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.

Bidirectional noninnocence of hinge-like deprotonated bis-lawsone on selective ruthenium platform: a function of varying ancillary ligands.

The present work aimed to obtain discrete heavier metal complexes of unperturbed deprotonated bis-lawsone (hinge-like H2L = 2,2'-bis(3-hydroxy-1,4-napthoquinone). This is primarily due to its limited examples with lighter metal ions (Co, Zn, and Ga) and the fact that our earlier approach with the osmium ion facilitated its functionalisation. Herein, we demonstrated the successful synthesis and structural characterisation of L2--derived diruthenium [(bpy)2RuII(µ-L2-)RuII(bpy)2](ClO4)2 [1](ClO4)2 (S = 0), (acac)2RuIII(µ-L2-)RuIII(acac)22 (S = 1) and monoruthenium (pap)2Ru(L2-) 3 (S = 0) derivatives (bpy = 2,2'-bipyridine, acac = acetylacetonate, and pap = 2-phenylazopyridine). The crystal structures established that (i) O,O-/O,O- donating five-membered bis-bidentate and O-,O- donating seven-membered bidentate chelating modes of deprotonated L2- in rac (ΔΔ/ΛΛ) diastereomeric [1](ClO4)2, 2 and 3, respectively. (ii) The L2- bridging unit in [1](ClO4)2, 2 and 3 underwent twisting its two naphthoquinone rings with respect to the ring connecting C-C bond by 73.01°, 62.15° and 59.12°, respectively. (iii) Intermolecular π-π interactions (∼3.5 Å) between the neighbouring molecules. The paramagnetic complex 2 (S = 1) with two non-interacting Ru(III) (S = 1/2) ions exhibited weak antiferromagnetic coupling only at very low temperatures. In agreement with the magnetic results, 2 displayed typical RuIII-based anisotropic EPR in CH3CN (/Δg: 2.314/0.564) but without any forbidden g1/2 signal at 120 K. The complexes exhibited multiple redox processes in CH3CN in the experimental potential window of ± 2.0 V versus SCE. The analysis of the redox steps via a combined experimental and theoretical (DFT/TD-DFT) approach revealed the involvement of L2- to varying extents in both the oxidative and reductive processes as a consequence of its bidirectional redox non-innocent feature. The mixing of the frontier orbitals of the metal ion and L2- due to their closeness in energy indeed led to the resonating electronic form in certain redox states instead of any precise electronic structural state.

Ultrasound-assisted synthesis of water-soluble monosubstituted diruthenium compounds.

The elusive monosubstituted diruthenium complexes [Ru2Cl(DAniF)(O2CMe)3] (1), [Ru2Cl(DPhF)(O2CMe)3] (2), [Ru2Cl(D-p-CNPhF)(O2CMe)3] (3), [Ru2Cl(D-o-TolF)(O2CMe)3] (4), [Ru2Cl(D-m-TolF)(O2CMe)3] (5), [Ru2Cl(D-p-TolF)(O2CMe)3] (6) and [Ru2Cl(p-TolA)(O2CMe)3] (7) have been synthesized using for the first time ultrasound-assisted synthesis to carry out a substitution reaction in metal-metal bonded dinuclear compounds (DAniF- = N,N'-bis(4-anisyl)formamidinate; DPhF- = N,N'-diphenylformamidinate; D-p-CNPhF- = N,N'-bis(4-cyanophenyl)formamidinate; D-o/m/p-TolF- = N,N'-bis(2/3/4-tolyl)formamidinate; p-TolA- = N-4-tolylamidate). This is a simpler and greener method than the tedious procedures described in the literature, and it has permitted to obtain water-soluble complexes with good yields in a short period of time. A synthetic study has been implemented to find the best experimental conditions to prepare compounds 1-7. Two different types of ligands, formamidinate and amidate, have been used to check the generality of the method for the preparation of monosubstituted complexes. Five new compounds (2-6) have been obtained using a formamidinate ligand, the synthesis of the previously described compound 1 has been improved, and an unprecedented monoamidate complex has been achieved (7). The crystal structures of compounds 3 and 7 have been solved by single crystal X-ray diffraction. These compounds show the typical paddlewheel structure with three acetate ligands and one formamidinate (3) or amidate (7) bridging ligand at the equatorial positions. The axial positions are occupied by the chloride ligand giving rise to one-dimensional polymer structures that were previously unknown for monosubstituted 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.

Three Bis-BODIPY Analogous Diruthenium Redox Series: Characterization and Electronic Structure Analysis.

The dianion derived from (2Z,6Z)-3,7-diphenyl-N2,N6-di(pyridin-2-yl)pyrrolo[2,3-f]indole-2,6(1H,5H)-diimine (H2 BL), a modified BODIPY ligand precursor, is shown to be capable of bridging two metal complex fragments RuL2 , L=2,4-pentanedionato (acac- ), 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap) in [Ru(acac)2 Ru(µ-BL)Ru(acac)2 ] (1/2), [Ru(bpy)2 Ru(µ-BL)Ru(bpy)2 ](ClO4 )2 ([3](ClO4 )2 ) and [Ru(pap)2 Ru(µ-BL)Ru(pap)2 ](ClO4 )2 ([4](ClO4 )2 ). The compounds, including a diastereoisomeric pair 1 (meso) and 2 (rac) were spectroscopically and structurally characterized. Reversible electron transfers as revealed by cyclic and differential pulse voltammetry allowed for an EPR and UV-vis-NIR spectroelectrochemical investigation of several neighboring charge states. Together with susceptibility measurements and TD-DFT calculations the assignment of oxidation states reveals that 1, 2 are diruthenium(III) species which can be oxidized or reduced by one electron whereas 32+ and 42+ contain ruthenium(II) and get reduced or oxidized mainly at the dianionic bridge (32+ ) or are reduced at the ancillary ligands pap (42+ ).

pH- and Time-Dependent Release of Phytohormones from Diruthenium Complexes.

The controlled release of functionally active compounds is important in a variety of applications. Here, we have synthesized, characterized, and studied the magnetic properties of three novel metal-metal-bonded tris(formamidinato) Ru25+ complexes. We have used different auxin-related hormones, indole-3-acetate (IAA), 2,4-dichlorophenoxyacetate (2,4-D), and 1-naphthaleneacetate (NAA), to generate [Ru2Cl(µ-DPhF)3(µ-IAA)] (RuIAA), [Ru2Cl(µ-DPhF)3(µ-2,4-D)] (Ru2,4-D), and [Ru2Cl(µ-DPhF)3(µ-NAA)] (RuNAA) (DPhF = N,N'-diphenylformamidinate). The crystal structures of RuIAA, RuIAA·THF, Ru2,4-D·CH2Cl2, and RuNAA·0.5THF have been determined by single-crystal X-ray diffraction. To assess the releasing capacity of the bound hormone, we have employed a biological assay that relied on Arabidopsis thaliana plants expressing an auxin reporter gene and we demonstrate that the release of the phytohormones from RuIAA, Ru2,4-D, and RuNAA is pH- and time-dependent. These studies serve as a proof of concept showing the potential of these types of compounds as biological molecule carriers.

Preparation of Dimeric Monopentamethylcyclopentadienyltitanium(III) Dihalides and Related Derivatives.

The synthesis, crystal structure, and reactivity of a series of half-sandwich titanium(III) dihalide complexes [Ti(η5-C5Me5)X2] (X = Cl, Br, I) and several of its Lewis base derivatives were investigated. The reaction of the trihalides [Ti(η5-C5Me5)X3] (X = Cl (1), Br (2), I (3)) with LiAlH4 (≥1 equiv) in toluene at room temperature results in the formation of the halide-bridged dimers [{Ti(η5-C5Me5)X(µ-X)}2] (X = Cl (4), Br (5), I (6)). The treatment of 4 with [Li{N(SiMe3)2}] (≥2 equiv) at room temperature affords the precipitation of the amido titanium(III) complex [{Ti(η5-C5Me5)(µ-Cl){N(SiMe3)2}}2] (7), but analogous reactions of 4 with other lithium reagents [LiR] (R = Me, CH2SiMe3, NMe2) lead to disproportionation into titanium(IV) [Ti(η5-C5Me5)R3] and presumably titanium(II) derivatives. Similarly, complex 4 in solution at temperatures higher than 100 °C undergoes disproportionation as demonstrated by its reactions with cobaltocene and N-(4-methylbenzylidene)aniline yielding the ionic paramagnetic compound [Co(η5-C5H5)2][Ti(η5-C5Me5)Cl3] (8) and the diamagnetic diazatitanacyclopentane [Ti(η5-C5Me5)Cl{N(Ph)CH(p-tolyl)}2], respectively. Treatment of complex 4 with 2 equiv of 2,6-dimethylphenylisocyanide or tert-butylisocyanide in toluene at room temperature affords the paramagnetic titanium(III) dinuclear adducts [{Ti(η5-C5Me5)Cl(µ-Cl)(CNR)}2] (R = 2,6-Me2C6H3 (9), tBu (10)). Magnetic studies for polycrystalline 9 show that it displays a weak intramolecular antiferromagnetic coupling between the Ti ions, which is consistent with the long Ti-Ti distance of 3.857(1) Å determined by X-ray diffraction. The isocyanide ligands in complex 10 undergo a reductive coupling reaction in toluene to give the titanium(IV) iminoacyl derivative [{Ti(η5-C5Me5)Cl2}2(µ-η2:η2-tBuN═C-C═NtBu)] (11). Whereas an analogous dinuclear structure was found in the aqua titanium(III) complex [{Ti(η5-C5Me5)Cl(µ-Cl)(OH2)}2] (12), resulting from the reaction of 4 with adventitious amounts of water, compound 4 reacts with excess ammonia to give a mononuclear adduct [Ti(η5-C5Me5)Cl2(NH3)2] (13) with a robust layered pattern in the solid state.

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.

Questions of Noninnocence and Ease of Azo Reduction in Diruthenium Frameworks with a 1,8-Bis(( E)-phenyldiazenyl)naphthalene-2,7-dioxido Bridge.

Ligands containing the azo group are often used in various metal complexes owing to their facile one-electron reduction, which in effect extends the means of degrading environmentally harmful azo dyes. In order to probe the idea of the generally accepted ease of reduction of azo-containing compounds, we present here three different diruthenium complexes [(acac)2RuIII(µ-L2-)RuIII(acac)2] (diastereomeric 1/2), [(bpy)2RuII(µ-L2-)RuII(bpy)2](ClO4)2 ([3](ClO4)2), and [(pap)2RuII(µ-L2-)RuII(pap)2](ClO4)2 ([4](ClO4)2 ) with a bridging ligand (L2- = 1,8-bis(( E)-phenyldiazenyl)naphthalene-2,7-dioxido) that contains azo groups in addition to phenoxide-type donors. The RuIII-RuIII complexes (1/2) display interesting one-dimensional-chain effects, as revealed by temperature-dependent magnetic studies. The stability of the RuIII oxidation state in 1/2 under ambient conditions correlates well with the σ-donating acetylacetonato (acac) coligands. However, with π-accepting 2,2/-bipyridine (bpy) or phenylazopyridine (pap) the RuII state is preferably stabilized in 32+ or 42+, respectively, but there are interesting differences in their oxidative chemistry. The moderately π accepting bpy allows for the RuII to RuIII oxidation at reasonably low anodic potentials. However, for the strongly π accepting pap, no RuII to RuIII oxidation is observed within the solvent window. Instead, a phenoxide to phenoxyl radical type of oxidation based on the bridging ligand is observed. Surprisingly, the reductive chemistry of all three complexes is dominated by either the ruthenium centers or the coligands (bpy or pap), with no reductions observed on the azo function associated with the central bridging ligand (L2-). All of the above conclusions were drawn from combined structural, electrochemical, magnetic, spectroelectrochemical, and DFT investigations. Our results thus conclusively establish that the ease of reduction of an azo group in a particular compound is critically dependent on its substituents and that the noninnocence of the bridging ligands (L2-) in the dinuclear complexes can be decisively tuned by the appropriate choice of ancillary ligands.

Coordination capacity of cytosine, adenine and derivatives towards open-paddlewheel diruthenium compounds.

[Ru2Cl2(DPhF)3] (DPhF = diphenylformamidinate) links preferentially to the junctions of RNA (ribonucleic acid) structures, although the bonding mode is not known. In order to clarify this question the reactions between [Ru2Cl2(DPhF)3] and cytosine (Hcyto), cytidine (Hcyti), cytidine 2',3'-cyclic monophosphate sodium salt (NacCMP), adenine (Hade), adenosine (Haden) and adenosine 3',5'-cyclic monophosphate (HcAMP) have been carried out. In the resultant complexes, cyto (cytosinate), cyti (cytidinate), cCMP (cytidine 2',3'-cyclic monophosphate monoanion), ade (adeninate), aden (adenosinate) and cAMP (deprotonated adenosine 3',5'-cyclic monophosphate) are bonded to the diruthenium unit as N,N'-bridging ligands, as confirmed by the solution of the crystal structures of [RuCl(DPhF)3(cyto)] and [RuCl(DPhF)3(ade)] by X-ray diffraction. The axial positions of the diruthenium species are still available for additional interactions with other residues that could explain its preference towards RNA junctions.

Unsymmetric (µ-oxido)/(µ-pyrazolato) and Symmetric (µ-pyrazolato)2 Bridged Diosmium Frameworks: Electronic Structure and Magnetic Properties.

The present article deals with the structurally characterized unsymmetric oxido/pyrazolato-bridged [(bpy)2Os(III)(µ-oxido)(µ-pz)Os(III)(bpy)2](ClO4)3 ([1](ClO4)3) and symmetric dipyrazolato-bridged [(bpy)2Os(II)(µ-pz)2Os(II)(bpy)2](ClO4)2 ([2](ClO4)2) (pz = pyrazolato, bpy = 2,2'-bipyridine) complexes with the Os···Os separations of 3.484 and 4.172 Å, respectively. The anti-ferromagnetically coupled Os(III) centers [E(S = 1)-E(BS(1,1) S = 0) = 322.504 cm(-1)] in 1(3+) and diamagnetic (S = 0) 2(2+) exhibit well-resolved (1)H NMR resonances. [1](ClO4)3 shows temperature- and magnetic field-dependent paramagnetism at low magnetic field and diamagnetism at high magnetic field. 1(3+) and 2(2+) display successive metal-based oxidation processes involving the intermediate mixed-valent states and isovalent congeners: Os(IV)Os(IV) (1(5+))→Os(III)Os(IV) (1(4+))⇌Os(III)Os(III) (1(3+))⇌Os(III)Os(II) (1(2+)) and Os(III)Os(III) (2(4+))→Os(II)Os(III) (2(3+))⇌Os(II)Os(II) (2(2+)) as well as bpy-centered reductions. The effect of π donor O(2-) and σ/π-donating pz(-) in 1(3+) and 2(2+), respectively, leads to varying oxidation state of the metal ions in the isolated complexes: Os(III)Os(III) versus Os(II)Os(II). UV-visible-near-IR-electron paramagnetic resonance spectro-electrochemistry and density functional theory (DFT)/time-dependent DFT calculations collectively reveal overlapping of the metal- and ligand (pz, O, bpy)-based frontier orbitals in the delocalized mixed-valent states in 1(4+) and 1(2+) with comproportionation constant (Kc) value > 1 × 10(14) as well as in isovalent 1(3+), resulting in mixed metal/ligand to metal/ligand near-IR transitions in all the three states. The mixed-valent Os(II)Os(III) state in 2(3+) exhibits high Kc value of 1 × 10(22) corresponding to a strong electrochemical coupling situation. However, closeness of the bandwidth (Δν1/2, 4861 cm(-1)) of broad and weak intervalence charge transfer transition of 2(3+) at 1360 nm (ε/M(-1) cm(-1): 490) with the calculated Δν1/2 of 4121 cm(-1) based on the Hush formula as well as spin-density distributions of Os1: 0.811/0.799, Os2: 0.045/0042, and pz: 0.162/0.173 in meso and rac diastereomeric forms, respectively, attribute its localized class II state.

Fingerprinting the junctions of RNA structure by an open-paddlewheel diruthenium compound.

RNA function is determined by its structural organization. The RNA structure consists of the combination of distinct secondary structure motifs connected by junctions that play an essential role in RNA folding. Selective 2'-hydroxyl acylation analyzed by primer extension (SHAPE) probing is an established methodology to analyze the secondary structure of long RNA molecules in solution, which provides accurate data about unpaired nucleotides. However, the residues located at the junctions of RNA structures usually remain undetected. Here we report an RNA probing method based on the use of a novel open-paddlewheel diruthenium (OPW-Ru) compound [Ru2Cl2(µ-DPhF)3(DMSO)] (DPhF = N,N'-diphenylformamidinate). This compound has four potential coordination sites in a singular disposition to establish covalent bonds with substrates. As a proof of concept, we have analyzed the reactivity of OPW-Ru toward RNA using two viral internal ribosome entry site (IRES) elements whose function depends on the structural organization of the molecule. Our study suggests that the compound OPW-Ru preferentially attacks at positions located one or two nucleotides away from junctions or bulges of the RNA structure. The OPW-Ru fingerprinting data differ from that obtained by other chemical reagents and provides new information about RNA structure features.

Metal-Induced Thiophene Ring Opening and C-C Bond Formation To Produce Unique Hexa-1,3,5-trienediyl-Coupled Non-Innocent Ligand Chelates.

Ring opening of thiophenes containing an azo function in 2-position and subsequent dimerization through C-C coupling were observed on reaction with [Ru(acac)2 (CH3 CN)2 ] (acac=acetylacetonate) to produce two 1,3,5-hexatriene-linked redox-active azothiocarbonyl chelate systems. Interaction of the non-innocent chelate ligands and of the metals at a nanoscale distance of 1.45 nm via the conjugated hexatriene bridge was studied by magnetic and electron spectroscopic measurements in conjunction with DFT calculations, revealing four-center magnetic interactions of this unique setting and weak intervalence coupling after reduction.

Formation of a novel ferromagnetic end-to-end cyanate bridged homochiral helical copper(II) Schiff base complex via spontaneous symmetry breaking.

A homochiral helical coordination polymer of copper(II) has been synthesized using achiral precursors via spontaneous symmetry breaking and has been confirmed by single crystal X-ray diffraction and solid-state CD spectroscopy. The variable temperature magnetic measurements indicate the presence of weak ferromagnetic exchange interactions mediated by end-to-end cyanate bridges (J = +0.12 cm(-1)).

Novel tetranuclear Ni(II) Schiff base complex containing Ni4O4 cubane core: synthesis, X-ray structure, spectra and magnetic properties.

Novel tetranuclear nickel(II) Schiff base complex having symmetric Ni4O4 cubane-core, [Ni4O2(OAc)2(L)2] (1) has been synthesized. Single crystal of the complex exhibits four nickel atoms in the alternate corner of the cubane and other four sites are occupied by phenolate-O and µ3-O(2-). Variable temperature magnetic moment data suggests the Ni centres are weakly antiferromagnetically coupled with J1=-4.82cm(-1) and J2=-4.83cm(-1). The electronic spectra, emission properties and life time measurement of ligand, HL and complex 1 have been studied.

Sensitivity of the valence structure in diruthenium complexes as a function of terminal and bridging ligands.

The compounds [(acac)2Ru(III)(µ-H2L(2-))Ru(III)(acac)2] (rac, 1, and meso, 1') and [(bpy)2Ru(II)(µ-H2L(•-))Ru(II)(bpy)2](ClO4)3 (meso, [2](ClO4)3) have been structurally, magnetically, spectroelectrochemically, and computationally characterized (acac(-) = acetylacetonate, bpy = 2,2'-bipyridine, and H4L = 1,4-diamino-9,10-anthraquinone). The N,O;N',O'-coordinated µ-H2L(n-) forms two ß-ketiminato-type chelate rings, and 1 or 1' are connected via NH···O hydrogen bridges in the crystals. 1 exhibits a complex magnetic behavior, while [2](ClO4)3 is a radical species with mixed ligand/metal-based spin. The combination of redox noninnocent bridge (H2L(0) → → → →H2L(4-)) and {(acac)2Ru(II)} → →{(acac)2Ru(IV)} or {(bpy)2Ru(II)} → {(bpy)2Ru(III)} in 1/1' or 2 generates alternatives regarding the oxidation state formulations for the accessible redox states (1(n) and 2(n)), which have been assessed by UV-vis-NIR, EPR, and DFT/TD-DFT calculations. The experimental and theoretical studies suggest variable mixing of the frontier orbitals of the metals and the bridge, leading to the following most appropriate oxidation state combinations: [(acac)2Ru(III)(µ-H2L(•-))Ru(III)(acac)2](+) (1(+)) → [(acac)2Ru(III)(µ-H2L(2-))Ru(III)(acac)2] (1) → [(acac)2Ru(III)(µ-H2L(•3-))Ru(III)(acac)2](-)/[(acac)2Ru(III)(µ-H2L(2-))Ru(II)(acac)2](-) (1(-)) → [(acac)2Ru(III)(µ-H2L(4-))Ru(III)(acac)2](2-)/[(acac)2Ru(II)(µ-H2L(2-))Ru(II)(acac)2](2-) (1(2-)) and [(bpy)2Ru(III)(µ-H2L(•-))Ru(II)(bpy)2](4+) (2(4+)) → [(bpy)2Ru(II)(µ-H2L(•-))Ru(II)(bpy)2](3+)/[(bpy)2Ru(II)(µ-H2L(2-))Ru(III)(bpy)2](3+) (2(3+)) → [(bpy)2Ru(II)(µ-H2L(2-))Ru(II)(bpy)2](2+) (2(2+)). The favoring of Ru(III) by σ-donating acac(-) and of Ru(II) by the π-accepting bpy coligands shifts the conceivable valence alternatives accordingly. Similarly, the introduction of the NH donor function in H2L(n) as compared to O causes a cathodic shift of redox potentials with corresponding consequences for the valence structure.

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.

Influence of ancillary ligands on the electronic structure and anion sensing features of ligand bridged diruthenium complexes.

The present article deals with a newer class of ligand bridged asymmetric complexes incorporating ancillary ligands (AL) with varying electronic characteristics: [(bpy)2Ru(II)(µ-HL(2-)) Ru(II)(bpy)2](ClO4)2·([1](ClO4)2); [(pap)2Ru(II)(µ-HL(2-))Ru(II)(pap)2](ClO4)2 ([2](ClO4)2); [(bpy)2Ru(II)(µ-HL(2-))Ru(II)(pap)2](ClO4)2 ([3](ClO4)2); [(acac)2Ru(III)(µ-HL(2-))Ru(III)(acac)2] (4) and [(bpy)2Ru(II)(µ-HL(2-))Ru(III)(acac)2]ClO4 ([5]ClO4) (H3L: 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid, bpy = moderately π-accepting 2,2'-bipyridine, pap = strongly π-accepting 2-phenylazopyridine, acac(-) = σ-donating acetylacetonate). The molecular identity of [1](ClO4)2 was established by its single crystal X-ray structure. A large shift in Ru(II)/Ru(III) potential of 0.7-2.0 V took place on switching the ancillary ligands from AL = bpy to pap to acac(-), leading to the stabilisation of ruthenium(II) and ruthenium(III) states in 1(2+), 2(2+), 3(2+), 4 and 5(+), respectively. The detailed magnetic studies revealed that the paramagnetic Ru(III)Ru(III) state in 4 essentially behaves as a system with two independent S = 1/2 spins and it exhibits an anisotropic EPR at 77 K ( = 2.192, Δg = g1-g3 = 0.70) but without any half-field signal near g∼ 4. The isolated mixed valent Ru(II)Ru(III) state in 5(+) exhibits weak antiferromagnetic coupling of -0.25 cm(-1) and anisotropic EPR with = 2.155, Δg = 0.704 but fails to show a Ru(II)→ Ru(III) IVCT (intervalence charge transfer) transition in the near-IR region up to 2000 nm. The complexes 1(2+), 2(2+) and 4 encompassing identical metal fragments, exhibited weak to moderate electrochemical coupling at the intermediate mixed valent states with Kc values of 10(2)-10(5). The coulometrically generated mixed valent Ru(II)Ru(III) state in 1(3+) or 4(-) also failed to display any prominent absorption in the near-IR region, but exhibited Ru(III) based rhombic EPR, implying valence localised situation with negligible intermetallic electronic coupling. The complexes 2(2+), 3(2+), 4 and 5(+) having one NH proton associated with the bridging ligand HL(2-) do not show any interaction with the anions F(-), Cl(-), Br(-), I(-), HSO4(-), H2PO4(-), OAc(-) and SCN(-) in CH3CN, though 1(2+) selectively recognises the fluoride ion.

Modulation of the magnetic properties of two-dimensional compounds [NiX2(N-N)] by tailoring their crystal structure.

A series of 2-D nickel compounds with the stoichiometry [NiCl2(N-N)] has been prepared, [N-N = pyrazine (1), 4,4'-bipyridine (2), trans-4,4'-azopyridine (3), trans-1,2-bis(4-pyridyl)ethylene (4), and 1,2-bis(4-pyridyl)ethane (5)]. The complex [NiBr2(4,4'-bpy)] (6) was also obtained for comparative reasons. Compound 2 is the ß phase of the previously reported complex [NiCl2(4,4'-bpy)]. The syntheses of complexes 1-6 were carried out using solvothermal and microwave techniques. The compounds have been characterized by elemental analysis, infrared spectroscopy, thermogravimetry, and powder X-ray diffraction. The crystal structures of compounds 1, 4, and 5 have been solved using ab initio X-ray powder diffraction methods. Compounds 1-6 show the same arrangement, and their structures are described as layers formed by [NiX2] chains linked perpendicularly by N-N ligands. The magnetic properties of the compounds are explained as a balance between the ferromagnetic interactions along the [NiX2] chains and the antiferromagnetic interactions between chains from different layers. This work demonstrates that this balance can be tuned by the length of the N-N ligand.