Control of electronic and magnetic coupling via bridging ligand geometry in a bimetallic ytterbocene complex

The ligand 1-methyl-3,5-bis(2,2':6',2' '-terpyridin-4'-yl)benzene has been employed in the synthesis of a new bimetallic ytterbocene complex [(Cp*)2Yb](1-methyl-3,5-bis(2,2':6',2' '-terpyridin-4'-yl)benzene)[Yb(Cp*)2] (1) and the doubly oxidized congener [1]2+ in an attempt to determine the impact of the bridging ligand geometry on the magnetic/electronic properties as compared to the previously reported 1,4-analog [(Cp*)2Yb](1,4-di(terpyridyl)benzene)[Yb(Cp*)2] (2). Electrochemical, electronic, and magnetic data provide compelling evidence that the 1,3-geometry associated with the bridging ligand of 1 has done an effective job of inhibiting electronic communication between metal centers and magnetic coupling of spin carriers at room temperature as compared to 2. In fact, the physical data associated with 1 are quite similar to those reported for the monometallic analog (Cp*)2Yb(tpy) (3). In particular, the f-f profile of [1]2+ is nearly identical to that of [3]+ in its spectral features but with an almost exact doubling of the intensities. Further, the electronic coupling between metal centers as manifested in the potential separation between metal-based reduction waves has for the first time in these bimetallic ytterbocene complexes been found to go to zero for 1. Thus, the linkage isomerism at the phenyl coupling unit has induced a change in the ground-state electronic configuration from the singlet dianion-bridged (4f)13(pi*)2(4f)13 state found in 2 to the diradical-bridged (4f)13(piA*)1(piB*)1(4f)13 state in 1. This diradical formulation on the bridging ligand in 1 is supported by DFT calculations for the uncomplexed doubly reduced ligand that indicate the ground-state configuration is a singlet diradical state with the triplet-diradical state lying to slightly higher energy. Magnetic characterization of 1 is most consistent with the behavior previously observed for monometallic analogs such as 3, and there is no evidence of long-range magnetic ordering such as that observed for 2. In addition, X-ray crystallographic characterization of 1 represents the first case of a structurally characterized 2:1 metal-to-ligand adduct of the 1,3-bis(tpy) framework.     

A novel dithioferrocenophane with a vic-dioxine moiety in the bridging chain

The amphi and anti isomers of 1,4-dithia-2,3-bis(hydroxyimino)[4](1,1′)ferrocenophane were prepared by the reaction of disodium 1,1′-ferrocenedithiolate with anti-dichloroglyoxime. The Ni^II complex of the amphi isomer was also isolated and characterized.     

New type of ruthenium sensitizers with a triazole moiety as a bridging group

A new type of ruthenium sensitizers JK-91 and JK-92 with a triazole moiety as a bridging group were designed and synthesized in an attempt to increase the π-conjugated system. Two compounds work as highly efficient sensitizers for the dye-sensitized nanocrystalline TiO₂ solar cell. Under standard AM 1.5 sunlight, the sensitizer JK-91 yielded a short-circuit photocurrent density of 12.55 mA/cm², an open-circuit voltage of 0.73 V, and a fill factor of 0.73, corresponding to an overall conversion efficiency of 6.75%.     

A 2-D bimetallic assembly with bridging cyanide ions

A novel cyanide-bridged bimetallic assembly, [Cu(1,3-Pn)₂]₂[Fe^III(CN)₆]ClO₄ · 2H₂O (1,3-Pn = 1,3-diaminopropane), derived from [Fe(CN)₆]^3– building blocks and four-coordinated bisdiamine metal(II) ions [Cu(1,3-Pn)₂]²⁺ is described and characterized by X-ray crystal analysis. The compound contains a two-dimensional network structure extended through Fe^III—CN—Cu linkages. Mössbauer experimental results indicate that the iron is ferric (Fe³⁺) in the complex. Cryomagnetic measurements reveal an antiferromagnetic exchange interaction between the nearest paramagnetic metal ions in the compound. The exchange mechanism was also discussed.     

Synthesis, structure, and magnetism of bimetallic manganese or nickel complexes of a bridging verdazyl radical

Two binuclear metal-radical complexes, formed by the reaction of M(hfac)(2) x 2H(2)O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)(2)](2)) crystallizes in the monoclinic space group C2/c: C(30)H(17)N(6)O(9)F(24)Mn(2), a = 29.947(3), b = 17.143(3), c = 16.276(3) A, beta = 123.748(3)*, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = -48 cm(-1)). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm(-1)). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species.     

Reaction of carbon dioxide with a bimetallic octadienylbridged palladium complex

Reaction of equimolar amounts of μ-1–3-η:6–8-η-octadienatobis(1,1,1,5,5,5-hexafluoroacetylacetonatopalladium) and triisopropylphosphine gives a bimetallic octadienyl-bridged complex, in which one palladium atom is η¹ -bound to the terminal carbon of the octadienyl chain. Insertion of CO₂ into this PdC bond gives a carboxylate complex; acidic decomposition and hydrogenation of the carboxylate complex gives pelargonic acid. The results are discussed in relation to the mechanism of the palladium-catalyzed reaction between butadiene and carbon dioxide.     

Rhodium(I) diolefin complexes with polycyclic π-arene ligands. Synthesis of bimetallic complexes with diphenylmethane as bridging ligand

Summary The preparation and properties of cationic arenerhodium(I) complexes of general formula [Rh(diolefin)(⁶arene)]ClO₄ (diolefin=1,5-cyclooctadiene, tetrafluorobenzobarrelene or trimethyltetrafluorobenzobarrelene; arene = biphenyl or diphenylmethane) are described. These complexes react with the solvated intermediate complex [Rh(diolefin)(Me₂CO)_x]ClO₄ to give homobimetallic [(diolefin)Rh(Ph₂CH₂)Rh(diolefin)](ClO₄)₂ derivatives. New heterobimetallic complexes of the type [(diolefin)Rh(Ph₂CH₂)Cr(CO)₃]ClO₄ have been synthesized by reaction of Cr(CO)₃(⁶-Ph₂CH₂) with the solvated complex [Rh(diolefin)(Me₂CO)_x]ClO₄ or, alternatively by treatment of [Rh(diolefin)(⁶-arene)]ClO₄ with the complex Cr(CO)₃(⁶Me₃B₃N₃Me₃) in chloroform solution.     

Synthesis of new trifluoromethyl peptidomimetics with a triazole moiety

gem-Chloroamine CF₃CH(Cl)NHAc 1 reacts in a one-pot sequence with NaN₃ to afford trifluoromethyl azido compound 2 and further undergoes a Huisgen 1,3-dipolar cycloaddition with alkynes to yield 1,4-disubstitued 1,2,3-triazoles. The reaction is catalyzed by Cu(II) species (Cu(OAc)₂, 10 mol %) without any reducing agent, and the corresponding products are afforded in high yields (74-87%). This process offers thus an entry to new trifluoromethyl pseudopeptides.     

Synthesis and structure of new dinuclear palladium complex containing no bridging ligands

Oxidation of the mononuclear semiquinonediimine complex [(NPh)(NH)C₆H₄]₂Pd with silver trifluoromethanesulfonate afforded the diamagnetic dinuclear dicationic palladium complex {[(NPh)(NH)C₆H₄]₂Pd}₂(O₃SCF₃)₂ with a Pd...Pd distance of 3.267(1) . The complex was structurally characterized, and its spectroscopic and electrochemical properties were studied.     

A bimetallic complex containing a cyclopentadienyl-annulated imidazol-2-ylidene

A bimetallic carbene complex architecture that incorporates a cyclopentadienyl-annulated imidazol-2-ylidene moiety is characterized. The ligand architecture enables direct electronic interaction between the pi- and sigma-bonded metals. A preliminary example of aqueous Suzuki coupling employing a metallocene-fused imidazol-2-ylidene-derived catalyst is described.     

Synthesis of pyrimidinocyclophanes having a bridging nitrogen atom

Reactions of 1,3-bis(ω-bromoalkyl)-substituted uracils, quinazoline-2,4-dione, and 5-methyl-1,3,5-triazine-2,4,6-trione and 1,3-bis(m-bromomethylbenzyl)-5-bromouracil with amines (aliphatic amines, benzylamines, naphthylmethanamine, and anisidine) gave a series of macrocyclic compounds having one pyrimidine or triazine fragment and an azapolymethylene bridge connecting the N¹ and N³ atoms of the heteroring. The bridging nitrogen atom in some macrocyclic compounds was subjected to quaternization with methyl p-toluenesulfonate.     

A diketiminate‐bound diiron complex with a bridging carbonate ligand

Reduction of carbon dioxide by a diiron(I) complex gives μ‐carbonato‐κ³O:O′,O′′‐bis{[2,2,6,6‐tetramethyl‐3,5‐bis(2,4,6‐triisopropylphenyl)heptane‐2,5‐diiminate(1−)‐κ²N,N′]iron(II)} toluene disolvate, [Fe₂(C₄₁H₆₅N)₂(CO₃)]·2C₇H₈, a diiron(II) species with a bridging carbonate ligand. The asymmetric unit contains one diiron complex and two cocrystallized toluene solvent molecules that are distributed over three sites, one with atoms in general positions and two in crystallographic sites. Both Fe^II atoms are η²‐coordinated to diketiminate ligands, but η¹‐ and η²‐coordinated to the bridging carbonate ligand. Thus, one Fe^II center is three‐coordinate and the other is four‐coordinate. The bridging carbonate ligand is nearly perpendicular to the iron–diketiminate plane of the four‐coordinate Fe^II center and parallel to the plane of the three‐coordinate Fe^II center.     

Stacking interaction in crystals of a dinuclear rhodium complex with a bridging phenylborole ligand

Russian Chemical Bulletin -     

Synthesis of steroid compounds containing a pyridazinone moiety

Russian Chemical Bulletin - The reaction of 17-ketosteroids and glyoxylic acid followed by treatment with hydrazine affords steroid compounds condensed in the 16 and 17 positions with the...     

A binuclear tantalum(III) complex with a bridging carboxylato ligand

Ta₂Cl₆(SMe₂)₃ reacts with one equivalent of C₄H₉CO₂Li to give a complex with a bridging carboxylate ligand, Ta₂Cl₅(O₂CC₄H₉)(SMe₂)(THF)₂. The product was isolated in two crystalline forms, 1 and 2, from a THF/hexane and benzene/hexane solvent mixture, respectively. The following are the unit cell parameters, for 1: monoclinic (P2₁/n), a = 10.537(5) Å, b = 22.015(4) Å, c = 11.663(4) Å, β = 107.80(3)°, V = 2576(3) ų, and Z = 4; for 2: monoclinic (P2₁/c), a = 15.584(4) Å, b = 15.647(4) Å, c = 11.275(3) Å, β = 106.04(5)°, V = 2642(3) ų and Z = 4. The complex is a dimer with a distorted octahedra-sharing-an-edge geometry. The TaTa distances in 1 and 2 were 2.766(1) Å and 2.779(1) Å, respectively, which is somewhat longer than in previously reported Nb(III) and Ta(III) dinuclear compounds. Diamagnetism of the complex is shown by NMR. Fenske—Hall calculations, which correctly predict an electronic transition at about 16,000 cm^?1, indicate a double TaTa bond. The observed elongation of the metalmetal bond is attributed mainly to steric crowding. The complex is the first proven low-valent Ta species with a coordinated carboxylate ion.     

Synthesis,characterization and crystal structure analysis of a novel oxo-centered mixed-metal complex containing unsaturated bridging carboxylates

A novel oxo-centered trinuclear mixed-metal carboxylate complex with unsaturated bridging ligands [Fe₂Cr(μ₃-O)(C₃H₃O₂)₆(H₂O)₃]·NO₃·4H₂O has been synthesized and characterized by means of Elemental analyses, Infrared spectroscopy and Crystal structure analysis. The compound crystallizes isotypically in the monoclinic space group type P2₁/c. In the compound, each M^(III) cation is coordinated by six O atoms from four unsaturated carboxylate groups as bridging ligands, one water molecule as the terminal ligand, and a μ₃-oxygen atom in the center of an equilateral triangle. The infrared spectra show resolved bands arising from ν_asym(COO) and ν_sym(COO) vibration of bridging carboxylate ligands along with those of ν_asym(M₂M′O) vibration in the complex. The difference between symmetrical and asymmetrical (COO) ligands indicate that the acrylate bridge is present in the structure of complex.      

Synthesis,crystal structure and magnetic behavior of a two-dimensional copper(II) complex with mellitic anion as bridging ligand

A two-dimensional complex Cu₃[C₆(COO)₆](H₂O)₁₀ · 2H₂O has been prepared and its crystal structure determined by X-ray crystallography. In the complex each mellitic anion provides four carboxylate groups as coordinate groups and, according to the coordination, the four carboxylate groups are classified as two types according to its coordinate modes. The first is that a carboxylate group coordinates a copper(II) ion via its one oxygen atom, and the second one is that a carboxylate group, as a two-dentate ligand, coordinates to two copper(II) ions. The copper(II) ions also are classified as being of two types according to their coordinate modes. The configuration around each copper(II) ion is a distorted pyramid. The variable-temperature magnetic susceptibility of the complex was measured in the 4–300 K range and the magnetic data indicate that the magnetic interaction between bridging copper(II) ions displays an antiferromagnetic coupling below 42 K, while above 42 K a ferromagnetic interaction appears.