Neutral Paddlewheel Diruthenium Complexes with Tetracarboxylates of Large π-Conjugated Substituents: Facile One-Pot Synthesis, Crystal Structures, and Electrochemical Studies

Redox-Active Ruthenium-Organic Polyhedra with Tunable Surface Functionality and Porosities

Dinuclear ruthenium paddlewheel complexes exhibit high structural stability in redox reactions. The use of these chemical motifs for the construction of Ru-based metal-organic polyhedra (RuMOPs) provides a route for redox-active porous materials. However, there are few studies on the synthesis and characterization of RuMOPs due to the difficulty in controlling the assembly process via the ligand-exchange reaction of equatorial acetates of the diruthenium tetraacetate precursors with dicarboxylic acid ligands. In this study, we synthesized three novel cuboctahedral RuMOPs based on the Ru2(II/III)-paddlewheel units with different alkyl functionalizations on the benzene-1,3-dicarboxylate moieties. We evaluated the effect of external functionalization on the molecular packing and the porous and redox properties. The electrochemical measurements revealed the multielectron transferred redox process where the electron-donating/-withdrawing nature of the functional groups allows the control of the redox behavior.

Post-synthetic molecular modifications based on Schiff base condensation reactions for designing functional paddlewheel diruthenium(II,II) complexes

A new synthetic route for constructing functional paddlewheel diruthenium(II,II) complexes ([RuII,II2]) was developed by utilizing Schiff base condensation reactions of formyl-substituted benzoate-bridged [RuII,II2] complexes with various aromatic monoamines under mild conditions. Cyclic voltammetry and DFT calculations revealed that the attached Schiff base groups significantly affected the electronic states of the resulting [RuII,II2] complexes.

Porous supramolecular gels produced by reversible self-gelation of ruthenium-based metal-organic polyhedra

Supramolecular gels based on metal-organic polyhedra (MOPs) represent a versatile platform to access processable soft materials with controlled porosity. Herein, we report a self-gelation approach that allows the reversible assembly of a novel Ru-based MOP in the form of colloidal gels. The presence of cationic mixed-valence [Ru2(COO)4]+ paddlewheel units allows for modification of the MOP charge via acid/base treatment, and therefore, its solubility. This feature enables control over supramolecular interactions, making it possible to reversibly force MOP aggregation to form nanoparticles, which further assemble to form a colloidal gel network. The gelation process was thoroughly investigated by time-resolved ζ-potential, pH, and dynamic light scattering measurements. This strategy leads to the evolution of hierarchically porous aerogel from individual MOP molecules without using any additional component. Furthermore, we demonstrate that the simplicity of this method can be exploited for the obtention of MOP-based gels through a one-pot synthetic approach starting from MOP precursors.

trans-Heteroleptic carboxylate-bridged paddlewheel diruthenium(ii, ii) complexes with 2,6-bis(trifluoromethyl)benzoate ligands

Carboxylate-ligand substitution reactions of paddlewheel-type diruthenium(ii, iii) complexes ([Ru(RCO2)4](+)) with 2,6-bis(trifluoromethyl)benzoate (2,6-(CF3)2PhCO2(-)) involving a selective reduction to [Ru] provide a series of trans-substituted paddlewheel-type diruthenium(ii, ii) complexes, [Ru(2,6-(CF3)2PhCO2)2(RCO2)2(THF)2] (R = CH3, ; C2H5, ; C3H7, ; C4H9, ; C(CH3)3, ; 2,3,5,6-F4Ph, ). Crystal structures of were determined, and their electronic states were investigated by cyclic voltammetry, density functional theory (DFT) and magnetic measurements. This is the first example of trans-heteroleptic carboxylate-bridged [Ru] complexes.

An unprecedented up-field shift in the 13C NMR spectrum of the carboxyl carbons of the lantern-type dinuclear complex TBA[Ru2(O2CCH3)4Cl2] (TBA+ = tetra(n-butyl)ammonium cation)

A large up-field shift (-763 ppm) has been observed for the carboxyl carbons of the dichlorido complex TBA[Ru(2)(O(2)CCH(3))(4)Cl(2)] (TBA(+) = tetra(n-butyl)ammonium cation) in the (13)C NMR spectrum (CD(2)Cl(2) at 25 °C). The DFT calculations showed spin delocalization from the paramagnetic Ru(2)(5+) core to the ligands, in agreement with the large up-field shift.

The effect of chlorine and fluorine substitutions on tuning the ionization potential of benzoate-bridged paddlewheel diruthenium(ii, ii) complexes

A series of paddlewheel diruthenium(ii, ii) complexes with various chlorine-substituted benzoate ligands (Cl-series) was synthesized as tetrahydrofuran (THF) adducts [Ru2(ClxPhCO2)4(THF)2]; where ClxPhCO2(-) = o-chlorobenzoate, ; m-chlorobenzoate, ; p-chlorobenzoate, ; 2,3-dichlorobenzoate, ; 2,4-dichlorobenzoate, ; 2,5-dichlorobenzoate, ; 2,6-dichlorobenzoate, ; 3,4-dichlorobenzoate, ; 3,5-dichlorobenzoate, ; 2,3,4-trichlorobenzoate, ; 2,3,5-trichlorobenzoate, ; 2,4,5-trichlorobenzoate, ; 3,4,5-trichlorobenzoate, ; 2,3,4,5-tetrachlorobenzoate, . This Cl-series and the previously synthesized F-series together with four new fluorine-substituted derivatives, [Ru2(FxPhCO2)4(THF)2] (where FxPhCO2(-) = 2,3-difluorobenzoate, ; 2,4-difluorobenzoate, ; 2,5-difluorobenzoate, ; 2,3,5-trifluorobenzoate, ), were experimentally characterized with respect to solid-state structure, magnetic properties and electrochemistry. By tuning the substituents of the benzoate ligands using chlorine or fluorine atoms, the redox potential (E1/2) for [Ru2(II,II)]/[Ru2(II,III)](+) varied over a wide range of potentials from -40 mV to 360 mV (vs. Ag/Ag(+) in THF). This was dependent on (i) the number of ortho-substituents, i.e. non-, mono- and di-o-substituted groups, with quasi-Hammett parameters for ortho-Cl and -F substitutions (σo = -0.272 and -0.217, respectively) and (ii) the general Hammett constants, σm and σp, for each group. The HOMO energy level calculated on the basis of the atomic coordinates of the solid-state structure was strongly affected by Cl- and F-substitutions as well as the redox potential in solution, which emphasizes the steric contribution of ortho-substituents in the energy level giving a deviation of EHOMO < 0.3 eV and <0.55 eV for the Cl- and F-series, respectively.

Magnetic and Electronic Properties of Three New Hetero-Bimetallic Coordination Frameworks [Ru2(O2CR)4][Au(CN)2] (R = Benzoic Acid, Furan-2-carboxylate, or Thiophen-2-carboxylate)

The crystal structures and magnetic and electronic properties of three new hetero-bimetallic coordination frameworks, [Ru2(O2CR)4][Au(CN)2] (R = phenyl (1(Ph)), 2-furan (1(Furan)), and 2-thiophene (1(Thio)), have been characterised. Through variation of the functionalised carboxylate group, both the one-dimensional chain structure and properties of the frameworks have been systematically modulated. The magnetic behaviour for each framework has been modelled with a zero-field splitting model and the presence of weak inter-dimer coupling was assessed.

Template- and pH-Directed Assembly of Diruthenium Diphosphonates with Different Topologies and Oxidation States

In the presence of organic templates, six diruthenium diphosphonates, namely, [H3N(CH2)3NH3]2[Ru2(hedp)2] (1), [H3N(CH2)4NH3]2[Ru2(hedp)2].4H2O (2), [H3N(CH2)5NH3]2[Ru2(hedp)2].4H2O (3), [H3N(CH2)3NH3][Ru2(hedp)(hedpH)].H2O (4), [H3N(CH2)4NH3][Ru2(hedpH(0.5))2].2H2O (5), and [H3N(CH2)5NH3]2[Ru2(hedp)2][Ru2(hedpH)2]] (6) [hedp = 1-hydroxyethylidenediphosphonate, CH3C(OH)(PO3)2] have been synthesized under hydrothermal conditions. Compounds 1-3 contain homovalent paddlewheel cores of Ru2(II,II)(hedp)2(4-) that are connected through edge-sharing of the [RuO5Ru] octahedra, resulting in infinite linear chains. Compounds 4-6 contain mixed-valent diruthenium(II,III) phosphonate paddlewheel cores of Ru2(II,III)(hedpH(n))2(3-2n)- that are connected by phosphonate oxygen atoms, forming distorted square-grid layers in 4 and 6 or a kagomé lattice in 5. Both the templates and the pH values are found to play important roles in directing the final products with particular topologies and oxidation states of the diruthenium unit. The magnetic studies show that weak antiferromagentic interactions are propagated between the homovalent diruthenium units in compounds 1-3. For compounds 4-6, weak ferromagnetic interactions are observed.

Observation of 1MLCT and 3MLCT excited states in quadruply bonded Mo2 and W2 complexes

The photophysical properties of the series of quadruply bonded M(2)(O(2)C-Ar)(4) [M = Mo, Ar = phenyl (ph), 1-naphthalene (1-nap), 2-naphthalene (2-nap), 9-anthracene (9-an), 1-pyrene (1-py), and 2-pyrene (2-py); M = W, Ar = ph, 2-nap] complexes were investigated. The lowest energy absorption of the complexes is attributed to a metal-to-ligand charge transfer (1)MLCT transition from the metal-based delta HOMO to the pi* O(2)C-Ar LUMO. The Mo(2)(O(2)C-Ar)(4) complexes exhibit weak short-lived emission (<10 ns) and a nonemissive, long-lived (40-76 mus) excited state detected by transient absorption spectroscopy. The short- and long-lived species are attributed to the (1)MLCT and (3)MLCT excited states, respectively, based on the large Stokes shift, vibronic progression in the low-temperature emission spectrum, and solvent dependence. Comparisons are made to the W(2)(O(2)C-Ar)(4) complexes, which are easier to oxidize and exhibit greater spin-orbit coupling than the Mo(2) systems. From the excited-state energy of the emissive (1)MLCT state and the electrochemical properties of the complexes, it is predicted that this excited state should be a powerful reducing agent. The crystal and molecular structure of Mo(2)(O(2)C-9-an)(4) is also reported together with electronic structure calculations employing density functional theory. To our knowledge, this is the first observation of MLCT excited states in quadruply bonded complexes. In addition, the photophysical properties of the present systems parallel those of organic aromatic molecules and may be viewed as metal-mediated organics. The introduction of the M(2) delta orbital in the complexes in conjugation with the organic pi-system of the ligands affords the opportunity to tune the excited-state energies and redox potentials.

Unligated Diruthenium(II,II) Tetra(trifluoroacetate): The First X-ray Structural Study, Thermal Compressibility, Lewis Acidity, and Magnetism

The title compound, [Ru(2)(O(2)CCF(3))(4)] (1), has been obtained without any exogenous ligands and crystallized by deposition from the gas phase at 170 degrees C. Its crystal structure has been determined for the first time to confirm an infinite chain motif built on axial Ru...O interactions of the diruthenium(II,II) units. The X-ray diffraction studies at variable temperatures showed no phase transitions in the range of 295-100 K but revealed a significant decrease in the volume per atom from 14.2 to 13.3 A(3). This noticeable thermal compressibility effect is discussed in connection with the solid-state packing of the [Ru(2)(O(2)CCF(3))(4)](infinity) chains. The highly electrophilic character of the diruthenium(II,II) units has been shown by the gas-phase deposition reaction of [Ru(2)(O(2)CCF(3))(4)] with an aromatic donor substrate, namely [2.2]paracyclophane (C(16)H(16)). As a result of the above reaction, a new arene adduct [Ru(2)(O(2)CCF(3))(4).C(16)H(16)] (2) has been isolated in crystalline form. It has an extended one-dimensional (1D) chain structure comprised of alternating building units and based on the rare bridging mode of [2.2]paracyclophane, [Ru(2)(O(2)CCF(3))(4).(mu(2)-eta(2):eta(2)-C(16)H(16))](infinity). The magnetic susceptibility of 1 and 2 has been measured and compared in the range of 1.8-300 K. In addition, in the course of synthesis of 1 by the carboxylate exchange reactions, a new mixed-carboxylate diruthenium(II,II) core complex [Ru(2)(O(2)CCF(3))(3)(O(2)CC(2)H(5))] (3), bearing no exogenous ligands, has also been isolated and structurally characterized. It exhibits an interesting polymeric structure in which the ruthenium(II) centers selectively form axial interdimer contacts with the O-atoms of the propionate groups only.

Diosmium(III) Compounds Supported by 2-Anilinopyridinate and Novel Alkynyl Derivatives

The reaction between Os(2)(OAc)(4)Cl(2) and Hap (Hap is 2-anilinopyridine) under prolonged refluxing conditions resulted in an Os(III)(2) compound, Os(2)(ap)(4)Cl(2) (1), that can be crystallized as either the cis-(2,2) isomer from a CH(3)OH-CH(2)Cl(2) solution or the (3,1) isomer from a hexanes-CH(2)Cl(2) solution. Compound 1 undergoes facile reactions with LiC(2)Y to yield a series of Os(2)(ap)(4)(C(2)Y)(2) compounds with Y as Ph (2), ferrocenyl (3), SiMe(3) (4), and C(2)SiMe(3) (5). X-ray diffraction study of compound 2 reveals solvent-dependent isomerism similar to that of the parent compound 1. Compound 1 has Os-Os distances of 2.3937(8) and 2.3913(8) Angstroms for the cis-(2,2) and (3,1) isomers, respectively, and is paramagnetic (S = 1). Both the ethynyl derivatives 2-4 and butadiynyl derivative 5 are diamagnetic and have Os-Os distances of 2.456(1), 2.471(1), and 2.481(1) Angstroms for the cis-(2,2) and (3,1) isomers of 2 and (3,1) isomer of 4, respectively. Compounds 1-5 exhibit multiple one-electron redox couples in their cyclic voltammograms, including a reversible Os(2)(8+/7+) couple for 2. Resonance Raman spectra of both compounds 1 and 2 are reported.