Photofunctions in Hybrid Systems of Schiff Base Metal Complexes and Metal or Semiconductor (Nano)Materials

Composite materials very often provide new catalytic, optical or other physicochemical properties not observed for each component separately. Photofunctions in hybrid systems are an interesting topic of great importance for industry. This review presents the recent advances, trends and possible applications of photofunctions of hybrid systems composed of Schiff base metal complexes and metal or semiconductor (nano)materials. We focus on photocatalysis, sensitization in solar cells (DSSC-dye sensitized solar cell), ligand-induced chirality and applications in environmental protection for Cr(VI) to Cr(III) reduction, in cosmetology as sunscreens, in real-time visualization of cellular processes, in bio-labeling, and in light activated prodrug applications.

Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands

Chemistry of Schiff base (SB) ligands began in 1864 due to the discovery made by Hugo Schiff (Schiff, H., Justus Liebigs Ann. der Chemie 1864, 131 (1), 118-119). However, there is still a vivid interest in coordination compounds based on imine ligands. The aim of this paper is to review the most recent concepts on construction of homo- and hetero-oligonuclear Schiff base coordination compounds narrowed down to the less frequently considered complexes of platinum group metals (PGM). The combination of SB and PGM in oligonuclear entities has several advantages over mononuclear or polynuclear species. Such complexes usually exhibit better electroluminescent, magnetic and/or catalytic properties than mononuclear ones due to intermetallic interactions and frequently have better solubility than polymers. Various construction strategies of oligodentate imine ligands for coordination of PGM are surveyed including simple imine ligands, non-innocent 1,2-diimines, chelating imine systems with additional N/O/S atoms, classic N2O2-compartmental Schiff bases and their modifications resulting in acyclic fused ligands, macrocycles such as calixsalens, metallohelical structures, nano-sized molecular wheels and hybrid materials incorporating mesoionic species. Co-crystallization and formation of metallophilic interactions to extend the mononuclear entities up to oligonuclear coordination species are also discussed.

Near-infrared luminescence and RNA cleavage ability of lanthanide Schiff base complexes derived from N,N'-bis(3-methoxysalicylidene)ethylene-1,2-diamine ligands

A complete series of lanthanide Schiff base salen-type complexes were prepared with trivalent lanthanide ions (Ln³⁺) and the N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine ligand (Ln³⁺=La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺). Three unique crystal structures of La³⁺ and Pr³⁺N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine complexes, with the La³⁺ complex prepared in two different synthetic approaches, are reported, namely a dimeric [La(H₂L)(NO₃)₃]₂ (H₂L=N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine) complex, an asymmetric two-centered [La₂(H₂L)₂(NO₃)₆] complex and a discrete mononuclear [Pr(H₂L)(NO₃)₂(H₂O)₂] complex. For Nd³⁺ and Sm³⁺, an isotypic mononuclear [Nd(H₂L)(NO₃)₃] and 1D polymeric [Sm(H₂L)(NO₃)₃(MeOH)]_n structure was obtained, respectively. The whole series of complexes was tested for their ability to cleave the 20-mer RNA oligonucleotide 5'-AGC-GAU-AAG-AUU-CAU-AUA-UC-3'. Additionally three complexes (Ln³⁺=Nd³⁺, Sm³⁺, Ho³⁺) were tested for the cleavage of the 12-mer RNA oligonucleotide 5'-GCA-CCC-UGU-CAG-3'. A detailed luminescence study was additionally carried out and revealed that the Eu³⁺ complex emitted bright red light upon excitation at both 285.8nm and 394.4nm. The Nd³⁺, Er³⁺, and Yb³⁺ complexes showed strong emission in the near-infrared region after excitation at 380nm.

Metal-promoted synthesis, characterization, crystal structure and RNA cleavage ability of 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) lanthanide complexes

New 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) lanthanide complexes were formed in the metal-induced one-step [1+2] condensation reaction between 2,6-diacetylpyridine and 2-aminobenzoylhydrazide in the presence of lanthanide (La(3+), Pr(3+), Nd(3+), Sm(3+), Eu(3+), Gd(3+), Tb(3+), Dy(3+), Ho(3+), Er(3+), Tm(3+) or Yb(3+)) nitrates as template agents. The analytical and spectral characterizations of all the compounds were correlated with the single crystal X-ray structural determination of Eu(3+), Gd(3+), Tb(3+), Dy(3+) and Er(3+) nitrate complexes. The Eu(3+), Gd(3+), Tb(3+)and Dy(3+) complexes of pentadentate 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) with the N3O2 set of donor atoms display a high and relatively rare coordination number of 11, whereas the Er(3+) ion complex is 9-coordinated, which is consistent with the lanthanide contraction phenomenon. The scission of 21-mer RNA was assessed for Eu(3+), Gd(3+) and Tb(3+) nitrate complexes. Lanthanide complexes not covalently attached to the oligonucleotide are able to cleave RNA at the target site in a sequence-selective or non-selective manner depending on the presence of protecting 12-mer 2'OMe RNA.

Metal‐Containing Polymers

The article provides an overview of the synthesis, properties, and applications of metal‐containing polymers. The past decade has shown an exponential increase in synthetic methods, resulting in metal‐containing polymers, their characterization techniques, and their potential application into a variety of fields, including chemistry, medicine, biotechnology, and more.

Of Chains and Rings: Synthetic Strategies and Theoretical Investigations for Tuning the Structure of Silver Coordination Compounds and Their Applications

Varying the polyethyleneglycol spacer between two (iso)-nicotinic groups of the ligand systems, a large structural variety of silver coordination compounds was obtained, starting with zero-dimensional ring systems, via one-dimensional chains, helices and double-helices to two-dimensional polycatenanes. Theoretical calculations help to understand their formation and allow predictions in some cases. These structures can be tuned by careful design of the ligand, the use of solvent and the counter ions, influencing also other important properties such as light stability and solubility. The latter is important in the context of biomedical applications, using silver compounds as antimicrobial agents.