PubMed Health⌕ Search

Biomedical subjects

H V Rasika Dias

Publications and source records attributed to H V Rasika Dias.

At least 19 recordsLinked to original sources
PubMed2006

Syntheses of highly fluorinated 1,3,5-triazapentadienyl ligands and their use in the isolation of copper(I)-carbonyl and copper(I)-ethylene complexes.

Fully fluorinated triazapentadienyl ligand [N{(C3F7)C(C6F5)N}2]- and the related [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]- have been synthesized in good yield via a convenient route and used in the isolation of three- and four-coordinate copper(I)-carbon monoxide complexes. They show fairly high nu(CO) values (>2100 cm(-1)), indicating the presence of electron-poor Cu sites. The copper(I)-ethylene adduct [N{(C3F7)C(C6F5)N}2]Cu(C2H4), featuring a three-coordinate Cu site, has also been synthesized using [N{(C3F7)C(C6F5)N}2]CuNCCH3 and C2H4.

Journal Article↗
PubMed2006

Intertrimer and intratrimer metallophilic and excimeric bonding in the ground and phosphorescent States of trinuclear coinage metal pyrazolates: a computational study.

The interactions present in cyclic trinuclear coinage metal pyrazolates were studied computationally. Cuprophilic interaction was found to bind the singlet ground state of the dimer of trimers [[Cu(Pz)](3)](2), overcoming electrostatic repulsion. The large variation in intertrimer separations found in the literature for coinage metal pyrazolates is consistent with the relatively weak metallophilic interaction. The emissive triplet excited-state geometry of [[M(Pz)](3)](2) is predicted by density functional calculations to show major geometric distortion caused by Jahn-Teller instability and excimeric M-M bonding. Large calculated Stokes' shifts, which are also observed for experimental models, are consistent with significant excited-state distortions for these materials. The major finding derived from the present study is that the intertrimer M...M contraction in the emissive T(1) state is much more than the intratrimer contraction in all [[M(Pz)](3)](2) models, giving rise to a lower T(1) --> S(0) phosphorescence energy in these models than in analogous monomer-of-trimer models. The observations made here point to a great potential for rationally tuning the emission properties of trinuclear coinage metal complexes through choice of the metal and ligands.

Journal Article↗
PubMed2006

Monomeric lithium triazapentadienyl complexes.

Treatment of 1,3,5-triazapentadienes [N{(C3F7)C(Mes)N}2]H and [N{(C3F7)C(Dipp)N}2]H (where Mes = 2,4,6-Me3C6H2; Dipp = 2,6-Pr(i)2C6H3) with n-BuLi in hexane, followed by the crystallization from hexane-THF mixture afforded the corresponding lithium 1,3,5-triazapentadienyl complexes as their THF solvates. X-Ray crystallographic analyses revealed that [N{(C3F7)C(Mes)N}2]Li(THF)2 and [N{(C3F7)C(Dipp)N}2]Li(THF) are monomeric in the solid state. [N{(C3F7)C(Mes)N}2]Li(THF)2 has a four-coordinate lithium center with a distorted tetrahedral geometry, and features a boat-shaped C2N3Li metallacycle. [N{(C3F7)C(Dipp)N}2]Li(THF) has a three-coordinate lithium atom and a planar, U-shaped C2N3 ligand backbone. The synthesis, solid-state structure, and 1H and 19F NMR spectroscopic details of [N{(C3F7)C(Mes)N}2]H are also reported.

Aza Compounds↗
PubMed2006

A mild, copper catalyzed route to conducting polyaniline.

The aniline dimer, N-(4-aminophenyl)aniline has been polymerized cleanly under mild conditions to obtain an emeraldine base form of polyaniline using [MeB(3-(Mes)Pz)3]CuCl as the catalyst and H2O2 as the oxidant, while the subsequent acidification of the emeraldine base gives the conducting emeraldine salt form of polyaniline.

Journal Article↗
PubMed2006

Antimicrobial properties of highly fluorinated silver(I) tris(pyrazolyl)borates.

Highly fluorinated tris(pyrazolyl)borate ligand [HB(3,5-(CF3)2Pz)3]- has been used in the isolation of air- and light-stable silver complex, [HB(3,5-(CF3)2Pz)3]Ag(OSMe2). It is a monomeric tetrahedral silver complex with an O-bonded dimethylsulfoxide ligand. The silver adduct [HB(3,5-(CF3)2Pz)3]Ag(OSMe2) and the related [HB(3,5-(CF3)2Pz)3] Ag(THF) (where OSMe2 = dimethyl sulfoxide; THF = tetrahydrofuran) show good antibacterial activity, and their antimicrobial efficacy against Staphylococcus aureus is greater than those of AgNO3 and silver sulfadiazine.

Anti-Infective Agents↗
PubMed2005

Metal effect on the supramolecular structure, photophysics, and acid-base character of trinuclear pyrazolato coinage metal complexes.

Varying the coinage metal in cyclic trinuclear pyrazolate complexes is found to significantly affect the solid-state packing, photophysics, and acid-base properties. The three isoleptic compounds used in this study are [[3,5-(CF3)2Pz]M]3 with M = Cu, Ag, and Au (i.e., Cu3, Ag3, and Au3, respectively). They form isomorphous crystals and exist as trimers featuring nine-membered M3N6 rings with linear two-coordinate metal sites. On the basis of the M-N distances, the covalent radii of two-coordinate Cu(I), Ag(I), and Au(I) were estimated as 1.11, 1.34, and 1.25 angstroms, respectively. The cyclic [[3,5-(CF3)2Pz]M]3 complexes pack as infinite chains of trimers with a greater number of pairwise intertrimer M...M interactions upon proceeding to heavier coinage metals. However, the intertrimer distances are conspicuously short in Ag3 (3.204 angstroms) versus Au3 (3.885 angstroms) or Cu3 (3.813 angstroms) despite the significantly larger covalent radius of Ag(I). Remarkable luminescence properties are found for the three M3 complexes, as manifested by the appearance of multiple unstructured phosphorescence bands whose colors and lifetimes change qualitatively upon varying the coinage metal and temperature. The multiple emissions are assigned to different phosphorescent excimeric states that exhibit enhanced M...M bonding relative to the ground state. The startling luminescence thermochromic changes in crystals of each compound are related to relaxation between the different phosphorescent excimers. The trend in the lowest energy phosphorescence band follows the relative triplet energy of the three M(I) atomic ions. DFT calculations indicate that [[3,5-(R)2Pz]M]3 trimers with R = H or Me are bases with the relative basicity order Ag << Cu < Au while fluorination (R = CF3) renders even the Au trimer acidic. These predictions were substantiated experimentally by the isolation of the first acid-base adduct, [[Au3]2:toluene]infinity, in which a trinuclear Au(I) complex acts as an acid.

Journal Article↗
PubMed2005

Fluorinated tris(pyrazolyl)borate ligands without the problematic hydride moiety: isolation of copper(I) ethylene and copper(I)-tin(II) complexes using [MeB(3-(CF3)Pz)3]-.

The thallium derivative of a fluorinated, B-methylated, tris(pyrazolyl)borate ligand, [MeB(3-(CF3)Pz)3]-, has been synthesized via a two-step process using the corresponding pyrazole, Li[MeBH3], and thallium(I) acetate. Reaction of [MeB(3-(CF3)Pz)3]Tl with CuBr in the presence of ethylene leads to [MeB(3-(CF3)Pz)3]Cu(C2H4). It is a thermally stable solid. [MeB(3-(CF3)Pz)3]Cu(C2H4) reacts with [(Bn)2ATI]SnCl to yield [MeB(3-(CF3)Pz)3]Cu<--Sn(Cl)[(Bn)2ATI], featuring an unsupported Cu(I)-Sn(II) bond [2.4540(4) A].

Journal Article↗
PubMed2005

Brightly phosphorescent trinuclear copper(I) complexes of pyrazolates: substituent effects on the supramolecular structure and photophysics.

Synthetic details, solid-state structures, and photophysical properties of a group of trimeric copper(I) complexes containing pyrazolate ligands are described. The reaction of copper(I) oxide and the fluorinated pyrazoles [3-(CF(3))Pz]H, [3-(CF(3)),5-(Me)Pz]H, and [3-(CF(3)),5-(Ph)Pz]H leads to the corresponding trinuclear copper(I) pyrazolates, {[3-(CF(3))Pz]Cu}(3), {[3-(CF(3)),5-(Me)Pz]Cu}(3), and {[3-(CF(3)),5-(Ph)Pz]Cu}(3), respectively, in high yield. The {[3,5-(i-Pr)(2)Pz]Cu}(3) compound was obtained by a reaction between [Cu(CH(3)CN)(4)][BF(4)], [3,5-(i-Pr)(2)Pz]H, and NEt(3). These compounds as well as {[3,5-(Me)(2)Pz]Cu}(3) and {[3,5-(CF(3))(2)Pz]Cu}(3) adopt trimeric structures with nine-membered Cu(3)N(6) metallacycles. There are varying degrees and types of intertrimer Cu...Cu interactions. These contacts give rise to zigzag chains in the fluorinated complexes, {[3-(CF(3))Pz]Cu}(3), {[3-(CF(3)),5-(Me)Pz]Cu}(3), {[3-(CF(3)),5-(Ph)Pz]Cu}(3), and {[3,5-(CF(3))(2)Pz]Cu}(3), whereas the nonfluorinated complexes, {[3,5-(Me)(2)Pz]Cu}(3) and {[3,5-(i-Pr)(2)Pz]Cu}(3) form dimers of trimers. Out of all the compounds examined in this study, {[3-(CF(3)),5-(Ph)Pz]Cu}(3) has the longest (3.848 Angstroms) and {[3,5-(Me)(2)Pz]Cu}(3) has the shortest (2.946 Angstroms) next-neighbor intertrimer Cu...Cu distance. The Cu...Cu separations within the trimer units do not vary significantly (typically 3.20-3.26 Angstroms). All of these trinuclear copper(I) pyrazolates show bright luminescence upon exposure to UV radiation. The luminescence bands are hugely red-shifted from the corresponding lowest-energy excitations, rather broad, and unstructured even at low temperatures, suggesting metal-centered emissions owing to intertrimer Cu...Cu interactions that are strengthened in the phosphorescent state. The {[3-(CF(3)),5-(Ph)Pz]Cu}(3) compound exhibits an additional highly structured phosphorescence with a vibronic structure corresponding to the pyrazolyl (Pz) ring. The luminescence properties of solids and solutions of the trimeric compounds in this study show fascinating trends with dramatic sensitivities to temperature, solvent, concentration, and excitation wavelengths.

Journal Article↗
PubMed2005

Neutral Cu4N12 and Ag4N12 metallacycles with a para-cyclophane framework assembled from copper(I) and silver(I) pyrazolates and pyridazine.

Trinuclear copper(I) and silver(I) pyrazolates {[3,5-(CF3)2Pz]M}3 (M = Cu and Ag) react with pyridazine to give neutral, tetranuclear metallacycles with a para-cyclophane core whereas benzo[c]cinnoline fails to break the cyclic pyrazolate trimers under similar conditions, and affords a metalla-propellane featuring both two- and three-coordinate metal sites.

Journal Article↗
PubMed2004

Silver(I) complexes of a sterically demanding fluorinated triazapentadienyl ligand [N((C3F7)C(Dipp)N)2]- (Dipp = 2,6-diisopropylphenyl).

Sterically demanding triazapentadiene [N((C3F7)C(Dipp)N)2]H affords the isolation of thermally stable, two- and three-coordinate silver complexes. The free ligand [N((C3F7)C(Dipp)N)2]H has a W-shaped ligand backbone in the solid state.[N((C3F7)C(Dipp)N)2]H reacts with silver(I) oxide in acetonitrile leading to CH(3)CNAg [N((C3F7)C(Dipp)N)2]HIt features a two-coordinate silver center and a kappa(1)-coordinated triazapentadienyl ligand. This silver acetonitrile complex serves as an excellent precursor to obtain thermally stable, silver isocyanide t-BuNCAg [N((C3F7)C(Dipp)N)2]Hand silver phosphine [[N((C3F7)C(Dipp)N)2]HAgPPh(3) adducts. IR spectroscopic data for the silver(I) isocyanide t-BuNCAg [N((C3F7)C(Dipp)N)2]Hshows nu(CN) at 2219 cm(-)(1). The silver ion coordinates to the triazapentadienyl ligand via the central nitrogen atom. The silver PPh(3) adduct,[N((C3F7)C(Dipp)N)2]HAgPPh(3), was synthesized by treating CH3CNAg [N((C3F7)C(Dipp)N)2]Hwith PPh(3). It displays relatively large Ag-P coupling in the (31)P NMR spectrum. The triazapentadienyl ligand in[N((C3F7)C(Dipp)N)2]HAgPPh(3) acts as a chelating kappa(2)-donor. The Ag-P bond is relatively short (2.3487(10) A).

Journal Article↗
PubMed2004

Copper(I) complexes of fluorinated triazapentadienyl ligands: synthesis and characterization of [N[(C3F7)C(Dipp)N]2]CuL (where L = NCCH3, CNBut, CO; Dipp = 2,6-diisopropylphenyl).

Sterically demanding triazapentadiene [N[(C3F7)C(Dipp)N]2] H has been synthesized in good yield. It features a W-shaped ligand backbone in the solid state. [N[(C3F7)C(Dipp)N]2]H reacts with copper(I) oxide in acetonitrile leading to [N[(C3F7)C(Dipp)N]2]CuNCCH3. This copper adduct serves as an excellent precursor to obtain thermally stable [N[(C3F7)C(Dipp)N]2]CuCNBut and [N[(C3F7)C(Dipp)N]2]CuCO. IR spectroscopic data of these copper(I) isocyanide (CN = 2176 cm(-1)) and copper(I) carbonyl (CO = 2109 cm(-1)) complexes indicate that the [N[(C3F7)C(Dipp)N]2]- ligand is a fairly weak donor.

Journal Article↗
PubMed2004

Oxidative rearrangement of imidazoles with dimethyldioxirane.

Tetrahydrobenzimidazoles, on treatment with dimethyldioxirane, rearrange to provide 5-imidazolones exclusively. These rearrangements proceed with a broad range of substrates and with good to excellent levels of diastereoselectivity. [reaction: see text]

Journal Article↗
PubMed2003

Blue phosphors of dinuclear and mononuclear copper(I) and silver(I) complexes of 3,5-bis(trifluoromethyl)pyrazolate and the related bis(pyrazolyl)borate.

The synthesis, structure, and photoluminescence properties are described for the three-coordinate mononuclear and dinuclear complexes [H(2)B(3,5-(CF(3))(2)Pz)(2)]M(2,4,6-collidine), M(1)(), and [[3,5-(CF(3))(2)Pz]M(2,4,6-collidine)](2), M(2)(), respectively (M = Cu; Ag). The solids exhibit bright blue phosphorescence, at room temperature for the copper compounds and at 77 K for all compounds. Ag(1)(), Cu(1)(), and Cu(2)() exhibit blue pyrazole-based structured emissions with short phosphorescence lifetimes, 10(1)-10(2) micros, due to an internal heavy-metal effect. Meanwhile, Ag(2)() exhibits curious multiple excitation-dependent emissions.

Journal Article↗
PubMed2003

Bright phosphorescence of a trinuclear copper(I) complex: luminescence thermochromism, solvatochromism, and "concentration luminochromism".

A photophysical study is reported for the trinuclear copper(I) complex {[3,5-(CF3)2Pz]Cu}3. The neutral compound exhibits multicolor bright phosphorescent emissions both in the solid state and in solution. The emission can be tuned to multiple visible colors by controlling the temperature, solvent, and {[3,5-(CF3)2Pz]Cu}3 concentration, giving rise to luminescence thermochromism, luminescence solvatochromism, and a new optical phenomenon called "concentration luminochromism", respectively.

Journal Article↗