Geeta Hundal

Extraordinary Stability of Naphthalenediimide Radical Ion and Its Ultra-Electron-Deficient Precursor: Strategic Role of the Phosphonium Group

Stabilization of radical ions and highly electron-deficient systems under ambient conditions is of great significance. A new design concept is presented that applies the multifaceted features of the phosphonium group to achieve isolation of (a) the first naphthalenediimide (NDI) radical ion [(1a•+)BPh4(–)] as single crystals and (b) an ultra-electron-deficient NDI [(1a(2+))2BF4(–)] having the lowest LUMO level recorded for an NDI, overwhelming the formative tetracyanoquinodimethane (TCNQ) molecule. Both 1a•+ and 1a(2+) exhibit unprecedented stability to normal workup procedures, chromatography, and anion metathesis in open air. To our knowledge, this is the first instance where radical ions stable toward chromatography have been obtained, which is a noteworthy development in the field of synthetic radical chemistry. The crucial components of thermodynamic and kinetic stabilization, namely, the nonbonded P···O interaction, hypervalency, and propeller-like shape of the phosphonium groups in 1a(2+) and 1a•+, were substantiated by crystallography and theoretical studies. Natural bond orbital (NBO) calculations validated the P···O contact to be an nO → σP–C* orbital interaction. Spontaneous electron transfer reactions of 1a(2+) even in nonpolar solvents, anion−π interactions of 1a(2+) with the naphthalene core, and panchromism of 1a•+ are the other emergent properties. The high-yielding (∼90%) in situ synthesis of 1a•+ and the extraordinary stability fostered by the phosphonium group have the potential to turn hitherto unstable organic systems into a new genre of stable off-the-shelf systems.

Metal–heterocyclic thione interactions.: 12. Heterocyclic 2-thiolates of platinum(II) and palladium(II): the crystal structures of first examples of cis-[M(η1-S-pyridine-2-thiolato)2(L-L)] {M=Pt, Pd, L-L=1,2-bis(diphenylphosphino)ethane; M=Pt, L-L=1,2-bis(diphenylphosphino)ethene} complexes

Abstract A series of platinum(II) complexes of stoichiometry cis-[Pt(η1-S-C5H4NS)2(L-L)] were obtained from the reactions of platinum tetrachloride with pyridine-2-thione (C5H5NS) in the presence of Et3N base in an ethanol–benzene mixture followed by the addition of bis(tertiary phosphines), viz. {Ph2P–X–PPh2}, or phosphine chalcogenides {Ph2P–CH2–P(E)Ph2} {X(L-L)=(CH2)2(dppe) (1), CHCH(dppen) (2), (CH2)3(dppp) (3), (CH2)4(dppb) (4), E=S, dppmPS (5), E=Se, dppmPSe (6)}. Palladium(II) complexes, viz. [Pd(η1-S-C5H4NS)2(L-L)] {L-L=dppm (X=CH2) (7), dppe (8), dppp (9), dppmPS (10), dppmPSe (11)}, were prepared by reacting [PdCl2(diphosphines)] suspended in ethanol with C5H5NS in the presence of aqueous NaOH. All these compounds have been characterised with the help of analytical data [IR, far-IR, NMR (1H, 13C, 31P) spectroscopy] and X-ray crystallography (for compounds 1, 2 and 8). The geometry about each metal centre is distorted square planar with trans bond angles of: compound 1, P–Pt–S, 170.31(11), 173.18(10)°; compound 2, P–Pt–S, 168.97(5), 171.43(5)°; compound 8, P–Pd–S, 170.78(8), 171.83(8)°. The bite angles P(1)–M–P(2) and angles trans to bite angles, S(1)–M–S(2), are, respectively: compound 1, 85.68(11), 82.69(11)°; compound 2, 86.65(5), 84.01(6)°; compound 8, 85.19(8), 83.90(7)°. The dppe complexes (1 and 8) are isomorphous, monoclinic with space group C2/c, whereas the dppen complex is triclinic.These compounds represent the first examples of an interesting series of cis-platinum(II) and -palladium(II) derivatives of pyridine-2-thione containing chelating diphosphines and pendant pyridyl groups.

Synthesis, structure and biological activity of copper(II) complexes of 4-(2-pyridylmethyl)-1,7-dimethyl-1,4,7-triazonane-2,6-dione and 4-(2-pyridylethyl)-1,7-dimethyl-1,4,7-triazonane-2,6-dione

Four mononuclear copper(II) complexes 1-4 have been synthesized with two new N-functionalized macrocyclic ligands L(1) and L(2). All complexes are well characterized by various spectroscopic techniques, elemental analyses and conductivity measurements. Results suggest that Cu(II) ion has N(2)O coordination from ligand and S(2) from two coordinated solvent molecules (SCH(3)CN for 1 and 3 while CH(3)OH for 2 and 4). The crystal structure of a representative complex 3 strengthen the proposed formulations for other isostructural copper(II) complexes. The structure of 3 shows few interesting features including rare bent mode of the coordinated CH(3)CN molecules. All complexes were assayed for in vitro antimicrobial activity against clinically isolated resistant strains of Pseudomonas aeruginosa and Proteus vulgaris; and standard strains of Staphylococcus aureus, P. aeruginosa, Klebsiella planticola and Escherichia coli. Results indicate that the copper complexes possess notable antimicrobial properties with MIC values of 62.5-500 microg/ml. Studies on the U87 cancerous cell lines show potent cytotoxicity with IC(50) and IC(90) values of 2.9-93.5 and 30-250 microg/ml, respectively. In vitro toxicity tests demonstrate that all copper complexes are less cytotoxic than that of gentamycin on normal HEK cell lines. These copper complexes show the potential to act as antimicrobial and anticancer agent.

New tripodal and dipodal colorimetric sensors for anions based on tris/bis-urea/thiourea moieties

Seven neutral tripodal and dipodal receptors having mesitylene/triethylbenzene as core moiety, urea/thiourea as binding groups and p-nitrobenzene as signalling unit have been reported. The receptors act as selective colorimetric, naked eye sensors for small and spherical F− ion with some interference from tetrahedral ions. Thiourea derivatives form stable 1:1 H-bonded complexes with F− anion and to some extent with anions, whereas for urea derivatives, the recognition is simply based on acid–base reaction between ureidic protons and basic F− ions and is a completely reversible phenomenon. The pre-organisation of thiourea derivatives coupled with their high-intrinsic acidity is supposed to help them in the formation of strong H-bonded complexes with F− anion. The urea-based receptors do not respond at lower concentrations of the anion, but at higher concentrations, they undergo completely reversible deprotonation concomitant with a colorimetric change, with the production of stable [HF2]− anion.

Potential apoptosis inducing agents based on a new benzimidazole schiff base ligand and its dicopper(II) complex

Synthesis, characterization and antiproliferative activity of a new benzimidazole based Schiff base 2-(1-methyl-1-H-benzimidazol-2-yl)phenyl)imino)methyl)phenol (HL) and dicopper(II) complex [{Cu(L)NO3}2] (CuL) containing L− has been described. Both HL and CuL have been meticulously characterized by satisfactory elemental analyses, FT-IR, NMR, ESI-MS, electronic absorption and emission spectroscopy, and their structures unambiguously determined by X-ray single crystal analyses. Titration studies (absorption and emission) revealed interaction of the ligand and its dicopper(II) complex with DNA/BSA and stronger affinity of the CuL relative to HL. Binding of the HL and CuL with DNA/BSA have been validated by in silico studies and their cytotoxic effect on human breast cancer cell lines (MCF-7) by MTT assay. IC50 values (458 μM and 22 μM for HL, CuL) clearly suggested substantial cytotoxicity of the complex CuL toward MCF-7 compared to the ligand HL. Greater antiproliferative efficacy of the CuL in contrast to HL has been evidenced by fluorescence activated cell sorting (FACS) and AO/EB fluorescence staining. The possible mode of the apoptotic pathway for CuL has further been affirmed by reactive oxygen species (ROS) generation studies.

Neodymium 1D systems: targeting new sources for field-induced slow magnetization relaxation

Two non-isostructural homometallic 1D neodymium species displaying field-induced slow magnetization relaxations are presented together with theoretical studies. It is established that both systems are better described as organized 1D single molecule magnets (SMMs). Studies show great potential of Nd(III) ions to provide homometallic chains with slow magnetic relaxation.

The chemistry of pyridinethiols and related ligands, Part 9. Synthesis, spectroscopy and crystal structure of sulphur bridged dimeric [{η3-(O-μ-S)-1-oxopyridine-2-thione}(triphenylphosp hine)silver(I)]

Reaction of 1-hydroxypyridine-2-thione (HpyOS) in CHCl3 with Ag2CO3 suspended in CHCl3 under magnetic stirring followed by addition of PPh3 yields a product of stoichiometry: Ag(pyOS)(PPh3). The compound adopts a dimeric structure [Ag(pyOS)(PPh3)]2 (1) where each Ag atom acquires a distorted tetrahedral geometry by co-ordinating to one oxygen, two sulphur and one phosphorus atoms. The Ag2S2 core forms a parallelogram [Ag—S 2.507(1), 2.822(1)Å] with Ag—S—Ag and S—Ag—S angles of 74.8(1) and 105.2(1)°, respectively.

Copper(II)-Catalyzed Disulfide Scission—Stepwise Aerobic Oxidative Cleavage to Sulfinate and Sulfonate and Reductive Anaerobic Cleavage to Thiols

The Cu(II)-catalyzed oxidative and reductive cleavage of the disulfide bond of N-(2-(2-(2-picolinamido)phenyl)disulfanyl)phenyl)picolinamide, L, is reported for the first time. Aerobic oxidation with Cu(II) gives complete oxidation of S-S bond to sulfonates, whereas Ag(I) gives only partial oxidation up to sulfinates, in the absence of any other oxidizing agent, in tetrahydrofuran/water solution. The in situ generated sulfonate product forms a thermally stable, two-dimensional H-bonded polymeric complex with Cu(II) ions in two polymorphic forms. L in the presence of Cu(II), in an inert atmosphere, results in a reductive cleavage of the disulfide bond and an in situ formation of a new C-S bond. The latter forms a unique tetranuclear complex with Cu(II) employing deprotonated amide groups and bridging thiol and chloride atoms. The disulfide precursor and the products were characterized by X-ray crystallography and spectroscopic techniques.

Synthesis, spectroscopy, structures and antimicrobial activity of mixed-ligand zinc(II) complexes of 5-nitro-salicylaldehyde thiosemicarbazones

A series of new complexes of zinc(II) with 5-nitro-salicylaldehyde-N1-substituted thiosemicarbazones {5-NO2-C6H4(2-OH)-C2(H)N3–N2H–C1(S)–N1HR; H2L1–NHR, R = H, Me, Et, Ph: respective thio-ligands} using bipyridines/phenanthrolines (L′) as co-ligands have been synthesized and characterized using elemental analysis, infrared, NMR, electronic absorption and fluorescence spectroscopy and single crystal X-ray crystallography. Thio-ligands coordinate to the metal center as di-anions (O,N,S-L-NHR)2− in their complexes, [Zn(κ3-O,N,S-L-NHR)(κ2-N,N-L′)] {R, (N,N-L′): H, bipy 1, phen, 2; Me, bipy 3, phen 4; Et, bipy 5, phen, 6; Ph, bipy, 7, phen 8}. The geometries of complexes fall into three categories: distorted trigonal bipyramidal (1-molecule II, 5, 7); distorted square pyramidal (4, 6 and 8-molecule II) and geometry in between square pyramidal and trigonal bipyramidal (1-molecule I, 8-molecule II). These zinc(II) complexes have shown significant antimicrobial activity against Staphylococcus aureus (MTCC740), methicillin resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae (MTCC109), Shigella flexneri (MTCC1457), Salmonella typhimurium (MTCC741) and Candida albicans (MTCC227). The activity against MRSA and S. aureus is a significant development in antimicrobial investigations vis-a-vis lack of activity of gentamicin against MRSA or low antimicrobial activity against S. aureus as per literature reports. All complexes are active against K. pneumoniae and S. typhimurium, while complexes reported in the literature were found to be inactive. Complexes tested were found to be cytotoxic to microorganisms (bactericidal/fungicidal).

Heterometallic coordination polymers: syntheses, structures and heterogeneous catalytic applications

A metalloligand Na[Co(L1)2] (1) of the ligand H2L1 (N2,N6-bis(4,5-dihydrothiazol-2-yl)pyridine-2,6-dicarboxamide) offering appended thiazoline rings has been used for the synthesis of one-dimensional {Co3+–Zn2+} (2), {Co3+–Cd2+} (3) and {Co3+–Hg2+} (4) coordination polymers. 1 offers appended thiazoline rings having both soft sulphur and hard nitrogen donors. The crystal structures of 2 and 3 display the coordination of hard thiazoline-N donors to Zn2+ and Cd2+ ions. Interestingly, 4 illustrates the bonding through both hard thiazoline-N and soft thiazoline-S donors. The three heterometallic coordination polymers have been used as reusable heterogeneous catalysts for the ring-opening reactions of oxiranes and thiiranes; Knoevenagel condensation of benzaldehydes and benzothialdehydes; and cyanation reactions of aldehydes and carbothialdehydes. Our results demonstrate that the relative size and Lewis acidity of secondary metals potentially control the catalytic outcome via preferential interaction with the substrates.