Photoinduced Electron and Energy Transfer in Rigidly Bridged Ru(II)-Rh(III) Binuclear Complexes

A series of binuclear Ru(II)-Rh(III) complexes of general formula (ttpy)Ru-tpy-(ph)(n)-tpy-Rh(ttpy)(5+) (n = 0-2) have been synthesized, where ttpy = 4'-p-tolyl-2,2':6,2"-terpyridine and tpy-(ph)(n)-tpy represents a bridging ligand where two 2,2':6',2"-terpyridine units are either directly linked together (n = 0) or connected through one (n = 1) or two (n = 2) phenyl spacers in the 4'-position. This series of complexes is characterized by (i) rigid bridge structures and (ii) variable metal-metal distances (11 ? for n = 0, 15.5 ? for n = 1, 20 ? for n = 2). The photophysics of these binuclear complexes has been investigated in 4:1 methanol/ethanol at 77 K (rigid glass) and 150 K (fluid solution) and compared with that of mononuclear [Ru(ttpy)(2)(2+) and Rh(ttpy)(2)(3+)] or binuclear [(ttpy)Ru-tpy-tpy-Ru(ttpy)(4+)] model compounds. At 77 K, no quenching of the Ru(II)-based excited state is observed, whereas energy transfer from excited Rh(III) to Ru(II) is observed for all complexes. At 150 K, energy transfer from excited Rh(III) to Ru(II) is again observed for all complexes, while quenching of excited Ru(II) by electron transfer to Rh(III) is observed, but only in the complex with n = 0. The reasons for the observed behavior can be qualitatively understood in terms of standard electron and energy transfer theory. The different behavior between n = 0 and n = 1, 2 can be rationalized in terms of better electronic factors and smaller reorganizational energies for the former species. The freezing of electron transfer quenching but not of energy transfer, in rigid glasses reflects the different reorganizational energies involved in the two processes. Unusual results arising from multiphotonic and conformational effects have also been observed with these systems.     

Cyclic [2]pseudorotaxane tetramers consisting of two rigid rods threaded through two bis-macrocycles: copper(I)-templated synthesis and X-ray structure studies

Variously substituted coordinating rigid rods have been synthesized which incorporate a central 4,7-phenanthroline nucleus attached to two 2-pyridyl groups via its 3 and 8 positions, so as to yield bis-bidentate chelates, the two-coordinating axes of the chelates being parallel to one another. Regardless of the nature of the substituents borne by the rods, the copper(I)-induced threading reaction of two such rods through the rings of two bis-macrocycles affords in a quantitative yield the 4-copper(I) threaded assembly. The [2]pseudorotaxane tetramers thus obtained have been fully characterized in solution and, for one of them, an X-ray structure could be obtained, confirming the threaded nature of the complex and providing important structural information.     

Fe(II), Ru(II) and Re(I) complexes of endotopic, sterically non-hindering, U-shaped 8,8'-disubstituted-3,3'-biisoquinoline ligands: syntheses and spectroscopic properties

The redox behaviour, optical-absorption spectra and emission properties of U-shaped and elongated disubstituted biisoquinoline ligands and of derived octahedral Fe(ii), Ru(ii), and Re(i) complexes are reported. The ligands are 8,8'-dichloro-3,3'-biisoquinoline (1), 8,8'-dianisyl-3,3'-biisoquinoline (2), and 8,8'-di(phenylanisyl)-3,3'-biisoquinoline (3), and the complexes are [Fe(3)(3)](2+), [Fe(2)(3)](2+), [Ru(1)(phen)(2)](2+), [Ru(2)(3)](2+), [Ru(3)(3)](2+), [Re(2)(py)(CO)(3)](+), and [Re()(py)(CO)(3)](+). For the ligands, the optical properties as observed in dichloromethane are in line with expectations based on the predominant (1)pipi* nature of the involved excited states, with contributions at lower energies from (1)npi* and (1)ILCT (intraligand charge transfer) transitions. For all of the Fe(ii), Ru(ii), and Re(i) complexes, studied in acetonitrile, the transitions associated with the lowest-energy absorption band are of (1)MLCT (metal-to-ligand charge transfer) nature. The emission properties, as observed at room temperature and at 77 K, can be described as follows: (i) the Fe(ii) complexes do not emit, either at room temperature or at 77 K; (ii) the room-temperature emission of the Ru(ii) complexes (phi(em) > 10(-3), tau in the micros range) is of mixed (3)MLCT/(3)LC character (and similarly at 77 K); and (iii) the room-temperature emission of the Re(i) complexes (phi(em) approximately 3 x 10(-3), tau < 1 ns) is of (3)MLCT character and becomes of (3)LC (ligand-centered) character (tau in the ms time scale) at 77 K. The interplay of the involved excited states in determining the luminescence output is examined.     

Ag4V2O6F2 (SVOF): a high silver density phase and potential new cathode material for implantable cardioverter defibrillators

The electrochemical reactivity of the cathode material Ag 4V 2O 6F 2 (SVOF) versus lithium, with a particular emphasis on the lithium insertion mechanism, was studied by means of the complementary techniques in situ X-ray diffraction, electron paramagnetic resonance, and high-resolution transmisssion electron microscopy. This study confirms the initial reports of a high capacity for SVOF of 148 mAh/g above 3 V and that the reduction of silver above 3 V (vs Li (+)/Li (0)) leads to a loss of SVOF crystallinity until it becomes completely amorphous between the third and fourth lithiums inserted. Next, vanadium is reduced between 2.5 and 1.5 V (vs Li (+)/Li (0)) for the fifth and sixth lithiums inserted. In addition, the polarization within the cathode is significantly lower for the vanadium reduction than for the silver reduction. The silver metal morphologies consisted of nanoparticles ( approximately 5 nm diameter) and dendrites and were both seen in samples of lithiated SVOF.     

A study by spectroelectrochemical FTIR and density functional theory calculations of the reversible complexing ability of an electroactive tetrathiafulvalene crown

We report on the study of the electrochemically targeted complexation/expulsion of a metal cation (Ba2+) by a crown ether tetra(thiomethyl)tetrathiafulvalene derivative (crown-TTM-TTF). Real time, in situ FTIR spectroelectrochemistry was used to obtain spectroscopic evidence of this electrochemically triggered phenomenon. Density functional theory calculations allowed the spectral information collected to be assigned. Both experimental and theoretical results clearly show that neutral crown-TTM-TTF complexes well Ba2+. Complexation is evidenced by a significant downshift of the frequency corresponding to the asymmetric stretching of the C-O-C ether groups. Concerning the cation crown-TTM-TTF, the spectroscopic signal of the complex form was difficult to identify, first because of the rather low value of the complexation constant and second because the vibration modes involving the oxygen atoms (which are the most affected by the complexation) were found by calculation to occur in the lower spectral region (<1000 cm(-1)), which is not accessible in our experimental conditions. In the case of the dication crown-TTM-TTF, it is now clear that the complex form does not exist, which means that the electrochemical formation of the dication necessarily involves the expulsion of the barium ion.     

A catenane consisting of a large ring threaded through both cyclic units of a handcuff-like compound

The template effect of copper(I) allowed the preparation of a new catenane constructed around a bis-macrocyclic unit; a double ring-closing metathesis reaction afforded the central ring which is threaded through both rings of the bis-macrocycle.     

α-Unsaturated 3-Amino-1-carboxymethyl-β-lactams as Bacterial PBP Inhibitors: Synthesis and Biochemical Assessment

Innovative monocyclic β-lactam entities create opportunities in the battle against resistant bacteria because of their PBP acylation potential, intrinsically high β-lactamase stability and compact scaffold. α-Benzylidene-substituted 3-amino-1-carboxymethyl-β-lactams were recently shown to be potent PBP inhibitors and constitute eligible anchor points for synthetic elaboration of the chemical space around the central β-lactam ring. The present study discloses a 12-step synthesis of ten α-arylmethylidenecarboxylates using a microwave-assisted Wittig olefination as the crucial reaction step. The library was designed aiming at enhanced β-lactam electrophilicity and extended electron flow after enzymatic attack. Additionally, increased β-lactamase stability and intermolecular target interaction were envisioned by tackling both the substitution pattern of the aromatic ring and the β-lactam C4-position. The significance of α-unsaturation was validated and the R39/PBP3 inhibitory potency shown to be augmented the most through decoration of the aromatic ring with electron-withdrawing groups. Furthermore, ring cleavage by representative β-lactamases was ruled out, providing new insights in the SAR landscape of monocyclic β-lactams as eligible PBP or β-lactamase inhibitors.