Cadmium: Coordination Chemistry

Abstract

The coordinative behavior of cadmium(II) is typical of a soft acid. Evidence of this fact is its strong interactions with S 2 − and HS − groups leading to the formation of highly stable complexes. Interactions with ligands containing oxygen‐donor groups are also well known. The chemistry of Cd II shows versatile coordination abilities, giving structures ranging from simple complexes to 1D, 2D, and 3D polymeric architectures. These polymers exhibit interesting physical properties. Cd II is able to substitute Zn II in the active site of several Zn‐enzymes and to interfere with the metabolism of Ca II . This is why a strong interest has been devoted in the past decade to the coordination chemistry of cadmium. The coordinative behavior of the cadmium(II) ion resembles that of mercury(II) and, in a lesser extent, of zinc(II). The main coordination numbers observed for Cd II are 4, 5, and 6. Owing to the larger size, Cd II assumes coordination number 6 more easily than Zn II . In CdMe 2 and dihalides in gas phase, Cd II only binds to two ligands, but in solid and solution phase, the coordination number is higher than 2. Coordination number 3 characterizes CdX 3 − (X = halide) in organic media; however, in aqueous solution, CdBr 3 − is pyramidal owing to the binding of one or more water molecules. Coordination numbers higher than 3 are observed in solid MCdX 3 . In aqueous solution, CdX 4 2 − anions are tetracoordinated. Most CdX 2 L 2 complexes show a coordination number higher than 4, but a distorted tetrahedral geometry is found in CdX 2 L 2 when L is a P‐ or S‐donor. Cd 2+ is found to be five coordinated in CdCl 5 3 − . A very large number of Cd compounds are six coordinated, for example, [Cd(H 2 O) 6 ] 2+ , [Cd(acac) 2 ], and [Cd(acac) 3 ] − (acac = acetylacetonate) have a CdO 6 core. Six‐coordinated CdN 6 ions are formed with mono‐ and bidentate ligands such as imidazole or ethane‐1,2‐diamine. In the solid state, CdX 2 compounds are six coordinated. Halide adducts of the type CdX 4 L 2 are common; halogen bridging leads to an approximately octahedral Cd II for Cl − and Br − , but I − gives either four and five‐coordinated Cd II . A few seven‐coordinated compounds are known: in the solid state, each Cd II ion in [Cd(H 2 O)(CH 3 OC 6 H 4 COO) 2 ] n is seven coordinated in a distorted pentagonal bipyramidal geometry. Eight coordination is rare. CdF 2 contains a CdF 8 core in a fluorite structure. In Cd(NO) 3 ·4H 2 O, the four water molecules are square planar and bidentate NO 3 − anions lie above and below this plane.

Tandem mass spectroscopy as a tool for investigation of complexes of PNP‐lariat ether derivative with metal ions

“…It is probably connected with the size of the metal ion (they are nearly equal or larger then silver ion, and hence, they are perching over the macrocyclic ring, as it was observed in the case of silver complexes, giving the opportunity to attaching other ligands—water molecules to the metal ion). Furthermore, the preferred coordination number of the investigated metal ions (4 or 6) gives additional assumption for such behavior. During the measurement conditions in the ESI‐MS experiments, the sodium adducts are usually present on the spectra.…”

The Use of a Two-Dimensional Electrical Resistivity Tomography (2D-ERT) as a Technique for Cadmium Determination in Cacao Crop Soils

“…We highlighted the use of 2D-ERT to assess both the horizontal and vertical distributions of Cd in geomorphs and their locations underground. The accuracy of the 2D-ERT technique (R 2 = 0.84) to describe Cd distribution with Cd counts by spectrometry is also highlighted, even when no (phyto)available Cd was described [44].…”

“…With exception of the DGT method [38], the mentioned below techniques have not yet been applied in cacao farm soils to our knowledge. Cd has an excellent electric conductivity [44]. Therefore, the study of Cd distribution in soils under cacao trees requires non-destructive and non-invasive methods to assess its presence and its relationship with mobile fractions of Cd in cacao beans.…”

Synthesis and Single Crystal Structure Characterization of Dinuclear and Polymeric Mixed‐ligand Coordination Compounds of Zinc(II) and Cadmium(II) with the Bridging Ligand 1,2‐Bis(pyridin‐4‐ylmethylene)hydrazine

“…Generally, coordination numbers of Cd 2+ and Zn 2+ in coordination compounds are four, five, and six. [ 52 ] In this work Cd 2+ and Zn 2+ ions have five and six coordinated geometries with octahedral, trigonal bipyramid and square pyramid.…”