Niranjan Goswami

Structure, NMR and other physical and photophysical properties of ruthenium(II) complexes containing the 3,3′-dicarboxyl-2,2′-bipyridine ligand

Abstract A series of compounds of the type [(bpy) 2 Ru(3,3′-XX-2,2′-bpy)] 2+ or [(dmb) 2 Ru(3,3′-XX-2,2′-bpy)] 2+ , where X is CH 2 OH, COOH, COOCH 3 , COOC 2 H 5 , and COOCH 2 C 6 H 5 and bpy and dmb are 2,2′-bipyridine and 4,4′-dimethyl-2,2′-bipyridine, respectively, have been synthesized. [Ru(bpy) 2 ((COOCH 3 ) 2 bpy)](PF 6 ) 2 ·2CH 3 CN crystallized in the monoclinic space group P 2 1 / c with a =15.347 (3), b =22.767 (4), c =12.971 (3) A, and Z =4. 1 H-NMR spectra were assigned. The proton on the carbon atom neighboring the nitrogen coordination site shifts upfield upon coordination to ruthenium(II). Electronic absorptions occur over the visible region from 550 to 400 nm, which are attributed to metal-to-ligand charge transfer and in the UV region from 250 to 350 nm, which are associated with intraligand processes. The absorbance in the visible region of the spectrum displays two components, Ru(dπ)→π*(bpy) and Ru(dπ)→π*((COOR) 2 bpy) for R=CH 3 , C 2 H 5 and CH 2 C 6 H 5 , in the other cases the Ru(dπ)→π* transitions to the three bipyridine ligands overlap. Reduction potentials attributed to the Ru(III/II) couple range from 1.22 V for the CH 2 OH derivative to 1.40 V versus SSCE for the COOC 2 H 5 derivative. Reductions attributed to the first reduction of the coordinated (3,3′-XX-2,2′-bpy) ligand occur over the range −0.88 to −1.36 V versus SSCE. Emission maxima at room temperature in acetonitrile range from 614 nm for the CH 2 OH derivative to 711 nm for the ester derivatives; their emission lifetimes at room temperature in acetonitrile vary from 940 to 258 ns, respectively.

An Rh-105 complex of tetrathiacyclohexadecane diol with potential for formulating bifunctional chelates☆

1,5,9,13-Tetrathiacyclohexane-3,11-diol (16S4-diol), a sulfur crown ether analog, was studied as a potential chelating agent to complex no-carrier-added (NCA) grade 105Rh(III) in high yield at low ligand concentrations. trans-[RhCl2(16S4-diol)]chi (chi = Cl, PF6) was prepared using nonradioactive RhCl3.3H2O and characterized by UV-Vis, nuclear magnetic resonance (NMR) and X-ray crystallography. It was shown to have a +1 charge with the Rh(III) metal center coordinated to the four S atoms equatorially and two Cl atoms in trans axial positions. The 105Rh-16S4-diol complex prepared with NCA 105Rh(III)-chloride reagent was found to exhibit identical chromatographic properties as trans-[Rh(III)Cl2(16S4-diol)]+ (including silica and C-18 thin-layer chromatography [TLC] and electrophoresis). The preparation of 105Rh-16S4-diol complex formation optimized for conditions of pH, temperature, time, % ethanol and quantity of 16S4-diol resulted in yields > 90%. Very low quantities of 16S4-diol (3 nmol) complex NCA 105Rh(III) under relatively mild reaction conditions (heating at 64 degrees C for 90 min) in the presence of ethanol (10%), yielded the high specific activity 105Rh-16S4-diol complex as a single cationic species. The 105Rh-16S4-diol complex was shown to be stable for > or = 4 days in physiological buffers at room temperature and in human serum at 37 degrees C.

Crystal structure and physical properties of a ruthenium(II) bipyridine dimethylsulfoxide complex

The complex [Ru(bpy)2(DMSO)C1]PF6, where bpy is 2,2′-bipyridine and DMSO is dimethylsulfoxide, crystallizes in the triclinic space group P1¯ (#2) with a = 8.873 (2), b = 12.805 (4), c = 12.864 (4) Å, α = 97.76(3), β = 106.45(2), γ = 107.88(2); Z = 2, and dcalc = 1.75 mg/m3. The coordination geometry is that of a distorted octahedron with a cis −RuN4SCl arrangement of coordinating atoms. The four Ru—N distances to the bpy ligands are 2.082(5), 2.092(4), 2.044(4), and 2.078(5) Å. The Ru—Cl distance is 2.421(2) Å and the Ru—S distance to DMSO is 2.260(1) Å. The Ru—N bond distance trans to Cl is the shortest; the Ru—N bond distance trans to S is the longest. The complex is oxidized and reduced reversibly at 1.13 and −1.37 V vs. SSCE, respectively. It displays electronic absorptions at 515, 480 (1.5 × 104), 342 (1.5 × 104), 292 (1.2 × 105), and 240 nm (6.2 × 104) and has a broad emission band centered at 607 nm at 77 K in a 4:1 ethanol/methanol glass. The emission lifetime at room temperature is less than the pulse width of the laser, τ < 20 ns.

Rhodium-105 tetrathioether complexes: radiochemistry and initial biological evaluation

105Rhodium(III) complexes with three different acyclic tetrathioether ligands containing pendant carboxylic acid groups have been synthesized and characterized. The complexes were evaluated for stability under physiological conditions and the most promising complexes were evaluated in vivo in normal mice. The primary route of clearance for these complexes was the renal/urinary system, consistent with the presence of pendant carboxylate groups. The results indicate that the cis-[Rh(III)Cl2(2,5,8,11-tetrathiadodecane-1,12-dicarboxylic acid)]+ complex shows the most promising in vivo characteristics on which to base a potential therapeutic radiopharmaceutical.

Formation of an ethylene-bridged bis(benzisothiazole) dication by oxidative decomplexation of Ni(tsalen) with FeCl3

Abstract Treatment of Ni(tsalen), where H2tsalen = bis(thiosalicylidene)imine with FeCl3 results in the isolation of a crystalline compound with the composition [BBITE2+][Ni(tsalen)]4[FeCl4−]2 (I), where BBITE=1,2-bis(1,2-benzisothiazol-2-yl)ethane. The production of the BBITE2+ cation represents a 4-electron oxidation of the tsalen2− ligand, even though FeCl3 is not a strong enough oxidant to promote any outer-sphere oxidation of the Ni(tsalen) complex. The crystal structure of I shows a series of channels which are maintained by non-covalent interactions between the [Ni(tsalen)] and BBITE2+ molecules.

New Synthetic Techniques for Incorporation of Thiolate Donation in Transition Metal Complexes

A new method for the synthesis of metal complexes containing mixed nitrogen/sulfur coordination spheres is discussed. The use of 2,2′-dithiodibenzaldehyde as the source of the sulfur donors obviates the need for protection of the thiolate moiety. The reaction involves a concerted Schiff-base condensation and disulfide bond reduction. Mononuclear and dinuclear complexes of Ni(II), Cu(II), Fe(III), and Co(III) have been prepared by this method, including the first mononuclear Ni(II) complex of a non-porphyrinic tetradentate N3S ligand.