower pK _a values were found for the deprotonation of the aqua ligand cis to the pyrazole ring. Density functional theory calculations were performed to support the interpretation of the experimental results.     

Aggregation in isomeric imides: analysis of the weak interactions in six <Emphasis Type="Italic">N</Emphasis>-(benzoyl)-<Emphasis Type="Italic">N</Emphasis>-(2-pyridyl)benzamides

Crystal structures of 4-chloro-N-(4-chlorobenzoyl)-N-(2-pyridyl)benzamide (I) Clpod, 3-chloro-N-(3-chlorobenzoyl)-N-(2-pyridyl)benzamide (II) Clmod and 2-chloro-N-(2-chlorobenzoyl)-N-(2-pyridyl)benzamide (III) Clood together with three methylated analogues, Mpod, Mmod and Mood, are presented herein. The Clxod acyclic imides are produced from reacting the 4-/3-/2-chlorobenzoyl chlorides (Clx) with 2-aminopyridine (o), respectively, together with their benzamide analogues Clxo; the Mxod/Mxo triad are produced similarly and in good yield. The five Clxod, Mpod and Mmod structures adopt the open transoid conformations as expected, but Mood crystallises with cisoid oriented benzoyl groups, and this conformation was unexpected, though not unknown. Halogen bonding contacts and weak hydrogen bonding C-H···N/O/π contacts are noted in the structures lacking strong hydrogen bonding donor atoms/groups but possessing a variety of strong and weaker acceptor atoms/groups. For Clxod, contact studies show that both hydrogen and carbon account for a high percentage of elements (70–75%) on the molecular surface and being the most abundant have C···H forming 26–30% of the contacts. Contact enrichment ratios are an indicator of the likelihood of chemical species to form intermolecular interactions with themselves and other species. The C-H···N and C-H···O are the most enriched (with E_HN?>?2.15), indicating that these weak hydrogen bonds are the driving force in the Clxod crystal packing formation. For Mxod, the C···H contact type at 40–52% is the most abundant contact type and C-H···O and C-H···N weak hydrogen bonds dominate with enrichment values in the 1.48–1.78 range. In Mxod, N/O···N/O contacts are effectively absent, except for Mpod (0.2%, N···N contacts) and both H···H and C···C non-polar contacts are moderately impoverished while the C···H interactions are slightly enriched (E?=?1.1–1.21).     

Synthesis,antifungal and insecticidal activity of novel [1,2,4]triazolo[4,3-<Emphasis Type="Italic">a</Emphasis>]pyridine derivatives containing a sulfide substructure

A series of [1,2,4]triazolo[4,3-a]pyridine derivatives bearing a sulfide substructure was designed, synthesized and characterized via ¹H·NMR, ¹³C·NMR, IR and elemental analyses. Bioassay Results indicated some of the derivatives displayed good fungicidal activity on Rhizoctonia cerealis, moderated insecticidal activity against Plutella xylostella and good insecticidal activity on Helicoverpa armigera. The inhibitory effects of compounds 4g and 4u against Rhizotonia cerealis were 70.9% at 50 μg mL^?1; the IC₅₀ values of compounds 4d and 4s against Plutella xylostella were 43.87 and 50.75 μg mL^?1, respectively. And the IC₅₀ values of compounds 4d, 4q, and 4s on Helicoverpa armigera were 58.3, 77.14 and 65.31 μg mL^?1, respectively, which were better than that of commercial chlorpyrifos (103.77 μg mL^?1).     

Unusual Polymers Containing Alternating <Emphasis Type="Italic">s</Emphasis> and <Emphasis Type="Italic">d</Emphasis> Elements Connected by Bridging Pivalate

From tetrahydrofurane solutions containing Cu(II) or Co(II) and potassium pivalate (KPiv) (molar ratios Cu/K=1/10, Co/K=1/5) one can isolate polynuclear [K₃Co₂Piv₇(THF)₃] (1) and [K₆Cu₂Piv₁₀(HPiv)(THF)(H₂O)₂]\(\cdot\)2THF (2), respectively. In the solid state the structures of the compounds consist of alternating, oppositely winding helices with a step of 46.085 Å for 1 and 25.260 Å for 2. In 2, the bridging pivalates link the infinite helices into layers. For both compounds, an important peculiarity of the structure is wide separation of transition metal ions (at least 5.327 Å for 1 and 6.791 Å for 2). Due to the presence of excess KPiv in the reaction system, the Cu(II) and Co(II) ions do not “coalesce” into polynuclear complexes typically observed in transition metal pivalates; instead they form unusual polymer systems containing alternating atoms of s and d elements. For transition metal pivalates, this type of structure was found for the first time.     

Synthesis and crystal structures of tetraacetylethylenediamine and <Emphasis Type="Italic">N</Emphasis>-(2-ammoniumethyl)carbamate

Two ethylenediamine derivatives—N-(2-ammoniumethyl)carbamate HN(COO^?)CH₂CH₂N⁺H₃ (I) and tetraacetylethylenediamine (H₃CC(O))₂NCH₂CH₂N(C(O)CH₃)₂ (II) (synthesized for the first time)—have been synthesized and characterized by X-ray crystallography. Compounds I and II are isolated as minor admixtures upon an attempt to synthesize ethylenediamine complexes of lanthanum and neodymium nitrates, respectively. The crystals of I and II are monoclinic: a = 7.778 Å, b = 8.060 Å, c = 7.568 Å, β = 95.73°, Z = 4, space group P2₁/c (I); a = 5.946, b = 10.255, c = 9.343 Å, β = 95.72°, Z = 2, space group P2₁/c (II). The bond lengths and bond angles lie within the corresponding standard values. Compounds I and II have different conformations of the N-C-C-N ethylenediamine moiety: gauche in I and trans in II, and the corresponding torsion angles are equal to 66.6° and 180°, respectively.     

Phenolic constituents from <Emphasis Type="Italic">Alisma plantago</Emphasis>-<Emphasis Type="Italic">aquatica</Emphasis> Linnaeus and their anti-chronic prostatitis activity

Background

The plant Alisma plantago-aquatica Linnaeus, which is widely distributed in southwest of China, is the main material of traditional Chinese medicine “Zexie”. It was used as folk medicine for immune-modulation, anti-tumor, anti-inflammatory and antibacterial. Previous chemical studies on A. plantago-aquatica reported the identification of triterpenes, diterpenes, sesquiterpenes, steroids, alkaloids and phenolic acid. Terpenes and phenolic acid were regard as major secondary metabolites from this medicine plant.

Results

A new phenolic acid, plantain A (1), along with four known compounds (2–5) were isolated and identified from A. plantago-aquatica by extensive chromatographic and spectrometric methods. In the present study, the levels of TNF-α, IL-1β, COX-2, PEG2 and TGF-β1 were increased in model group rats, whereas on treatment with the isolated compound (1 and 4) at 50 mg/kg, there was a significant decrease in the cytokine levels. Therefore, the anti-CNP effect of 1 and 4 may be related to their anti-inflammatory properties.

Conclusions

A new phenolic acid and four known phenolic compounds were isolated from A. plantago-aquatica. Moreover, compounds 1 and 4 shows significant anti-chronic prostatitis activity in rats.

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Synthesis and structure of silicon-containing <Emphasis Type="Italic">N</Emphasis>-methyland <Emphasis Type="Italic">N</Emphasis>-benzoylamides of diisopropylphosphoric acid

Diisopropyl N-benzoyl-N-(trimethylsilyl)phosphoramidate reacts with ClCH₂SiMe₂Cl under mild conditions to form diisopropyl N-benzoyl-N-[(chlorodimethylsilyl)methyl]phosphoramidate (III). Diisopropyl N-methyl-N-(trimethylsilyl)phosphoramidate with ClCH₂SiMe₂Cl affords an N-transsilylation product which does not rearrange into diisopropyl N-[(chlorodimethylsilyl)methyl]-N-methylphosphoramidate (XV) even under severe conditions (4 h, 130°C). Compound XV was prepared by the reaction of diisopropyl phosphorochloridate with N-[(methoxydimethylsilyl)methyl]-N-methylamine followed by treatment of diisopropyl N-[(methoxydimethylsilyl)methyl]-N-methylphosphoramidate with boron trichloride. Analysis of experimental and calculated ²⁹Si chemical shifts points to a five-coordinate silicon atom in compound III and a fourcoordinate silicon atom in compound XV. According to B3LYP calculations with due regard to solvent effects, compound III is an isomer with a C=O→Si bond. By variation of substituents at silicon, phosphorus, and carbonyl carbon atoms, chelate structures with either C=O→Si or P=O→Si dative bonds can be obtained.     

1-Aryl-3-(1<Emphasis Type="Italic">H</Emphasis>-imidazol-1-yl)propan-1-ol esters: synthesis,anti-<Emphasis Type="Italic">Candida</Emphasis>potential and molecular modeling studies

Background

An increased incidence of fungal infections, both invasive and superficial, has been witnessed over the last two decades. Candida species seem to be the main etiology of nosocomial fungal infections worldwide with Candida albicans, which is commensal in healthy individuals, accounting for the majority of invasive Candida infections with about 30-40% of mortality.

Results

New aromatic and heterocyclic esters 5a-k of 1-aryl-3-(1H-imidazol-1-yl)propan-1-ols 4a-d were successfully synthesized and evaluated for their anti-Candida potential. Compound 5a emerged as the most active congener among the newly synthesized compounds 5a-k with MIC value of 0.0833 μmol/mL as compared with fluconazole (MIC value >1.6325 μmol/mL). Additionally, molecular modeling studies were conducted on a set of anti-Candida albicans compounds.

Conclusion

The newly synthesized esters 5a-k showed more potent anti-Candida activities than fluconazole. Compounds 7 and 8 revealed significant anti-Candida albicans activity and were able to effectively satisfy the proposed pharmacophore geometry, using the energy accessible conformers (E_conf?<?20 kcal/mol).

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Photochemistry of <Emphasis Type="Italic">N</Emphasis>-substituted salicylic acid amides

The products of photolysis of N-substituted salicylic acid amides, viz., 2-hydroxy-3-tert-butyl-5-ethylbenzoic acid N-(4-hydroxy-3,5-di-tert-butylphenyl)amide (1) and 2-hydroxybenzoic acid N-[3-(4-hydroxy-3,5-di-tert-butylphenyl)prop-1-yl]amide (2), in heptane were studied by optical spectroscopy and stationary and nanosecond laser photolysis (Nd: YAG laser, 355 nm). It was shown by the method of partial deuteration of amides 1 and 2 that they exist in both the unbound state and as complexes with intraand intermolecular hydrogen bond. Amides 1 and 2 are subjected to photolysis, which results in the formation of a triplet state and phenoxyl radicals RO? presumably due to the absorption of the second photon by the excited singlet state. The formation of radical products due to N–H bond ionization was not observed. The main channel of decay of the triplet state and radicals RO? is triplet–triplet annihilation and recombination (k _r ≈ 2.3?10⁸ L mol^–1 s^–1), respectively. The UV irradiation of compounds 1 and 2 leads to the excitation of the amide groups, and no formation of radical products due to N–H bond ionization was observed.     

Effective reduction of <Emphasis Type="Italic">p</Emphasis>-nitrophenol catalyzed by nickel(II) adamantane complexes

Two Ni(II) adamantane complexes, [Ni(bqad)Cl₂] (1) and [Ni(bpad)(dmbp)(H₂O)](ClO₄)₂·CH₃OH H₂O (2) (bqad = N,N′-bis(2-quinolinylmethyl) amantadine, bpad = N,N′-bis(2-pyridylmethyl)amantadine, dmbp = 5,5′-dimethyl-2,2′-bipyridine) have been synthesized and characterized by elemental analysis, infrared spectroscopy and single crystal X-ray diffraction. The nickel centers in complex 1 have a distorted tetragonal pyramidal geometry, while the coordination polyhedron of 2 can be described as a distorted octahedron. The reaction kinetics for reduction of p-nitrophenol to p-aminophenol catalyzed by these complexes has been investigated by UV–visible spectrophotometry. Complex 1 exhibits a higher turnover frequency of 1.4 min^?1 for the reduction of p-nitrophenol.     

Catalytic <Emphasis Type="Italic">N</Emphasis>-formylation for synthesis of 6-substituted-2-benzothiazolylimino-5-piperazinyl-4-thiazolidinone antimicrobial agents

A new class of piperazine-based 2-benzothiazolylimino-4-thiazolidinones has been efficiently prepared via highly accelerated N-formylation of N-isopropylpiperazine by the use of a mild heterogeneous catalyst, sulfated tungstate. Heterocyclization of N-(benzo[d]thiazol-2-yl)-2-chloroacetamides (3a–j) by use of NH₄SCN in ethanol under reflux efficiently furnished the intermediates 2-benzothiazolyliminothiazolidin-4-ones (4a–j). These were treated with 4-isopropylpiperazine-1-carbaldehyde (2) to prepare the final products 5a–j. The structures of the new derivatives were confirmed by elemental analysis and use of spectroscopic data (FTIR and ¹H NMR). Their pharmacological potential as promising antimicrobial agents was determined in vitro against bacteria and a fungus; the lowest minimum inhibitory concentrations (MIC) observed were in the range 4–8 µg/mL.     

Crystal and molecular structure of <Emphasis Type="Italic">tris</Emphasis>(<Emphasis Type="Italic">m</Emphasis>-chlorophenyl)phosphine selenide

The crystal and molecular structure of tris(m-chlorophenyl)phosphine selenide, C₁₈H₁₂Cl₃PSe (I), was investigated by X-ray diffraction (XRD) analysis. The trigonal rhombohedral structure of I (space group \(R\overline 3 c\), a = 14.110(2) Å, c = 32.360(4) Å, Z = 12) was solved by direct methods and refined by least squares in an anisotropic approximation (R = 0.029) for 1319 averaged measured reflections (CAD-4 automatic diffractometer, λCuK_α).     

Substitution of aqua ligands from <Emphasis Type="Italic">cis</Emphasis>-platinum(II) complexes bearing 2-(phenylthiomethyl)pyridine spectator ligands

Cis-Pt(II) complexes, namely [Pt{2-(phenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^Ph ), [Pt{2-(4-tert-butylphenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^{Ph( t -But)} ) and [Pt{2-(4-fluorophenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^PhF ), were synthesised and characterised. The pK _a1 and pK _a2 values of the complexes were determined titrimetrically. Substitution of the aqua ligands from these complexes by thiourea nucleophiles was studied at a pH of 2 and ionic strength of 0.1 M under pseudo-first-order conditions using stopped-flow and UV–visible spectrophotometric techniques. Substitution of the aqua ligands depends on both the nature and concentration of the incoming ligand, with low enthalpy and negative entropy of activation values. Substitution of the first and second aqua ligands occurs sequentially and fits the rate laws: k _{obs (1/2)} = k _(1/2) [Nu]. The second-order rate constant, k ₁, relates to the substitution trans to sulphur, while k ₂ is the second-order rate constant for the subsequent substitution of the aqua ligand trans to pyridine. The rate of substitution of the first aqua ligand decreases in the order: Pt(pyS ^{Ph( t -But)} ) > Pt(pyS ^PhF ) > Pt(pyS ^Ph ), while that of the second decreases in the order: Pt(pyS ^{Ph( t -But)} ) > Pt(pyS ^Ph ) > Pt(pyS ^PhF ), reflecting the influence of the substituents on the spectator ligands. ¹⁹⁵Pt NMR spectra of aged solutions of complexes with the thiourea nucleophile suggest a subsequent but rapid concentration-independent ring opening of the N,S-bidentate ligand to form a PtS ₄ species. The crystal structure of Pt(pyS ^PhF )Cl ₂ was elucidated by X-ray diffraction analysis.