Dinuclear rhenium pyridazine complexes containing bridging chalcogenide anions : synthesis, characterization and computational study

The synthesis of a series of neutral dinuclear rhenium complexes of the general formula [Re2(m-ER)2(CO)6- (m-pydz)] (pydz = pyridazine; E = S, Se or Te; R = methyl or phenyl; the TeMe is not included) has been carried out via new, either one-pot or two-step, procedures. The one-pot synthesis consists of the oxidative addition of RE\u2013ER across the Re\u2013Re bond of [Re2(CO)10], in the presence of 1 equivalent of pyridazine, and affords the corresponding dinuclear complexes in high yields (ca. 85%). Furthermore, a general two-step procedure has been carried out, which involves the synthesis of heterocubane-like [Re4(m3-ER)4(CO)12] molecules and their reaction with pyridazine, quantitatively affording the corresponding dinuclear species through a symmetric [2+2] fragmentation pathway. The molecular structure of the complexes has been elucidated by single crystal XRD analysis, and TD-DFT calculations predicted the existence of conformers differing in the orientation of the chalcogen substituents with respect to the pyridazine ligand. The relative stabilities and the activation barriers for the interconversion have been calculated, observing a regular trend that has been rationalized depending on the hybridization of the chalcogen atom. Variable temperature NMR studies experimentally confirmed the theoretical prediction, showing, in solution, two conformers with different relative amounts and different interconversion rates between them, depending on the chalcogen nature. From the electrochemical point of view the S, Se and Te complexes display a bi-electronic reversible oxidation peak, differently from the two mono-electronic irreversible oxidation peaks previously observed for the O derivatives. Moreover, a progressive narrowing of the HOMO\u2013LUMO gap on going from O to Te, arising from the increase of the HOMO level, has been observed. This is in line with the decreasing electron-withdrawing strength of the chalcogenide bridging ligand, so that the energy gap for the telluride derivative is 1.64 eV, the smallest value in the whole family of the di-rhenium pyridazine complexes. The spectroscopic HOMO\u2013LUMO gap parallels this trend, with a significant red-shift of the metal-to-ligand charge transfer absorption, making the telluride complex highly promising as a photosensitizer in the field of solar energy conversion. In agreement with the narrow HOMO\u2013LUMO gap, no photoluminescence has been observed upon optical excitation

Electrochemical Characterization and CO2 Reduction Reaction of a Family of Pyridazine-Bridged Dinuclear Mn(I) Carbonyl Complexes

Three recently synthesized neutral dinuclear carbonyl manganese complexes with the pyridazine bridging ligand, of general formula [Mn2(μ-ER)2(CO)6(μ-pydz)] (pydz = pyridazine; E = O or S; R = methyl or phenyl), have been investigated by cyclic voltammetry in dimethylformamide and acetonitrile both under an inert argon atmosphere and in the presence of carbon dioxide. This family of Mn(I) compounds behaves interestingly at negative potentials in the presence of CO2. Based on this behavior, which is herein discussed, a rather efficient catalytic mechanism for the CO2 reduction reaction toward the generation of CO has been hypothesized

Dinuclear Re(I) Complexes as New Electrocatalytic Systems for CO2 Reduction

A family of dinuclear tricarbonyl rhenium (I) complexes containing bridging 1,2-diazine ligand and halide anions as ancillary ligands and able to catalyze CO2 reduction is presented. Electrochemical studies show that the highest catalytic efficiency is obtained for the complex containing the 4,5-bipenthyl-pyridazine and iodide as ancillary halogen ligands. This complex gives rise to TOF=15 s−1 that clearly outperforms the values reported for the benchmark mononuclear Re(CO)3Cl(bpy) (11.1 s−1). The role of the substituents on the pyridazine ligand and the nature of the bridging halide ligands on the catalytic activity have been deeply investigated through a systematic study on the structure-properties relationship to understand the improved catalytic efficiencies of this class of complexes

Dirhenium Coordination Complex Endowed with an Intrinsically Chiral Helical-Shaped Diphosphine Oxide

A one-pot, multicomponent strategy was used to synthesize the first example of the dirhenium carbonyl coordination complex 2, in which the two metal atoms are connected through a chiral helical-shaped diphosphine oxide. Thanks to the flexibility of the helix of helicene 1, complex 2 was isolated in quite a good yield as a stable compound. It was characterized by analytical and spectroscopic techniques as well as by single-crystal X-ray analysis, which confirmed the chemical structure and the peculiar architecture of 2. In addition, computational studies were in agreement with the transitions observed in the experimental UV\u2013vis spectrum, revealing the presence of two bands with maxima at about 520 (metal-to-ligand charge transfer) and 400 nm (IL

Biophysical characterisation, antitumor activity and MOF encapsulation of a half-sandwich ruthenium(ii) mitoxantronato system

The novel non-conventional metallodrug [(\u3b76-p-cymene)2Ru2mitoxantronato]Cl2 (1) exhibits redox activity, DNA intercalation ability, cathepsin B and D inhibition and in vitro antitumor activity able to circumvent cisplatin resistance. Moreover, 1 can be successfully incorporated into MIL100(Fe) as a proof of concept of the feasibility of metal\u2013organic frameworks as carriers of non-conventional drugs

Molecular architecture of redox-active half-sandwich Ru(ii) cyclic assemblies : interactions with biomolecules and anticancer activity

Tetranuclear cationic open boxes non-covalently bind DNA major groove. By contrast, they covalently bind cysteine after ligand exchange reactions. In addition, these systems exhibit potent antitumour activity circumventing cisplatin resistance

A highly porous interpenetrated MOF-5-type network based on bipyrazolate linkers

A novel cobalt(II) metal organic framework containing two interpenetrated nets with the cubic pcu-a topology of MOF-5 has been synthesized and characterized. In spite of being interpenetrated, this material exhibits a highly accessible porous structure

Luminescent conjugates between dinuclear rhenium complexes and 17α-ethynylestradiol: synthesis, photophysical characterization, and cell imaging

Three new luminescent conjugates between dinuclear rhenium complexes and an estradiol, namely E2-Re, are described. The derivatives have the general formula [Re2(\u3bc-Cl)2(CO)6(\u3bc-R-pydz-17\u3b1-ethynylestradiol)] (R-pydz = functionalized 1,2-pyridazine), where the estradiol moiety is covalently bound to the \u3b2 position of the pyridazine ligand. Different synthetic pathways are investigated, including the inverse-type [4 + 2] Diels Alder cycloaddition reaction between the electron poor 1,2,4,5-tetrazine and 17\u3b1-ethynylestradiol for the synthesis of E2-Re1. The three E2-Re conjugates are purified on silica gel and isolated in a spectroscopically pure form in moderate to good yields (28-50%). All the E2-Re conjugates are comprehensively characterized from the spectroscopic and photophysical points of view. Cellular internalization experiments on human MCF-7 and 231 cells are also reported, displaying interesting staining differences depending on the nature of the spacer linking the estradiol unit to the organometallic fragment. Furthermore, the suitability of these conjugates to also stain simple multicellular organisms, i.e. Ciona intestinalis embryos and larvae at different stages of development, is reported here for the first time

A novel third-generation Cu-PCP with unprecedented m-OH2 bridge

Soft porous coordination polymers (Soft-PCPs) also known as third-generation porous materials (i.e. undergoing reversible transformations accompanied by structural modifications) are the subject of high interest as a consequence of their unique properties. These materials have a kind of \u201csoft\u201d periodic network with bistability associated to a contracted or expanded phase, as a response to external stimuli. In this communication, we present the new Cu-PCP of formulation ([Cu2(dmcapz)2(OH2)]DMF1.5)n (1) easily obtained in the reaction of CuCl2 with 3,5-dimethyl-4-carboxypyrazole (H2dmcapz). 1 shows an unprecedented H2O bridge between the two metal atoms. The removal of this water molecule gives rise to a metastable evacuated phase (1b) that transforms into an empty and extremely stable material (1c) after freezing at liquid nitrogen temperature (see Scheme). The soaking of 1c into water, allows the complete and instantaneous recover of the water exchanged material 1a. Noteworthy, 1c is very stable in air since ambient moisture cannot transform it into 1a, due to the need of high water pressures to achieve the gate opening. The key factor of these reversible phase changes in 1 is the flexible nature of Cu(II) coordination polyhedron which is able to adapt to various coordination numbers and geometries. Noteworthy, the changes in the coordination sphere of Cu are confirmed by marked colour changes. The relation between the Cu coordination geometries and the 3D structure are under investigation, as well as the differences in gas adsorption properties of 1b and 1c evacuated materials