A Dinuclear Double-Stranded Oxido Complex of ReVwith a Bis(benzene-o-dithiolato) Ligand

Amide-Functionalized Chalcogen-Bridged Flexible Tetranuclear Rhenacycles: Synthesis, Characterization, Solvent Effect on the Structure, and Guest Binding

The synthesis of flexible rhenium(I)-based amide-functionalized chalcogen-bridged tetranuclear metallacycles of general formula [{(CO)₃Re(μ-ER)₂Re(CO)₃}₂(μ-L)₂] (1-8) was achieved by treating rhenium carbonyl with dialkyl/diaryl chalcogenide (RE-ER; E = S and Se) in the presence of ditopic flexible or semiflexible pyridyl ligand with amide functionality (L = N,N'-bis(4-pyridylcarboxamide)-1,2-ethane (bpce) and N,N'-bis(4-(4-pyridylcarboxamide)phenyl)methane (bpcpm)). Compounds 1-8 were formed by multicomponent self-assembly under one-pot reaction conditions via oxidative addition of dialkyl/diaryl chalcogenide to rhenium carbonyl with pyridyl ligands. The resultant metallacyclophanes were characterized using elemental analyses, infrared, ultraviolet-visible, and NMR spectroscopic techniques. Metallacyclophanes 1-3 and 7 were structurally characterized by single-crystal X-ray diffraction methods. The solvent-induced structural change of flexible tetranuclear metallacyclophane 2 was demonstrated by crystallizing 2 in dichloroethane and dimethylformamide. Molecular recognition capabilities of 2 and 7 were studied with few aromatic compounds containing ethereal linkages.

(99m)Tc SPECT imaging agent based on cFLFLFK for the detection of FPR1 in inflammation

Non-invasive imaging of the inflammatory process can provide great insight into a wide variety of disease states, aiding diagnosis, evaluation and effective targeted treatment. During inflammation, blood borne leukocytes are recruited, through a series of activation and adhesion steps, to the site of injury or infection where they migrate across the blood vessel wall into the tissue. Thus, tracking leukocyte recruitment and accumulation provides a dynamic and localised read out of inflammatory events. Current leukocyte imaging techniques require ex vivo labelling of patient blood, involving laborious processing and potential risks to both patient and laboratory staff. Utilising high affinity ligands for leukocyte specific receptors may allow for injectable tracers that label leukocytes in situ, omitting potentially hazardous ex vivo handling. Formyl peptide receptors (FPRs) are a group of G-protein coupled receptors involved in the chemotaxis and inflammatory functioning of leukocytes. Highly expressed on leukocytes, and up-regulated during inflammation, these receptors provide a potential target for imaging inflammatory events. Herein we present the synthesis and initial in vitro testing of a potential Single Photon Emission Computed Tomography (SPECT) leukocyte tracer. The FPR1 antagonist cFLFLFK-NH2, which displays high affinity with little physiological effect, has been linked via a PEG motif to a (99m)Tc chelate. This tracer shows in vitro binding to human embryonic kidney cells expressing the FPR1 receptor, and functional in vitro tests reveal cFLFLFK-NH2 compounds to have no effect on inflammatory cell functioning. Overall, these data show that (99m)Tc.cFLFLFK-NH2 may be a useful tool for non-invasive imaging of leukocyte accumulation in inflammatory disease states.

Nickel(II) complexes with methyl(2-pyridyl)ketone oxime: synthesis, crystal structures and DFT calculations

The synthesis and structural characterization of the three novel nickel(II) complexes [Ni(OOCPh)(2)(mpkoH)(2)] (1), [Ni(NO(3))(2)(mpkoH)(2)] (2) and [Ni(mpkoH)(3)](NO(3))(2)·½H(2)O (3·½H(2)O), with mpkoH=methyl(2-pyridyl)ketone oxime is reported. Geometry optimization and population analyses were performed by means of DFT calculations for the previously mentioned compounds as well as for [NiCl(2)(mpkoH)(2)] (4). Electronic UV-vis spectra were also simulated in the TD-DFT framework to assign the origin of the absorption bands and in doing so, to have a clear picture of the absorptive features of the coordination compounds under investigation.

Dinuclear triple-stranded complexes of Re(V) with bis(benzene-o-dithiolato) ligands

The reaction of K(2)ReCl(6) with 1,2-bis(2,3-dimercaptobenzamido)ethane (H(4)-1), and 1,2-bis(2,3-dimercaptobenzamido)benzene (H(4)-2) in the presence of Na(2)CO(3) in methanol affords dinuclear complexes of Re(V). Experimental evidence supports the presence of self-assembled complexes with two {Re(S(2)C(6)H(3))(3)} units connected in a triple-stranded fashion. Density Functional Theory (DFT) studies on geometry and electronic properties were conducted employing the hybrid B3LYP and PBE1PBE functionals. The helical (ΔΔ and ΛΛ) and meso-helical (ΔΛ) isomers were considered. For the helicate complexes included in this study, differences in the stability of the isomers were observed originating in different steric and strain interactions between the three ligand strands. The geometries at the minimum exhibit a distorted trigonal-prismatic coordination environment at the metal centers. Natural bond orbitals (NBO) analysis indicates the presence of Re-S bonds which are strongly polarized toward the non-metal. Time-Dependent DFT (TD-DFT) calculations were performed for a further understanding of the optical spectra. The calculations show the occupied 5d orbitals of the rhenium lying beneath occupied sulfur-based MOs. The general features of the electronic spectra in the visible region are reasonably reproduced by the calculations. The analysis of molecular orbitals also allows the assignment of the origin for all experimentally detected absorption bands. In the high-energy region of the spectrum the absorptions are attributed to ligand-to-metal-ligand charge transfer (LMLCT), in which sulfur-based orbitals and unoccupied orbitals at the rhenium atom and the benzene-o-dithiolato groups are involved. Also in the blue region, shoulders originating from LMLCT are observed.

TD-DFT investigation of triple-stranded helicates with bis(benzene-o-dithiolato) ligands

The electronic spectra of triple-stranded complexes of Ti(IV) with bis(benzene-o-dithiolato) ligands (H(4)-L(1)=1,2-bis(2,3-dimercaptobenzamido)ethane; H(4)-L(2)=1,2-bis(2,3-dimercaptobenzamido)benzene) were investigated at the TD-DFT level of theory employing B3LYP/LANL2DZ. The influence of the nature (aliphatic or aromatic) of the spacer bridging both {Ti(S(2)C(6)H(3))(3)} units on the absorptive features of the dinuclear complexes was also studied. B3LYP/LANL2DZ leads to spectra accounting for four absorption bands. At the lowest-energy region, the most important transitions are due to ligand-to-metal charge transfer (LMCT), in which out-of-plane ligand-centered orbitals and titanium-based MOs are involved. In going to the blue-region, a third band was detected with excitations showing an important contribution from ligand-to-ligand charge transfer (LLCT) and indeed, a combined LMCT+LLCT character has been considered. This observation seems to arise from a decrease in the metallic character of the LUMO-derivatives involved in the excitations. The origin of the absorption band at the highest-energy part of the spectrum is assigned to a LLCT. The influence of the nature of the spacer on the molar absorption coefficients (ɛ) for this band has been clearly observed. The complex bearing aliphatic spacer shows ɛ of about 5 E+4 M(-1) cm(-1), while the one containing an aromatic spacer present a value of ɛ of about 2 E+5 M(-1) cm(-1).

Time-dependent density functional theory investigation of the electronic spectra of hexanuclear chalcohalide rhenium(III) clusters

The UV-vis spectra of the hexanuclear chalcohalide rhenium(III) clusters of formula [Re(6)S(8)X(6)](4-) (X(-) = Cl(-), Br(-), I(-)) were investigated at the time-dependent density functional theory (TD-DFT) level employing B3LYP, PBE1PBE, and the double-hybrid B2PLYP functional in combination with the LANL2DZ basis set. We were able to reproduce the red shift experimentally observed when the halide changes from chloride to iodide. However, some discrepancies between experimental results and theory were found. First, we did not observe a remarkable dependence of the experimental ill-resolved bands on the solvent. Indeed, similar spectra were obtained taken CH(2)Cl(2) or CH(3)CN as solvents into account. Second, all calculations explained the origin of the band peaked at the low-energy region in contraposition with the one experimentally assumed by R. Long et al. (J. Am. Chem. Soc. 1996, 118, 4603), and theoretically made available by Arratia-Pérez et al. (J. Chem. Phys. 1999, 110, 2529). These authors have proposed a ligand-to-cluster charge transfer (LCCT) for all title complexes. Our findings undoubtedly allow such origin to be discarded. While the HGGA functionals lead to a cluster-to-halide ligand charge transfer (CLCT), an intracluster charge transfer (ICCT) has been considered by employing B2PLYP. This contribution showed B2PLYP in the presence of the solvent to be the best performer in studying the UV-vis spectra of large complexes of rhenium(III) containing the Re-S bond. We strongly recommended the use of the double-hybrid B2PLYP in studying UV-vis spectrum of rhenium complexes of size making the computational cost affordable. We expect that our work stimulates new experimental and theoretical investigations of the title complexes to confirm our assignment.

Electronic spectra of oxocomplexes of Re(V) with thiolato ligands

The electronic spectra of monooxo complexes of rhenium(V) with 1,2-benzenedithiolato (bdt(2-)), 3,4-toluenenedithiolato (tdt(2-)), maleonitriledithiolato (mnt(2-)), and 1,2-dithiooxalato (dto(2-)) ligands were investigated at the TD-DFT level employing several functionals and basis sets. The most important transitions are due to ligand-to-metal charge transfer (LMCT) with some minor contribution of ligand-to-metal-ligand charge transfer (LMLCT). However, for [ReO(dto)(2)](-) this statement does not hold because the transitions are due to metal-ligand-to-metal-ligand charge transfer (MLMLCT). This observation arises from the presence of the oxalate groups. These substituents increase the flexibility of this complex with respect to the complexes containing bdt(2-), mnt(2-) and tdt(2-). In these complexes, the C-C backbone imposes a rigid geometry, which leads to the occupied rhenium-orbitals lying energetically below the sulfur-based orbitals. For the complexes [ReO(bdt)(2)](-), [ReO(mnt)(2)](-) and [ReO(tdt)(2)](-), the HOMO is a sulfur-based out-of-plane molecular orbital. However, the HOMO of [ReO(dto)(2)](-) shows a high contribution of the rhenium d(x)(2)(-y)(2) and in-plane sulfur-centered orbitals. The comparison of the results obtained with several functionals clearly point to the PBE1PBE/LANL2DZ method as the best TD-DFT method to investigate the electronic spectra of monooxo complexes of Re(V) with thiolato ligands. The results obtained with larger basis sets suggest that the agreement between experiment and theory was due to an error cancellation between basis set incompleteness and deficiencies in the DFT methods.