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The system most often studied for the cis effect is an octahedral complex M(CO) 5 X where X is the ligand that will labilize a CO ligand cis to it. Unlike the trans effect, which is most often observed in 4-coordinate square planar complexes, the cis effect is observed in 6-coordinate octahedral transition metal complexes.
For ML a 4 L b 2, two isomers exist.These isomers of ML a 4 L b 2 are cis, if the L b ligands are mutually adjacent, and trans, if the L b groups are situated 180° to each other. It was the analysis of such complexes that led Alfred Werner to the 1913 Nobel Prize–winning postulation of octahedral complexes.
Very often, cis–trans stereoisomers contain double bonds or ring structures. In both cases the rotation of bonds is restricted or prevented. [4] When the substituent groups are oriented in the same direction, the diastereomer is referred to as cis, whereas when the substituents are oriented in opposing directions, the diastereomer is referred to as trans.
The descriptors cis (Latin, on this side of) [2] and trans (Latin, over, beyond) [3] are used in various contexts for the description of chemical configurations: [4] [5] 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.
In an octahedral complex, the molecular orbitals created by coordination can be seen as resulting from the donation of two electrons by each of six σ-donor ligands to the d-orbitals on the metal. In octahedral complexes, ligands approach along the x -, y - and z -axes, so their σ-symmetry orbitals form bonding and anti-bonding combinations ...
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 octahedral mono- and dicationic aquo complexes, these exchange processes occur via an interchange pathway that has more or less dissociative character. [4] Rates vary by a factor of 10 18, [Ir(H 2 O) 6] 3+ being the slowest and [Na(H 2 O) 6] + being one of the fastest for octahedral complexes. Charge has a significant influence on these ...
A few octahedral homoleptic pyridine complexes are known. These complex cations are found in the salts [Ru(py) 6]Fe 4 (CO) 13 and [Ru(py) 6](BF 4) 2. [3] [4] Some compounds with the stoichiometry M(py) 6 (ClO 4) 2 have been reformulated as [M(py) 4 (ClO 4) 2]. (py) 2 [5] A common family of pyridine complexes are of the type [MCl 2 (py) 4] n+ ...