Synthesis of Silver(I) Complexes Containing 3-Oxo-3-phenyl-2-(2-phenylhydrazono)propanal-Based Ligands as a Multifunction Platform for Antimicrobial and Optoelectronic Applications.

Toward multifunctionality, including antimicrobial and optoelectronic applications, herein, we reported the synthesis of a novel Ag(I) complex with 3-oxo-3-phenyl-2-(2-phenylhydrazono)propanal-based ligands including 3-(4-chlorophenyl)-2-[2-(4-nitrophenyl)hydrazono]-3-oxopropanal (named as "4A"), 3-(4-chlorophenyl)-2-[2-(4-methylphenyl)hydrazono]-3-oxopropanal (named as "6A"), and 3-(4-chlorophenyl)-3-oxo-2-(2-phenylhydrazono)propanal (named as "9A"). The synthesized compounds were characterized through FTIR, 1H NMR, and density functional theory (DFT). The morphological features and thermal stability were evaluated through transmission electron microscopy (TEM) and TG/DTA analysis. The antimicrobial activity of the synthesized Ag complexes was tested against various pathogens, including Gram-negative bacteria (Escherichia coli and Klebsiella pneumonia), Gram-positive bacteria (Staphylococcus aureus and Streptococcus mutans), and fungi (Candida albicans and Aspergillus niger). Results show that the synthesized complexes (Ag(4A), Ag(6A), and Ag(9A)) possess promising antimicrobial efficacy against various pathogens and are in good competition with several standard drugs as well. On the other hand, the optoelectronic features such as absorbance, band gap, and Urbach energy were examined by measuring the absorbance using a UV-vis spectrophotometer. The values of the band gap reflected the semiconducting nature of these complexes. The complexation with Ag resulted in a lowering band gap to match the apex of the solar spectrum. Such low band gap values are preferable for optoelectronic applications like dye-sensitized solar cells, photodiodes, and photocatalysis.

The anticancer and EGFR-TK/CDK-9 dual inhibitory potentials of new synthetic pyranopyrazole and pyrazolone derivatives: X-ray crystallography, in vitro, and in silico mechanistic investigations.

Treatment options for the management of breast cancer are still inadequate. This inadequacy is attributed to the lack of effective targeted medications, often resulting in the recurrence of metastatic disorders. Cumulative evidence suggests that epidermal growth factor receptor (EGFR-TK) and cyclin-dependent kinases-9 (CDK-9) overexpression correlates with worse overall survival in breast cancer patients. Pyranopyrazole and pyrazolone are privileged options for the development of anticancer agents. Inspired by this proven scientific fact, we report here the synthesis of two new series of suggested anticancer molecules incorporating both heterocycles together with their characterization by IR, 1H NMR, 13C NMR, 13C NMR-DEPT, and X-ray diffraction methods. An attempt to get the pyranopyrazole-gold complexes was conducted but unexpectedly yielded benzylidene-2,4-dihydro-3H-pyrazol-3-one instead. This unexpected result was confirmed by X-ray crystallographic analysis. All newly synthesized compounds were assessed for their anti-proliferative activity against two different human breast cancer cells, and the obtained results were compared with the reference drug Staurosporine. The target compounds revealed variable cytotoxicity with IC50 at a low micromolar range with superior selectivity indices. Target enzyme EGFR-TK and CDK-9 assays showed that compounds 22 and 23 effectively inhibited both biological targets with IC50 values of 0.143 and 0.121 µM, respectively. Molecular docking experiments and molecular dynamics simulation were also conducted to further rationalize the in vitro obtained results.Communicated by Ramaswamy H. Sarma.

Synthesis and greener pastures biological study of bis-thiadiazoles as potential Covid-19 drug candidates.

A novel series of bis- (Abdelhamid et al., 2017, Banerjee et al., 2018, Bharanidharan et al., 2022)thiadiazoles was synthesized from the reaction of precursor dimethyl 2,2'-(1,2-diphenylethane-1,2-diylidene)-bis(hydrazine-1-carbodithioate) and hydrazonyl chlorides in ethanol under ultrasonic irradiation. Spectral tools (IR. NMR, MS, elemental analyses, molecular dynamic simulation, DFT and LUMO and HOMO) were used to elucidate the structure of the isolated products. Molecular docking for the precursor, 3 and ligands 6a-i to two COVID-19 important proteins Mpro and RdRp was compared with two approved drugs, Remdesivir and Ivermectin. The binding affinity varied between the ligands and the drugs. The highest recorded binding affinity of 6c with Mpro was (-9.2 kcal/mol), followed by 6b and 6a, (-8.9 and -8.5 kcal/mol), respectively. The lowest recorded binding affinity was (-7.0 kcal/mol) for 6 g. In comparison, the approved drugs showed binding affinity (-7.4 and -7.7 kcal/mol), for Remdesivir and Ivermectin, respectively, which are within the range of the binding affinity of our ligands. The binding affinity of the approved drug Ivermectin against RdRp recoded the highest (-8.6 kcal/mol), followed by 6a, 6 h, and 6i are the same have (-8.2 kcal/mol). The lowest reading was found for compound 3 ligand (-6.3 kcal/mol). On the other side, the amino acids also differed between the compounds studied in this project for both the viral proteins. The ligand 6a forms three H-bonds with Thr 319(A), Sr 255(A) and Arg 457(A), whereas Ivermectin forms three H-bonds with His 41(A), Gly143(A) and Gln 18(A) for viral Mpro. The RdRp amino acids residues could be divided into four groups based on the amino acids that interact with hydrogen or hydrophobic interactions. The first group contained 6d, 6b, 6 g, and Remdesivir with 1-4 hydrogen bonds and hydrophobic interactions 1 to 10. Group 2 is 6a and 6f exhibited 1 and 3 hydrogen bonds and 15 and 14 hydrophobic interactions. Group 3 has 6e and Ivermectin shows 4 and 3 hydrogen bonds, respectively and 11 hydrophobic interactions for both compounds. The last group contains ligands 3, 6c, 6 h, and 6i gave 1-3 hydrogen bonds and 6c and 3 recorded the highest number of hydrophobic interactions, 14 for both 6c and 6 h. Pro Tox-II estimated compounds' activities as Hepatoxic, Carcinogenic and Mutagenic, revealing that 6f-h were inactive in all five similar to that found with Remdesivir and Ivermectin. The drug-likeness prediction was carried out by studying physicochemical properties, lipophilicity, size, polarity, insolubility, unsaturation, and flexibility. Generally, some properties of the ligands were comparable to that of the standards used in this study, Remdesivir and Ivermectin.

Potential COVID-19 Drug Candidates Based on Diazinyl-Thiazol-Imine Moieties: Synthesis and Greener Pastures Biological Study.

A novel series of 1-aryl-N-[4-phenyl-5-(arylazo)thiazol-2-yl)methanimines has been synthesized via the condensation of 2-amino-4-phenyl-5-arylazothiazole with various aromatic aldehydes. The synthesized imines were characterized by spectroscopic techniques, namely 1H and 13C-NMR, FTIR, MS, and Elemental Analysis. A molecular comparative docking study for 3a-f was calculated, with reference to two approved drugs, Molnupiravir and Remdesivir, using 7BQY (Mpro; PDB code 7BQY; resolution: 1.7 A°) under identical conditions. The binding scores against 7BQY were in the range of -7.7 to -8.7 kcal/mol for 3a-f. The high scores of the compounds indicated an enhanced binding affinity of the molecules to the receptor. This is due to the hydrophobic interactions and multi-hydrogen bonds between 3a-f ligands and the receptor's active amino acid residues. The main aim of using in silco molecular docking was to rank 3a-f with respect to the approved drugs, Molnupiravir and Remdesivir, using free energy methods as greener pastures. A further interesting comparison presented the laydown of the ligands before and after molecular docking. These results and other supporting statistical analyses suggested that ligands 3a-f deserve further investigation in the context of potential therapeutic agents for COVID-19. Free-cost, PASS, SwissADME, and Way2drug were used in this research paper to determine the possible biological activities and cytotoxicity of 3a-f.

Design, synthesis, and greener pasture biological assessment of a novel nucleoside: 1-(α-D-ribofuranosyl)-6,7-difluoro-2-methyl-4-quinazolinone as an inhibitor of COVID-19 and Alzheimer's disease.

Synthesis of a new fluorinated nucleoside of 6,7-difluoro-2-methyl-4-quinazolinone was described. 2-Amino-4,5-difluorobenzoic acid 1 reacts with (CH3CO)2O followed by ammonia to form (1H)-6,7-difluoro-2-methyl-4-quinazolinone 3a. Ribosylation of a silylated 4 with l-O-acety1-2,3-5-tri-O-benzoyl-α-D-ribofuranose 5 forms a protected nucleoside 6 then unprotected from 6 to give a free nucleoside 7. Greener pasture biological docking of the cystine protease of COVID-19 [Mpro, code 7BQY, PDB] by novel nucleoside and fluoroquinazoline compounds is presented. LIGPLOT (2D) representations calculated for the same ligands are shown. A superposition of remdesivir approved medicine, N3 inhibitor, and our ligands docked together into the binding protein of 7BQY is also given for a fair comparison. The binding affinities of remdesivir, N3 inhibitor, the nucleoside 7, and fluoroquinazoline 3a, 3b compounds with 7BQY calculated under the same conditions are -7.7, -7.4, -7.6, -6.1, and -6.1 kcal mol-1, respectively. The high values were due to the existence of many hydrophobic interactions and hydrogen bonds between the ligands and the active amino acid residues of the receptor, indicating a promising candidate as a COVID-19 inhibitor. Pro Tox -II server showed that compound 7 has a similar feature to the approved antiviral drug remdesivir for COVID-19. Additionally, a fascinating molecular modeling investigation showed that our nucleoside demonstrated good binding inhibition of AChE enzyme towards advancing an efficient medication against Alzheimer's disease. Finally, DFT has been conducted to illustrate the MD results in terms of the molecular descriptor-based structural activity relationship calculated from FMOs.

A possible potential COVID-19 drug candidate: Diethyl 2-(2-(2-(3-methyl-2-oxoquinoxalin-1(2H)-yl)acetyl)hydrazono)malonate: Docking of disordered independent molecules of a novel crystal structure, HSA/DFT/XRD and cytotoxicity.

This study reports the synthesis, characterization and importance of a novel diethyl 2-(2-(2-(3-methyl-2-oxoquinoxalin-1(2H)-yl)acetyl)hydrazono)malonate (MQOAHM). Two independent molecular structures of the disordered MQOAHM have been established by XRD­single­crystal analysis in a ratio of 0.596(3)/0.404(3), MQOAHM (a) and MQOAHM (b), respectively. MQOAHM was characterized by means of various spectroscopic tools ESI-MS, IR, 1H &13C NMR analyses. Density Functional Theory (DFT) method, B3LYP, 6-311++G(d,p) basis set was used to optimize MQOAHM molecule. The obtained theoretical structure and experimental structure were superimposed on each other, and the correlation between them was calculated. The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) were created, and the energy gap between these orbitals was calculated. For analyzing intermolecular interactions, Molecular Electrostatic Potential (MEP) and Hirshfeld Surface Analysis were studied. For a fair comparative study, the two forms of the title compound were docked together with 18 approved drugs and N3 under precisely the same conditions. The disordered molecule structure's binding scores against 7BQY were -7.0 and -6.9 kcal/mol-1 for MQOAHM (a) and MQOAHM (b), respectively. Both the forms show almost identical superimposed structures and scores indicating that the disorder of the molecule, in this study, has no obvious effect. The high binding score of the molecule was attributed to the multi-hydrogen bond and hydrophobic interactions between the ligand and the receptor's active amino acid residues. Worth pointing out here that the aim of using the free energy in Silico molecular docking approach is to rank the title molecule compared to the wide range of approved drugs and a well-established ligand N3. The binding scores of all the molecules used in this study are ranged from -9.9 to -4.5 kcal/mol-1. These results and the supporting statistical analyses suggest that this malonate-based ligand merits further research in the context of possible therapeutic agents for COVID-19. Cheap computational techniques, PASS, Way2drug and ADMET, online software tools, were used in this study to uncover the title compound's potential biological activities and cytotoxicity.

New 1,2,3-Triazole Scaffold Schiff Bases as Potential Anti-COVID-19: Design, Synthesis, DFT-Molecular Docking, and Cytotoxicity Aspects.

Schiff bases encompassing a 1,2,3-triazole motif were synthesized using an efficient multi-step synthesis. The formations of targeted Schiff base ligands were confirmed by different spectroscopic techniques (FT-IR, 1H NMR, 13C NMR, and CHN analysis). The spectral data analysis revealed that the newly designed hydrazones exist as a mixture of trans-E and cis-E diastereomers. Densityfunctional theory calculations (DFT) for the Schiff bases showed that the trans-trans form has the lowest energy structure with maximum stability compared to the other possible geometrical isomers that could be present due to the orientation of the amidic NH-C=O group. The energy differences between the trans-trans on one side and syn-syn and syn-trans isomers on the other side were 9.26 and 5.56 kcal/mol, respectively. A quantitative structure-activity relationship investigation was also performed in terms of density functional theory. The binding affinities of the newly synthesized bases are, maybe, attributed to the presence of hydrogen bonds together with many hydrophobic interactions between the ligands and the active amino acid residue of the receptor. The superposition of the inhibitor N3 and an example ligand into the binding pocket of 7BQY is also presented. Further interesting comparative docking analyses were performed. Quantitative structure-activity relationship calculations are presented, illustrating possible inhibitory activity. Further computer-aided cytotoxicity analysis by Drug2Way and PASS online software was carried out for Schiff base ligands against various cancer cell lines. Overall, the results of this study suggest that these Schiff base derivatives may be considered for further investigation as possible therapeutic agents for COVID-19.

Novel 1,2,3-Triazole Derivatives as Potential Inhibitors against Covid-19 Main Protease: Synthesis, Characterization, Molecular Docking and DFT Studies.

The highly contagious nature of Covid-19 attracted us to this challenging area of research, mainly because the disease is spreading very fast and until now, no effective method of a safe treatment or a vaccine is developed. A library of novel 1,2,3-triazoles based 1,2,4-triazole, 1,3,4-oxadiazole and/or 1,3,4-thiadiazole scaffolds were designed and successfully synthesized. Different spectroscopic tools efficiently characterized all the newly synthesized hybrid molecules. An interesting finding is that some of the newly designed compounds revealed two isomeric forms. The ratio is affected by the size of the attached group as well as the type of the heteroatom forming the side ring attached to the central 1,2,3-triazole ring. The experimental spectroscopic data is in agreement with the DFT calculations at B3LYP 6-31G (d,p) with regard to the geometrical conformation of the prepared compounds. The DFT results revealed that the stability of one isomeric form over the other in the range of 0.057-0.161 Kcal mol-1. A docking study was performed using PyRx and AutoDockVina to investigate the activity of the prepared 1,2,3-triazoles as antiviral agents. Bond affinity scores of the 1,2,3-triazole derivatives were detected in the range of -6.0 to -8.8 kcal/mol showing binding to the active sites of the 6LU7 protease and hence could be anticipated to inhibit the activity of the enzyme. Verification of the docking results was performed using the Mpro alignment of coronaviruses substrate-binding pockets of COVID-19 against the ligands. As per these results, it can be proposed that the title hybrid molecules are acceptable candidates against COVID-19 for possible medicinal agents.

First COVID-19 molecular docking with a chalcone-based compound: synthesis, single-crystal structure and Hirshfeld surface analysis study.

The first example of molecular docking of the SARS-CoV-2 main protease for COVID-19 [Mpro, Protein Data Bank (PDB) code 7BQY] by a chalcone-based ligand, namely, (E)-1-(2,4-dichlorophenyl)-3-[4-(morpholin-4-yl)phenyl]prop-2-en-1-one, C19H17Cl2NO2, I, is presented. Two-dimensional (2D) LIGPLOT representations calculated for the inhibitor N3, viz. N-{[(5-methylisoxazol-3-yl)carbonyl]alanyl}-L-valyl-N1-((1R,2Z)-4-(benzyloxy)-4-oxo-1-{[(3R)-2-oxopyrrolidin-3-yl]methyl}but-2-enyl)-L-leucinamide, and 7BQY are included for comparison with our chalcone-based complexes. The binding affinity of our chalcone ligand with 7BQY is -7.0 kcal mol-1, a high value which was attributed to the presence of a hydrogen bond, together with many hydrophobic interactions between the drug and the active amino acid residues of the receptor. Docking studies were also performed, employing rigid and flexible binding modes for the ligand. The superposition of N3 and the chalcone docked into the binding pocket of 7BQY is also presented. The synthesis, single-crystal structure, Hirshfeld surface analysis (HSA) and spectral characterization of heterocyclic chalcone-based compound I, are also presented. The molecules are stacked, with normal π-π interactions, in the crystal.

Microwave-Assisted Synthesis of Mono- and Disubstituted 4-Hydroxyacetophenone Derivatives via Mannich Reaction: Synthesis, XRD and HS-Analysis.

An efficient microwave-assisted one-step synthetic route toward Mannich bases is developed from 4-hydroxyacetophenone and different secondary amines in quantitative yields, via a regioselective substitution reaction. The reaction takes a short time and is non-catalyzed and reproducible on a gram scale. The environmentally benign methodology provides a novel alternative, to the conventional methodologies, for the synthesis of mono- and disubstituted Mannich bases of 4-hydroxyacetophenone. All compounds were well-characterized by FT-IR, ¹H NMR, 13C NMR, and mass spectrometry. The structures of 1-{4-hydroxy-3-[(morpholin-4-yl)methyl]phenyl}ethan-1-one (2a) and 1-{4-hydroxy-3-[(pyrrolidin-1-yl)methyl]phenyl}ethan-1-one (3a) were determined by single crystal X-ray crystallography. Compound 2a and 3a crystallize in monoclinic, P21/n, and orthorhombic, Pbca, respectively. The most characteristic features of the molecular structure of 2a is that the morpholine fragment adopts a chair conformation with strong intramolecular hydrogen bonding. Compound 3a exhibits intermolecular hydrogen bonding, too. Furthermore, the computed Hirshfeld surface analysis confirms H-bonds and π⁻π stack interactions obtained by XRD packing analyses.

Synthesis and crystal structure of a new pyridinium bromide salt: 4-methyl-1-(3-phen-oxy-prop-yl)pyridinium bromide.

In the cation of the title mol-ecular salt, C15H18NO+·Br-, the pyridinium and phenyl rings are inclined to one another by 11.80 (8)°. In the crystal, the Br- anion is linked to the cation by a C-H⋯Br hydrogen bond. The cations stack along the b-axis direction and are linked by further C-H⋯Br inter-actions, and offset π-π inter-actions [inter-centroid distances = 3.5733 (19) and 3.8457 (19) Å], forming slabs parallel to the ab plane. The effects of the C-H⋯X- inter-action on the NMR signals of the ortho- and meta-pyridinium protons in a series of related ionic liquids, viz. 4-methyl-1-(4-phen-oxy-but-yl)pyridin-1-ium salts, are reported and discussed.

Crystal structure of a 1,1,2,2-tetra-chloro-ethane-solvated hydrazinecarbo-thio-amide compound.

The title compound, [(1-{4-[2-(2,4-di-hydroxy-phen-yl)diazen-1-yl]phen-yl}ethyl-idene)amino]-thio-urea, 1,1,2,2-tetra-chloro-ethane monosolvate, C15H15N5O2S·C2H2Cl4, was prepared from 4-(4-acetyl-phenyl-diazendi-yl)resorcinol and thio-semicarbazide and recrystallized from mixed solvents of tetra-chloro-ethane and n-hexane. 1H NMR and X-ray diffraction data are in support of the thione tautomeric form. The X-ray analysis shows the mol-ecule crystallizes as a zwitterion, with proton transfer from the nominal phenol to the azide group; the N-N bond length is 1.291 (5) Å, and an intra-molecular N-H⋯O hydrogen bond is formed. In the crystal, N-H⋯O, N-H⋯N and O-H⋯S hydrogen bonds connect the mol-ecules into a three-dimensional network. The tetra-chloro-ethane solvent mol-ecules are linked to this network through weak C-H⋯O linkages.

Crystal structure of 4-methyl-2,6,7-trioxa-1-phosphabi-cyclo-[2.2.2]octa-ne.

The title mol-ecule, C5H9O3P, has a bi-cyclo-[2.2.2] structure with the P atom at the prow and the bridge-head C atom, with the bonded methyl group, at the stern. The three six-membered rings in the bi-cyclo-[2.2.2] structure have essentially identical good boat conformations.

A new route for the synthesis of phosphate esters: 2,2'-[benzene-1,2-diylbis(oxy)]bis(5,5-dimethyl-1,3,2-dioxaphosphinane) 2,2'-dioxide.

Podand-type ligands are an interesting class of acyclic ligands which can form host-guest complexes with many transition metals and can undergo conformational changes. Organic phosphates are components of many biological molecules. A new route for the synthesis of phosphate esters with a retained six-membered ring has been used to prepare 2,2'-[benzene-1,2-diylbis(oxy)]bis(5,5-dimethyl-1,3,2-dioxaphosphinane) 2,2'-dioxide, C6H4{O[cyclo-P(O)OCH2CMe2CH2O]}2 or C16H24O8P2, (1), 2-[(2'-hydroxybiphenyl-2-yl)oxy]-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide, [cyclo-P(O)OCH2CMe2CH2O](2,2'-OC6H4-C6H4OH), (2), and oxybis(5,5-dimethyl-1,3,2-dioxaphosphinane) 2,2'-dioxide, O[cyclo-P(O)OCH2CMe2CH2O]2, (3). Compound (1) is novel, whereas the results for compounds (2) and (3) have been reported previously, but we record here our results for compound (3), which we find are more precise and accurate than those currently reported in the literature. In (1), two cyclo-P(O)OCH2CMe2CH2O groups are linked through a catechol group. The conformations about the two catechol O atoms are quite different, viz. one C-C-O-P torsion angle is -169.11 (11)° and indicates a trans arrangement, whereas the other C-C-O-P torsion angle is 92.48 (16)°, showing a gauche conformation. Both six-membered POCCCO rings have good chair-shape conformations. In both the trans and gauche conformations, the catechol O atoms are in the axial sites and the short P=O bonds are equatorially bound.

Crystal structure of (E)-1-{2-[(5,5-dimethyl-1,3,2-dioxaphosphinan-2-yl)-oxy]naphthalen-1-yl}-N-(4-fluoro-phen-yl)methanimine.

In the title compound, C22H21FNO3P, a 1,3,2-dioxaphosphinan-2-yloxy derivative, three O atoms are bonded in a trigonal-pyramidal manner to the P atom. The exocyclic P-O bond is significantly longer than the two endocyclic P-O bonds, viz. 1.6678 (12) Šcompared to 1.6046 (13) and 1.6096 (12) Å. The six-membered ring which includes the P atom has a chair conformation. The fluoro-phenyl ring is inclined to the naphthalene ring system by 24.42 (7)°. In the crystal, mol-ecules are linked via C-H⋯π inter-actions, forming slabs lying parallel to (10-1).

A Functionalized Heterocubane with Extensive Intermolecular Hydrogen Bonds.

A unique three-dimensional assembly is evident in the crystal structure of the cage compound 1: each molecule participates in the formation of eight O-H⋅⋅⋅O hydrogen bonds with neighboring molecules to form cavities with approximate dimensions of 3×3×8 Å3 . In contrast, compound 2, which contains the same framework structure, does not show this behavior in the crystal.

Cyclic Aminophosphites and -phosphoranes Possessing Six- and Higher-Membered Rings: A Comparative Study of Structure and Reactivity.

Aminophosphoranes 2 and 4-9 with a cyclohexylamino substituent and ring sizes varying from five to eight have been synthesized by oxidative addition reactions of cyclic aminophosphites with diols or 1,2-diketones. The reactivities of these phosphoranes are compared with those of the corresponding cyclic aminophosphites. The difference in hydrolytic pathways between amino- and analogous phenoxyphosphoranes is discussed. X-ray structures of two sets of compounds, (a) (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O) (1) and (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O)(1,2-O(2)C(6)Cl(4)) (2) and (b) (C(6)H(11)NH)P{O-(t-Bu)(2)C(6)H(2))(2)CH(2)} (3) and (C(6)H(11)NH)P{(O-(t-Bu)(2)C(6)H(2))(2)CH(2)}(1,2-O(2)C(6)H(4)).(1)/(2)Et(2)O (4.(1)/(2)Et(2)O) have been determined and geometrical parameters compared between the P(III) and the corresponding P(V) compounds. In 1, the six-membered ring has a chair conformation with the amino group axial; in 2, the six-membered ring is located apical-equatorial in a trigonal bipyramidal geometry and has a boat conformation. The eight-membered ring has a boat-chair conformation in 3, whereas the same ring has a tub conformation in 4.

Dinuclear and Tetranuclear Cages of Oxodiphenylantimony Phosphinates: Synthesis and Structures.

The novel dimeric compounds [Ph(2)Sb(O(2)PR(2))O](2).2CH(2)Cl(2) [R = cycl-C(6)H(11) (2) and cycl-C(8)H(15) (3)] have been synthesized by reacting diphenylantimony trichloride (1) with 3 mol equiv of silver acetate followed by 1 mol equiv of the phosphinic acid. By the same route under more stringent conditions to exclude moisture, the mixed phosphinate-acetate [Ph(2)Sb(O(2)P(C(6)H(11))(2))(O(2)CMe)](2)O (4) was isolated and characterized. Treatment of 2 with acetic acid/water affords the tetranuclear cage Ph(8)Sb(4)O(4)(OH)(2)(O(2)P(C(6)H(11))(2))(2).CH(3)COOH.CH(2)Cl(2) (5); it is possible to convert 5 to 2 by heating it with an excess of the phosphinic acid. Compounds 2, 3, and 5 have been characterized by X-ray structural analysis. All of them possess four membered Sb(2)O(2) rings with hexacoordinated antimony. In 5 the antimony atoms in the two Sb(2)O(2) rings are connected by oxo bridges on two sides to give an Sb(4)O(6) cage. These structures are correlated with those of known tin cages.