Two classes of Ni–Ln clusters [Ln4Ni3L3(OAc)6(NO3)3(OH)3] (Ln = Gd (1) and Tb (2)) and [Ln6Ni7L6(OAc)12(OH)6](OH)2 (Ln = Gd (3) and Dy (4)) were prepared using a specifically designed Schiff base ligand built around a flexible (CH2)2O(CH2)2O(CH2)2 chain. 1 and 2 exhibit cone-like structures, while 3 and 4 have nanosized sandwich architectures. The structures were studied by single-crystal X-ray diffraction and TEM, and magnetic properties were investigated.

•A series of Re(I) complexes with substituted dppz ligands were synthesized and analyzed as electrocatalysts for CO2 reduction.•The only gaseous product CO was confirmed by GC after bulk electrolysis.•The large conjugation of dppz ligand can help store multiple electrons and lower the energy barrier for CO2 reduction.A series of rhenium(I) complexes (1–4) with substituted dipyrido[3,2-a:2′,3′-c]phenazine (dppz) ligands were synthesized and analyzed as electrocatalysts for CO2 reduction. Cyclic voltammetry study shows that complexes 1–4 exhibit dppz ligand-based and metal center-based quasi-reversible reductions under N2. Under a CO2 atmosphere, complexes 1–4 exhibit electrocatalytic response consistent with CO2 → CO reduction with the presence of the gaseous phase product CO confirmed by gas chromatography (GC). Re(2,2′-bpy)(CO)3Br (Lehn catalyst), a benchmark for electrocatalytic reduction of CO2 to CO, was also prepared and tested for electrocatalytic properties for comparison. The results suggest that chemical modification on the dppz ligand leads to interesting electrocatalytic properties and the large conjugation of the dppz ligand can help store multiple electrons and lower the energy barrier for CO2 reduction.CO2 reduction electrocatalyzed by Re(dppz) complexes in this study.Download high-res image (99KB)Download full-size image

A systematic study on the effect of variation in length of the conjugated organic backbone, and therefore the redox interactions between metal centers and the polymer backbones, of thiophene-based conducting metallopolymers (CMPs) on their charge transport properties has been conducted. Schiff-base ligands bearing various numbers of thiophene units (1–3) on both sides of a salpen center (salicyaldehyde connected through a 1,3-propylenediamine backbone) and the corresponding metal complexes of both redox-active and redox-inactive metals have been synthesized and characterized. Conducting polymers from these electropolymerizable monomers were obtained via electrochemical synthesis and studied by cyclic voltammetry, vis-NIR spectroelectrochemistry, and in situ conductivity. The results indicate that charge transport properties of ligand polymers are dramatically affected by the conjugation length of the organic backbone. The conductivity of ligand polymers increases by approximately one order of magnitude when varying the repeating units of the polymers from a bithiophene (2T) to a quarterthiophene (4T) or from a 4T to a sexithiophene (6T). However, the conductivity of the metallopolymers is significantly influenced by the interactions between the metal centers and the organic backbone. Copper(II) metallopolymers, which show no metal redox event, exhibit similar conductivity for CMPs bearing different conjugated lengths of the organic backbone. CMPs of redox-active metals (i.e., Ni(II), Co(II), and V(IV)O), on the other hand, show significant changes in conductivity depending on the relative redox potential of the metal centers and that of the organic backbone. Among metallopolymers which bear the same metal, CMPs with redox matching exhibit the highest conductivities in the series. We define redox matching as the condition in which the redox potential of the metal center is slightly higher than, but does not exceed, that of the organic backbone by ca. 0.5 V. The studies herein provide insights in understanding the structure–property relationship of CMPs, particularly on the role of the organic conjugated length, the metal centers, and metal-backbone interactions on the charge transport properties of Wolf Type III CMPs.

Four new disubstituted and monosubstituted nitro- and amino- bis(pyrazol-1-yl)pyridine (bppy) ligands, substituted at the pyrazole 4-position (1, 2, 5, 6) have been synthesized, along with two luminescent Eu(III) tris-β-diketonate derivatives of the amino substituted ligands (7, 8). The compounds have been studied using UV-Vis absorbance spectroscopy and cyclic voltammetry which has allowed for characterization of the electronic environments of these ligands. The calculated HOMO–LUMO gap values (1: 3.54 eV; 2: 3.53 eV; 5: 3.01 eV; 6: 3.66 eV) differ from that of bppy (3.86 eV) and the range is indicative that tuning of the ligand electronic environment is possible. Additionally, fluorescence spectroscopy studies were employed to determine ligand T1 energy levels of the amine-bearing ligands 2 and 6, yielding values of T1 of 25 381 cm−1 and 26 201 cm−1, respectively. These ligands were employed in the synthesis of Eu(III) complexes 7 and 8, for which the absolute and intrinsic quantum yields, lifetimes and ligand sensitization efficiencies were determined.

A series of conducting polymers, formed from an electropolymerizable Schiff-base ligand, N,N′-((2,2′-dimethyl)propyl)bis(2-thiophenyl)salcylidenimine, and the corresponding metal complexes (i.e., Ni(II), Cu(II), V(IV)═O, Co(II), and Zn(II)) have been prepared, characterized, and studied in detail. Our successful synthesis of the ligand polymer helps to make a direct comparison between the properties of metal-free conducting polymers and the corresponding metallopolymers. This enables the role of metal centers in these Schiff-base conducting metallopolymers (CMPs) in particular, and in Wolf type III CMPs in general, to be unambiguously elucidated. Vis–NIR absorption spectroelectrochemical studies show that longer distances for charge delocalization were found in the CMPs when compared to the metal-free counterpart, an indication of the contribution of the metal centers in extending the effective conjugation length of these electroactive polymers. The systematic use of both redox-active and redox-inactive first row transition metals helps to better understand the nature of charge transport and the specific role of the metal centers in these systems. Cyclic voltammetry and in situ conductivity show superior charge transport in the CMPs compared to the ligand polymer, especially in systems containing redox-active metal centers with redox potentials higher than, but similar to, that of the conjugated organic backbone. Our results indicate that inner-sphere charge transport within the organic backbone, which is serving as a hopping station, is the dominant mechanism of conductivity enhancement and favorable for efficient charge transport in Schiff-base CMPs.

Two series of Cd–Ln and Ni–Ln clusters [Ln8Cd24L12(OAc)44(48)Cl4(0)] and [Ln8Ni6L6(OAc)24(EtOH)6(H2O)2] were constructed using a flexible ligand. The Cd–Ln clusters exhibit interesting nano-drum-like structures which allows direct visualization by TEM. Luminex MicroPlex Microspheres loaded with the Cd–Sm cluster were visualized using epifluorescence microscopy. Cytotoxicity studies on A549 and AGS cancer cell lines showed that the materials have mild to moderate cytotoxicity.

Three Fe(II) bis(terpyridine)-based complexes with thiophene (Fe(L1)2), bithiophene (Fe(L2)2), and 3,4-ethylenedioxythiophene (Fe(L3)2) side chains were designed and synthesized for the purpose of providing two terminal active sites for electrochemical polymerization. The corresponding metallopolymers (poly-Fe(Ln)2, n = 2 or 3) were synthesized on indium tin oxide (ITO)-coated glass substrates via oxidative electropolymerization of the thiophene-substituted monomers and characterized using electrochemistry, X-ray photoelectron spectroscopy, UV–vis spectroscopy, and atomic force microscopy. The film poly-Fe(L2)2 was further studied for electrochromic (EC) color-switching properties and fabricated into a solid-state EC device. Poly-Fe(L2)2 films exhibit an intense MLCT absorption band at 596 nm (ε = 4.7 × 104 M–1 cm–1) in the UV–vis spectra without any applied voltage. Upon application of low potentials (between 1.1 and 0.4 V vs Fc+/Fc), the obtained electropolymerized film exhibited great contrast with a change of transmittance percentage (ΔT%) of 40% and a high coloration efficiency of 3823 cm2 C–1 with a switching time of 1 s. The film demonstrates commonplace stability and reversibility with a 10% loss in peak current intensity after 200 cyclic voltammetry cycles and almost no loss in change of transmittance (ΔT%) after 900 potential switches between 1.1 and 0.4 V (vs Fc+/Fc) with a time interval of 0.75 s. The electropolymerization of Fe(L2)2 provides convenient and controllable film fabrication. Electrochromic behavior was also achieved in a solid-state device composed of a poly-Fe(L2)2 film and a polymer-supported electrolyte sandwiched between two ITO-coated glass electrodes.Keywords: conducting metallopolymer; electrochemical polymerization; electrochromic device; electrochromic polymer; Fe bis(terpyridine) complexes;

Chromophores that incorporate f-block elements have considerable potential for use in bioimaging applications because of their advantageous photophysical properties compared to organic dye, which are currently widely used. We are developing new classes of lanthanide-based self-assembling molecular nanoparticles as reporters for imaging and as multi-functional nanoprobes or nanosensors for use with biological samples. One class of these materials, which we call lanthanide “nano-drums”, are homogeneous 4d–4f clusters approximately 25 to 30 Å in diameter. These are capable of emitting from the visible to near-infrared wavelengths. Here, we present the synthesis, crystal structure, photophysical properties and comparative cytotoxicity data for a 32 metal Eu-Cd nano-drum [Eu8Cd24L12(OAc)48] (1). We also explored the imaging capabilities of this nano-drum using epifluorescence, TIRF, and two-photon microscopy platforms.

The synthesis, crystal structures and photophysical properties of thirty-one 4f and d-4f polynuclear complexes and coordination polymers based on nine flexible salen-type ligands are described in this review. Most of these lanthanide complexes exhibit either interesting “twisted”, drum-like or polymeric structures. In these complexes, the multidentate salen-type ligands can efficiently sensitize lanthanide emissions by serving as antennas that absorb excitation light and transfer the energy to the lanthanide centers. With the lanthanide ions encapsulated by chromophoric salen-type ligands and shielded from solvent molecules which can quench the emissions from lanthanide ions, those lanthanide complexes which have “twisted” and drum-like structures show impressive luminescence properties.The synthesis, crystal structures and photophysical properties of thirty-one 4f and d-4f polynuclear complexes and coordination polymers based on nine flexible salen-type ligands are described in this review. The multidentate salen-type ligands can efficiently sensitize lanthanide emissions by serving as antennas that absorb excitation light and transfer the energy to the lanthanide centers.

Two series of Cd–Ln clusters: nano-drum [Ln8Cd24L12(OAc)48] and nano-double-drum [Ln12Cd44L20Cl30(OAc)54] (Ln = Nd and Yb) were prepared using a flexible Schiff base ligand bearing two aryl-Br groups. Chloride (Cl−) ions, together with the interactions of Br with other electronegative atoms, play a key role in the formation of the nano-double-drums. The structures were studied by TEM and photophysical properties were determined.

Two classes of heterobimetallic d–f nanoclusters [Ln6Cd24(L1)11(OAc)43(OH)] and [Ln4Zn8(L2)2(OAc)20(OH)4] (Ln = Nd and Yb) were prepared using flexible long-chain Schiff base ligands which have (CH2)6 backbones. Their NIR luminescence properties were determined.

Two series of 4d–4f clusters [Ln8Cd24L12(OAc)48] and [Ln6Cd18L9Cl8(10)(OAc)28(26)] (Ln = Nd, Gd, Er, and Yb) with novel drum-like structures were prepared using a flexible Schiff base ligand. Their NIR luminescence properties were determined.

Three isomeric water-soluble and light-stable silver(I) coordination polymers with a fluorinated carboxylate ligand were prepared by template-controlled method, which show different 2D polymeric coordination structures with a novel layered inorganic connectivity in the solid state. In water solution, they dissociate into several stable polynuclear silver(I) oligomers and exhibit extraordinary antimicrobial activities against selected bacteria.

Reactions of Co(PMe3)3Cl or CoCl2 with 3,5-(CF3)2-PzNa in hexane give Co(PMe3)3(3,5-(CF3)2-Pz) (1) and Co(PMe3)3(3,5-(CF3)2-Pz)2 (2) respectively (3,5-(CF3)2-PzNa = sodium bis-trifluoromethylpyrazolate). Reaction of (3,5-(CF3)2-PzH) with Co(PMe3)4 produces the unusual complex [cis-Co(PMe3)4H2][Co(PMe3)(3,5-(CF3)2-Pz)3] (3) which formally contains a [Co(III)]+[Co(II)]− complex ion pair. Reaction of 3,5-(CF3)2-PzLi with an oxygenated suspension of CoCl2 and 3 equivalents of PMe3 gives (3,5-(CF3)2-Pz)2Co(μ-3,5-(CF3)2-Pz)(μ-OPMe3)Li(OPMe3)2 (4), while 2 reacts with LiOH to give [(PMe3)Co(μ-3,5-(CF3)2-Pz)2(μ3-OH)Li]2 (5). Both 2 and 3 react with O2 in toluene solution to give Co(OPMe3)2(3,5-(CF3)2-Pz)2 (6). All compounds have been characterized spectroscopically and by single crystal X-ray diffraction studies.

Four Zn-Ln salen complexes are formed with the Schiff base ligand bis(3-methoxysalicylidene)ethylene-1,2-phenylenediamine (H2L). The complexes are trinuclear [LnZn2L2(OAc)2]·CF3SO3·Et2O (Ln = Eu (1) and Tb (2)), and dinuclear [EuZnL(OAc)(NO3)2MeOH] (3) and [TbZnL(OAc)2(NO3)] (4). The structures of 1–4 were determined by single crystal X-ray crystallographic studies and the respective luminescence properties in MeCN solution were determined.Graphical abstractFour Zn–Ln salen complexes are formed with the Schiff base ligand bis(3-methoxysalicylidene)ethylene-1,2-phenylenediamine (H2L). The complexes are trinuclear [LnZn2L2(OAc)2]·CF3SO3·Et2O (Ln = Eu (1) and Tb (2)), and dinuclear [EuZnL(OAc)(NO3)2MeOH] (3) and [TbZnL(OAc)2(NO3)] (4). The structures of 1–4 were determined by single crystal X-ray crystallographic studies and the respective luminescence properties in MeCN solution were determined.Highlights► Synthesis of Zn–Ln (Ln = Eu and Tb) salen complexes. ► Crystal structures of Zn–Ln salen complexes. ► Luminescence properties of Zn–Ln salen complexes.

Two classes of heterobimetallic d–f nanoclusters [Ln6Cd24(L1)11(OAc)43(OH)] and [Ln4Zn8(L2)2(OAc)20(OH)4] (Ln = Nd and Yb) were prepared using flexible long-chain Schiff base ligands which have (CH2)6 backbones. Their NIR luminescence properties were determined.

Three isomeric water-soluble and light-stable silver(I) coordination polymers with a fluorinated carboxylate ligand were prepared by template-controlled method, which show different 2D polymeric coordination structures with a novel layered inorganic connectivity in the solid state. In water solution, they dissociate into several stable polynuclear silver(I) oligomers and exhibit extraordinary antimicrobial activities against selected bacteria.

Reactions of Co(PMe3)3Cl or CoCl2 with 3,5-(CF3)2-PzNa in hexane give Co(PMe3)3(3,5-(CF3)2-Pz) (1) and Co(PMe3)3(3,5-(CF3)2-Pz)2 (2) respectively (3,5-(CF3)2-PzNa = sodium bis-trifluoromethylpyrazolate). Reaction of (3,5-(CF3)2-PzH) with Co(PMe3)4 produces the unusual complex [cis-Co(PMe3)4H2][Co(PMe3)(3,5-(CF3)2-Pz)3] (3) which formally contains a [Co(III)]+[Co(II)]− complex ion pair. Reaction of 3,5-(CF3)2-PzLi with an oxygenated suspension of CoCl2 and 3 equivalents of PMe3 gives (3,5-(CF3)2-Pz)2Co(μ-3,5-(CF3)2-Pz)(μ-OPMe3)Li(OPMe3)2 (4), while 2 reacts with LiOH to give [(PMe3)Co(μ-3,5-(CF3)2-Pz)2(μ3-OH)Li]2 (5). Both 2 and 3 react with O2 in toluene solution to give Co(OPMe3)2(3,5-(CF3)2-Pz)2 (6). All compounds have been characterized spectroscopically and by single crystal X-ray diffraction studies.

Chromophores that incorporate f-block elements have considerable potential for use in bioimaging applications because of their advantageous photophysical properties compared to organic dye, which are currently widely used. We are developing new classes of lanthanide-based self-assembling molecular nanoparticles as reporters for imaging and as multi-functional nanoprobes or nanosensors for use with biological samples. One class of these materials, which we call lanthanide “nano-drums”, are homogeneous 4d–4f clusters approximately 25 to 30 Å in diameter. These are capable of emitting from the visible to near-infrared wavelengths. Here, we present the synthesis, crystal structure, photophysical properties and comparative cytotoxicity data for a 32 metal Eu-Cd nano-drum [Eu8Cd24L12(OAc)48] (1). We also explored the imaging capabilities of this nano-drum using epifluorescence, TIRF, and two-photon microscopy platforms.

Four new disubstituted and monosubstituted nitro- and amino- bis(pyrazol-1-yl)pyridine (bppy) ligands, substituted at the pyrazole 4-position (1, 2, 5, 6) have been synthesized, along with two luminescent Eu(III) tris-β-diketonate derivatives of the amino substituted ligands (7, 8). The compounds have been studied using UV-Vis absorbance spectroscopy and cyclic voltammetry which has allowed for characterization of the electronic environments of these ligands. The calculated HOMO–LUMO gap values (1: 3.54 eV; 2: 3.53 eV; 5: 3.01 eV; 6: 3.66 eV) differ from that of bppy (3.86 eV) and the range is indicative that tuning of the ligand electronic environment is possible. Additionally, fluorescence spectroscopy studies were employed to determine ligand T1 energy levels of the amine-bearing ligands 2 and 6, yielding values of T1 of 25381 cm−1 and 26201 cm−1, respectively. These ligands were employed in the synthesis of Eu(III) complexes 7 and 8, for which the absolute and intrinsic quantum yields, lifetimes and ligand sensitization efficiencies were determined.

Two classes of Ni–Ln clusters [Ln4Ni3L3(OAc)6(NO3)3(OH)3] (Ln = Gd (1) and Tb (2)) and [Ln6Ni7L6(OAc)12(OH)6](OH)2 (Ln = Gd (3) and Dy (4)) were prepared using a specifically designed Schiff base ligand built around a flexible (CH2)2O(CH2)2O(CH2)2 chain. 1 and 2 exhibit cone-like structures, while 3 and 4 have nanosized sandwich architectures. The structures were studied by single-crystal X-ray diffraction and TEM, and magnetic properties were investigated.