New insights into progressive ligand replacement from [Ru2Cl(O2CCH3)4]: synthetic strategies and variation in redox potentials and paramagnetic shifts.

The complete series of [Ru2Cl(Dp-FPhF)x(O2CCH3)4-x] (x = 1-4; Dp-FPhF- = N,N'-bis(4-fluorophenyl)formamidinate) compounds, has been prepared and characterized by a multi-technique approach, including single crystal X-ray diffraction. A careful study of the different methodologies has allowed us to prepare four compounds with good yields and without an inert atmosphere or further purification. Specifically, [Ru2Cl(Dp-FPhF)(O2CCH3)3] (1) was obtained using an ultrasound-assisted (USS) method, while [Ru2Cl(Dp-FPhF)4] (4) was prepared by microwave assisted solvothermal synthesis (MWS). The intermediate substitution products cis-[Ru2Cl(Dp-FPhF)2(O2CCH3)2] (2) and [Ru2Cl(Dp-FPhF)3(O2CCH3)] (3) have been prepared by conventional heating, controlling the molar ratio of the starting materials. ESI-MS and infrared spectroscopy were used to follow all the reactions and permitted a qualitative evaluation of the axial reactivity in this series. Magnetic and absorption measurements confirmed a high spin σ2π4δ2(π*δ*)3 electronic configuration in all cases. However, the effect of the gradual modification of the electronic density in the diruthenium core markedly affects other properties. The cyclic voltammograms of the compounds show a strong decrease in the one electron oxidation potential and an increase in the reduction potential in the series from 1 to 4. Furthermore, despite their paramagnetic nature, 1H- and 19F-NMR spectra were recorded, and a correlation between the paramagnetic shift of the signals and the substitution degree of the diruthenium species was observed. These results provide a comprehensive guide to synthesise and understand the effects of equatorial ligand substitution on the properties of Ru25+ compounds.

Heteronuclear Dirhodium-Gold Anionic Complexes: Polymeric Chains and Discrete Units.

In this article, we report on the synthesis and characterization of the tetracarboxylatodirhodium(II) complexes [Rh2(µ-O2CCH2OMe)4(THF)2] (1) and [Rh2(µ-O2CC6H4-p-CMe3)4(OH2)2] (2) by metathesis reaction of [Rh2(µ-O2CMe)4] with the corresponding ligand acting also as the reaction solvent. The reaction of the corresponding tetracarboxylato precursor, [Rh2(µ-O2CR)4], with PPh4[Au(CN)2] at room temperature, yielded the one-dimensional polymers (PPh4)n[Rh2(µ-O2CR)4Au(CN)2]n (R = Me (3), CH2OMe (4), CH2OEt (5)) and the non-polymeric compounds (PPh4)2{Rh2(µ-O2CR)4[Au(CN)2]2} (R = CMe3 (6), C6H4-p-CMe3 (7)). The structural characterization of 1, 3·2CH2Cl2, 4·3CH2Cl2, 5, 6, and 7·2OCMe2 is also provided with a detailed description of their crystal structures and intermolecular interactions. The polymeric compounds 3·2CH2Cl2, 4·3CH2Cl2, and 5 show wavy chains with Rh-Au-Rh and Rh-N-C angles in the ranges 177.18°-178.69° and 163.0°-170.4°, respectively. A comparative study with related rhodium-silver complexes previously reported indicates no significant influence of the gold or silver atoms in the solid-state arrangement of these kinds of complexes.

Synthesis and Structural Characterization of a Series of One-Dimensional Heteronuclear Dirhodium-Silver Coordination Polymers.

Herein, we describe the preparation of heteronuclear dirhodium-silver complexes by reaction between molecular Rh(II)-Rh(II) compounds [Rh2(µ-O2CR)4L2] (R = Me, Ph (1), CH2OEt (2); L = solvent molecules) with paddlewheel structure and PPh4[Ag(CN)2]. One-dimensional coordination polymers of (PPh4)n[Rh2(µ-O2CR)4Ag(CN)2]n (R = Me (3), Ph (4), CH2OEt (5)) formula have been obtained by replacement of the two labile molecules in the axial positions of the paddlewheel structures by a [Ag(CN)2]- bridging unit. The crystal structures of 3⁻5 display a similar arrangement, having anionic chains with a wavy structure and bulky (PPh4)⁺ cations placed between the chains. The presence of the (PPh4)⁺ cations hinders the existence of intermolecular Ag-Ag interactions although several C-H····π interactions have been observed. A similar reaction between [Rh2(µ-O2CCMe3)4(HO2CCMe3)2] and PPh4[Ag(CN)2] led to the molecular compound (PPh4)2{Rh2(µ-O2CCMe3)4[Ag(CN)2]2} (6) by replacement of the axial HO2CCMe3 ligands by two [Ag(CN)2]- units. The trimethylacetate ligand increases the solubility of the complex during the crystallization favouring the formation of discrete heteronuclear species.

Tetracarbonatodiruthenium Fragments and Lanthanide(III) Ions as Building Blocks to Construct 2D Coordination Polymers.

Two-dimensional coordination polymers of [Pr(DMSO)2(OH2)3][Ru2(CO3)4(DMSO)(OH2)]·5H2O (Prα) and [Ln(OH2)5][Ru2(CO3)4(DMSO)]·xH2O (Ln = Sm (Smß), Gd (Gdß)) formulae have been obtained by reaction of the corresponding Ln(NO3)3·6H2O dissolved in dimethyl sulphoxide (DMSO) and K3[Ru2(CO3)4]·4H2O dissolved in water. Some DMSO molecules are coordinated to the metal atoms reducing the possibilities of connection between the [Ru2(CO3)4]3- and Ln3+ building blocks giving rise to the formation of two-dimensional networks. The size of the Ln3+ ion and the synthetic method seem to have an important influence in the type of two-dimensional structure obtained. Slow diffusion of the reagents gives rise to Prα that forms a 2D net that is built by Ln3+ ions as triconnected nodes and two types of Ru25+ units as bi- and tetraconnected nodes with (2-c)(3-c)2(4-c) stoichiometry (α structure). An analogous synthetic procedure gives Smß and Gdß that display a grid-like structure, (2-c)2(4-c)2, formed by biconnected Ln3+ ions and two types of tetraconnected Ru25+ fragments (ß structure). The magnetic properties of these compounds are basically explained as the sum of the individual contributions of diruthenium and lanthanide species, although canted ferrimagnetism or weak ferromagnetism are observed at low temperature.

Polynuclear Iron(II) Complexes with 2,6-Bis(pyrazol-1-yl)pyridine-anthracene Ligands Exhibiting Highly Distorted High-Spin Centers.

Two bis-tridentate ligands L1 and L2 that contain 2,6-bis(pyrazol-1-yl) pyridine N-donor embraces introduced on a anthracene-acetylene backbone were used for the synthesis of a tetranuclear compound [Fe4(L1)4](CF3SO3)8·7CH3CN (1) and a hexanuclear compound [Fe6(L2)6](CF3SO3)12·18CH3NO2·9H2O (2). The polynuclear structures of both complexes were confirmed by X-ray diffraction studies, which revealed a [2 + 2] grid-like complex cation for 1 and a closed-ring hexagonal molecular architecture for the complex cation in 2. Although both compounds contain anthracene moieties arranged in a face-to-face manner, attempts at [4 + 4] photocyclization remain unsuccessful, which can be explained either by steric restraints or by inhibition of the photo-cycloaddition. Magnetic studies identified gradual and half-complete thermal spin crossover in the tetranuclear grid 1, where 50% of ferrous atoms exhibit thermal as well as photoinduced spin state switching and the remaining half of iron(II) centers are permanently blocked in their high-spin state. On the contrary, the hexanuclear compound 2 exhibits complete blocking in a high-spin state. Analysis of the magnetic data reveals the zero-field splitting parameter | D| ≈ 6-8 cm-1 with a large rhombicity for all high-spin iron(II) atoms in 1 or 2. The electronic structures and the magnetic anisotropies were also investigated by the multireference CASSCF/NEVPT2 method, and intramolecular exchange interactions were calculated by density functional theory methods.

Spin transition in arrays of gold nanoparticles and spin crossover molecules.

We investigate if the functionality of spin crossover molecules is preserved when they are assembled into an interfacial device structure. Specifically, we prepare and investigate gold nanoparticle arrays, into which room-temperature spin crossover molecules are introduced, more precisely, [Fe(AcS-BPP)2](ClO4)2, where AcS-BPP = (S)-(4-{[2,6-(dipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)ethanethioate (in short, Fe(S-BPP)2). We combine three complementary experiments to characterize the molecule-nanoparticle structure in detail. Temperature-dependent Raman measurements provide direct evidence for a (partial) spin transition in the Fe(S-BPP)2-based arrays. This transition is qualitatively confirmed by magnetization measurements. Finally, charge transport measurements on the Fe(S-BPP)2-gold nanoparticle devices reveal a minimum in device resistance versus temperature, R(T), curves around 260-290 K. This is in contrast to similar networks containing passive molecules only that show monotonically decreasing R(T) characteristics. Backed by density functional theory calculations on single molecular conductance values for both spin states, we propose to relate the resistance minimum in R(T) to a spin transition under the hypothesis that (1) the molecular resistance of the high spin state is larger than that of the low spin state and (2) transport in the array is governed by a percolation model.

Structural, magnetic and electrical properties of one-dimensional tetraamidatodiruthenium compounds.

The first bromo and iodo tetraamidatodiruthenium compounds of the type [Ru2X(µ-NHOCC6H4-R)4]n [X = Br, R = o-Me (1), m-Me (2), p-Me (3); X = I, R = o-Me (4), m-Me (5), p-Me (6)] have been prepared using solvothermal or microwave activation procedures. In these reactions ethanol or methanol as solvents have been used to make the synthesis procedures more environment-friendly. Solvothermal synthesis has allowed us to isolate single crystals of these extremely insoluble compounds and the crystal structures of all of them have been determined using single crystal X-ray diffraction. The change of the bridging halide ligand permits us to discuss the properties of these complexes on the basis of their structure. Complex 1 shows a Ru-Br-Ru angle of 180.0° whereas in complexes 2-6 the Ru-X-Ru angle varies from 110.16(2) to 115.39(4)°. In all compounds the ruthenium atom has a cis-RuN2O2 environment except in compound 1 that shows a positional disorder of N and O atoms. The bromide complex 1 shows a linear arrangement of the paddlewheel units in the resulting 1D coordination polymer. The fit of the magnetic data indicates that these compounds have non-negligible values of zero-field splitting with D values ranging from 41.10 to 60.10 cm(-1) and antiferromagnetic coupling constants from 0.00 to -4.13 cm(-1). Compound 1 is the first linear paddlewheel diruthenium compound that does not show a maximum in the representation of the magnetic susceptibility towards temperature. The electrical conductivity measurements in the temperature range 300-400 K of compounds 1, 4 and [Ru2Cl(µ-NHOCC6H4-o-Me)4]n (7) show that these compounds present semiconducting behaviours with conductivity values at 400 K in the range 0.3-3.0 × 10(-8) S cm(-1) for the Cl derivative (7), 7-18 × 10(-8) S cm(-1) for the Br derivative (1) and 27-68 × 10(-8) S cm(-1) for the I derivative (4) with average values of 1.4 × 10(-8), 13 × 10(-8) and 47 × 10(-8) S cm(-1), respectively.

Comparative study of different methods for the preparation of tetraamidato- and tetracarboxylatodiruthenium compounds. Structural and magnetic characterization.

Solvothermal and microwave assisted synthesis were used as green and very useful alternative methods to obtain new chloridotetraamidatodiruthenium compounds, [Ru(2)Cl(µ-NHOCR)(4)](n) [R = Me-o-C(6)H(4) (1), Me-m-C(6)H(4) (2), Me-p-C(6)H(4) (3)]. The analogous tetracarboxylato complexes [Ru(2)Cl(µ-O(2)CR)(4)](n) [R = Me-o-C(6)H(4) (4), Me-m-C(6)H(4) (5), Me-p-C(6)H(4) (6)] have also been obtained. These synthetic methods allow the use of greener solvents like water or ethanol. Moreover, solvothermal synthesis permits the direct crystallization of the desired complexes, which are extremely insoluble in common solvents, during the synthetic process. Therefore, the crystal structure of all of them has been established using single crystal X-ray diffraction. Complex 1 shows a Ru-Cl-Ru angle of 180° and constitutes the first example of a chloridotetraamidatodiruthenium derivative displaying linear chains in the solid state. In contrast, complexes 2·0.5EtOH, and 3-6 show polymeric arrangements with the diruthenium units linked by chloride ligands, forming zigzag chains with Ru-Cl-Ru angles ranging between 117.03(6) and 121.45(3)°. All of the complexes show magnetic moments at room temperature corresponding to three unpaired electrons in agreement with the σ(2)π(4)δ(2)(π*δ*)(3) ground-state configuration, which indicates a similar magnetic behaviour in amidato and carboxylato derivatives. In the linear arrangement of complex 1 there is a better magnetic communication between diruthenium units (antiferromagnetic coupling, zJ = -10.5 or -8.7 cm(-1)) than the one observed in the zigzag 2-6 complexes (zJ = -1.23 to -5.75 cm(-1)).

Tuning the spin-transition properties of pyrene-decorated 2,6-bispyrazolylpyridine based Fe(II) complexes.

Two 2,6-bispyrazolylpyridine ligands (bpp) were functionalized with pyrene moieties through linkers of different lengths. In the ligand 2,6-di(1H-pyrazol-1-yl)-4-(pyren-1-yl)pyridine (L1) the pyrene group is directly connected to the bpp moiety via a C-C single bond, while in the ligand 4-(2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)benzyl-4-(pyren-1-yl)butanoate (L2) it is separated by a benzyl ester group involving a flexible butanoic chain. Subsequent complexation of Fe(II) salts revealed dramatic the influence of the nature of the pyrene substitution on the spin-transition behaviour of the resulting complexes. Thus, compound [Fe(L1)(2)](ClO(4))(2) (1) is blocked in its high spin state due to constraints caused by a strong intermolecular π-π stacking in its structure. On the other hand, the flexible chain of ligand L2 in compounds [Fe(L2)(2)](ClO(4))(2) (2) and [Fe(L2)(2)](BF(4))(2)·CH(3)CN·H(2)O (3) prevents structural constraints allowing for reversible spin transitions. Temperature-dependent studies of the photophysical properties of compound 3 do not reveal any obvious correlation between the fluorescence of the pyrene group and the spin state of the spin transition core.

Nanostructures on surfaces of the metalorganic compound {Fe2(CO)6[µ-S2C6H2(OH)2]} and its potential as catalyst precursor for the synthesis of carbon nanotubes.

The compound {Fe(2)(CO)(6)[µ-S(2)C(6)H(2)(OH)(2)]} is organized by H-bond interactions on graphite and SiO(2) surfaces as micron-length nanofibres. Thermal degradation of these fibres adsorbed on SiO(2) leads to a very homogeneous surface filled with Fe(2)O(3) nanoparticles (ca. 2.5 nm diameter) suitable to produce few-walled carbon nanotubes laying on a clean surface.

Single layers of a multifunctional laminar Cu(I,II) coordination polymer.

A multifunctional bidimensional mixed-valence copper coordination polymer [Cu2Br(IN)2]n (IN = isonicotinato) has been characterized in crystal phase and isolated on graphite surface as single sheets.

S-S bond reactivity in metal-perthiocarboxylato compounds.

While M-percarboxylato species are elusive intermediates, their sulfur containing analogues are known in some cases. The feasibility of isolation of M-perthioacetato compounds allowed, in this work, to obtain new insights into the pathways that follow the reactivity of M-E-ER (E = O, S) fragments. Herein we report on the isolation of two new M-perthioacetato compounds: trans-[Pt(CH(3)CS(2)S)(2)] () and [Ni(CH(3)CSS)(CH(3)CS(2)S)] (), which have been fully characterized, including X-ray structures. Reactivity of these compounds towards PPh(3) has been studied combining UV-vis monitorization and NMR measurements. Overall the accumulated data suggest that the evolution of the perthioacetato ligand in complexes and by reaction with PPh(3) consists of a complex multistep pathway in which the sulfur transfer is preceded by electron transfer. Cyclic voltammetry measurements indicate that the transference of two electrons from the phosphorus to the sulfur atom is not concerted, suggesting that the first step of the reaction with PPh(3) is the monoelectronic electron transfer followed by P-S bond formation. The results presented here show a novel pathway in the field of S-S bond reactivity processes relevant in biological, synthetic systems and in hydrocarbon desulfurization processes.

Nanofibers generated by self-assembly on surfaces of bimetallic building blocks.

Adsorption on surfaces of diluted CH2Cl2 solutions of [Pt2(dta)4] (dta = dithioacetate) at room temperature does not lead to any organization. However, sonication or low temperature experiments results in the formation of 1D nanofibers on graphite.

Time-dependence structures of coordination network wires in solution.

We present a mechanochemistry-based procedure to isolate individual chains on surfaces of a ruthenium MMX polymer. After sonication of solutions containing the two building blocks of the mentioned MMX polymer, time-depending structures are formed in the solution. The architecture of the different structures obtained in this process, as a function of the time, is monitored using atomic force microscopy. The resulting structures exhibit uniform subnanometer diameters over microns length, in agreement with the expected diameter for an individual polymer chain. From the atomic force microscope images, we infer a long persistence length for the linear structures. Finally, the effect of the temperature solution in the formation of the different structures is also addressed.

MMX polymer chains on surfaces.

Fibres of [Ru(2)Br(micro-O(2)CEt)4]n polymer have been isolated on different surfaces under specific conditions, and morphologically characterised by AFM and STM, showing an unexpected helical internal structure.

Discrete and monodimensional heteropolynuclear structures formed by tetracarboxylatodiruthenium(II,III) and perrhenato fragments.

Reaction between cationic units of carboxylate-bridged diruthenium complexes [Ru(2)(mu-O(2)CR)(4)](+) (R = Me, CMePh(2), CMe(3), CH(2)CH(2)OMe, C(Me)=CHEt, C(6)H(4)-p-OMe, Ph) and tetrabutylammonium perrhenate gives complexes with different arrangements in the solid state. Thus, the compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)) [R = Me (1), CMePh(2) (2), CMe(3) (3), CH(2)CH(2)OMe (4), C(Me)=CHEt (5), C(6)H(4)-p-OMe (6), Ph (7)] have polymeric structures with the diruthenium units linked by perrhenate ligands in the axial positions. The structures of complexes 3.THF and 4 were established by single-crystal X-ray diffraction. The tetrahedral geometry of the ReO(4)(-) anion permits the formation of a chain close to the linearity. In contrast to the polymeric chains observed in complexes 1-7, the reaction of [Ru(2)(mu-O(2)CPh)(4)](+) with NBu(4)ReO(4) also affords the compounds Ru(2)(mu-O(2)CPh)(4)(ReO(4))(H(2)O) (8) and NBu(4)[Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)] (9) depending on the reaction conditions. The structure of 8 consists of cationic and anionic units, [Ru(2)(mu-O(2)CPh)(4)(H(2)O)(2)](+) and [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-), linked by hydrogen bonds, which give a three-dimensional net. The structure of complex 9.0.5H(2)O has an anionic unit similar to that of 8, whose counterion is NBu(4)(+). The Ru-Ru bond distances are slightly longer in [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-) than in the polymeric compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)). The magnetic behavior owes to the existence of zero-field splitting (ZFS) and a weak antiferromagnetic coupling. The experimental data are fitted with a model that considers the ZFS effect using the Hamiltonian (D) = SDS. The weak antiferromagnetic coupling is introduced as a perturbation, using the molecular field approximation.