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This is an example of a dissociative mechanism, where an 18 e − complex loses a CO ligand, making a 16 e − intermediate, and a final complex of 18 e − results from an incoming ligand inserting in place of the CO. This mechanism resembles the S N 1 mechanism in organic chemistry, and applies to coordination compounds as well. [6] Figure 1.
The term "octahedral" is used somewhat loosely by chemists, focusing on the geometry of the bonds to the central atom and not considering differences among the ligands themselves. For example, [Co(NH 3) 6] 3+, which is not octahedral in the mathematical sense due to the orientation of the N−H bonds, is referred to as octahedral. [2]
Coordination complexes with octahedral or square planar geometries can also exhibit cis-trans isomerism. The two isomeric complexes, cisplatin and transplatin For example, there are two isomers of square planar Pt(NH 3 ) 2 Cl 2 , as explained by Alfred Werner in 1893.
In organic structural chemistry, the configuration of a double bond can be described with cis and trans, in case it has a simple substitution pattern with only two residues. The position of two residues relative to one another at different points in a ring system or a larger molecule can also be described with cis and trans if the structure's ...
The ligand can bend so that one donor atom is at the pole and the remaining three are on the equator of the central atom. This is called cis-β (beta). The remaining octahedral positions are cis (adjacent) to each other. The triangles of coordinating atoms and the central atom have two coplanar atoms, and one perpendicular atom.
For example, in the rock salt ionic structure each sodium atom has six near neighbour chloride ions in an octahedral geometry and each chloride has similarly six near neighbour sodium ions in an octahedral geometry. In metals with the body centred cubic (bcc) structure each atom has eight nearest neighbours in a cubic geometry.
The rate of reductive elimination is greatly influenced by the geometry of the metal complex. In octahedral complexes, reductive elimination can be very slow from the coordinatively saturated center; and often, reductive elimination only proceeds via a dissociative mechanism, where a ligand must initially dissociate to make a five-coordinate ...
Molybdenum hexacarbonyl is a popular reagent in academic research. [6]One or more CO ligands can be displaced by other ligands. [7] Mo(CO) 6, [Mo(CO) 3 (MeCN) 3], and related derivatives are employed as catalysts in organic synthesis for example, alkyne metathesis and the Pauson–Khand reaction.