Metal isotope effect on metal-ligand vibrations—VIII

Speciation Analysis of Metals and Metalloids by Surface Enhanced Raman Spectroscopy

The presence of metalloids and heavy metals in the environment is of critical concern due to their toxicological impacts. However, not all metallic species have the same risk level. Specifically, the physical, chemical, and isotopic speciation of the metal(loids) dictate their metabolism, toxicity, and environmental fate. As such, speciation analysis is critical for environmental monitoring and risk assessment. In the past two decades, surface-enhanced Raman spectroscopy (SERS) has seen significant developments regarding trace metal(loid) sensing due to its ultrahigh sensitivity, readiness for in situ real-time applications, and cost-effectiveness. However, the speciation of metal(loid)s has not been accounted for in the design and application of SERS sensors. In this Perspective, we examine the potential of SERS for metal(loid) speciation analysis and highlight the advantages, progress, opportunities, and challenges of this application.

Synthesis, characterization, and crystal structures of novel oligomeric Zn(II) and Cd(II) complexes with N,N′-dimethyl-2,2′-biimidazole

Zn(II) and Cd(II) complexes with N,N′-dimethyl-2,2′-biimidazole (Me2biim) were synthesized and characterized by IR spectroscopy and by X-ray crystallographic methods. The reaction of zinc perchlorate with Me2biim produced the dinuclear compound [(Me2biim)Zn(µ-Me2biim)3Zn(Me2biim)](ClO4)4, containing two monodentate and three bridging Me2biim ligands bonded to Zn atoms in a distorted tetrahedral environment. A related neutral (NO3)2Cd(µ-Me2biim)3Cd(NO3)2 complex, containing only bridging Me2biim ligands, was also synthesized, in which the distorted octahedral coordination of each Cd atom is completed by one monodentate and one bidentate nitrato ligand. Two ionic trinuclear Cd compounds were also obtained, which include two sets of three bridging Me2biim ligands connecting a central Cd atom to two terminal Cd centers. An extra Me2biim ligand is chelated to each terminal metal, and the sixth coordination site is occupied by water molecules in the symmetric [(Me2biim)(H2O)Cd(µ-Me2biim)3Cd(µ-Me2biim)3Cd(H2O)(Me2biim)](ClO4)6 complex, whereas the aqua ligand is replaced by methanol at one of the terminal units in the non-symmetric [(Me2biim)(H2O)Cd(µ-Me2biim)3Cd(µ-Me2biim)3Cd(CH3OH)(Me2biim)](ClO4)6 compound. In the chelating ligands, dihedral angles of ~38° between the two imidazole rings reduce repulsion between the N-methyl groups, but considerable strain remains, as evidenced from one of the Cd–N bonds being much longer than the other. In the various compounds, dihedral angles of 60–80° are found between the imidazole rings in the bridging ligands, and intramolecular inter-ligand π–π stacking contributes to stabilization.Key words: zinc, cadmium, dimethylbiimidazole, crystal structure, dinuclear, trinuclear.