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Representative d-orbital splitting diagrams for square planar complexes featuring σ-donor (left) and σ+π-donor (right) ligands. A general d-orbital splitting diagram for square planar (D 4h) transition metal complexes can be derived from the general octahedral (O h) splitting diagram, in which the d z 2 and the d x 2 −y 2 orbitals are degenerate and higher in energy than the degenerate ...
A V 3+ complex will have a larger Δ than a V 2+ complex for a given set of ligands, as the difference in charge density allows the ligands to be closer to a V 3+ ion than to a V 2+ ion. The smaller distance between the ligand and the metal ion results in a larger Δ, because the ligand and metal electrons are closer together and therefore ...
Square planar complexes of the type [Pt(bipy) 2] 2+ react with nucleophiles because of the steric clash between the 6,6' positions between the pair of bipy ligands. This clash is indicated by the bowing of the pyridyl rings out of the plane defined by PtN 4 .
An unusual route to thiocyanate complexes involves oxidative addition of thiocyanogen to low valent metal complexes: [21] Ru(PPh 3) 2 (CO) 3 + (SCN) 2 → Ru(NCS) 2 (PPh 3) 2 (CO) 2 + CO, where Ph = C 6 H 5. Even though the reaction involves cleavage of the S-S bond in thiocyanogen, the product is the Ru-NCS linkage isomer.
Low-spin [Fe(NO 2) 6] 3− crystal field diagram. The Δ splitting of the d orbitals plays an important role in the electron spin state of a coordination complex. Three factors affect Δ: the period (row in periodic table) of the metal ion, the charge of the metal ion, and the field strength of the complex's ligands as described by the spectrochemical series.
Complexes which are d 8 high-spin are usually octahedral (or tetrahedral) while low-spin d 8 complexes are generally 16-electron square planar complexes. For first row transition metal complexes such as Ni 2+ and Cu + also form five-coordinate 18-electron species which vary from square pyramidal to trigonal bipyramidal.
At picture below is shown the splitting of the d subshell in low-spin square-planar complexes. Examples are especially prevalent for derivatives of the cobalt and nickel triads. Such compounds are typically square-planar. The most famous example is Vaska's complex (IrCl(CO)(PPh 3) 2), [PtCl 4] 2−, and Zeise's salt [PtCl 3 (η 2-C 2 H 4)] − ...
Examples of associative mechanisms are commonly found in the chemistry of 16e square planar metal complexes, e.g. Vaska's complex and tetrachloroplatinate. These compounds (MX 4) bind the incoming (substituting) ligand Y to form pentacoordinate intermediates MX 4 Y that in a subsequent step dissociates one of their ligands.