Sphere of the complexes and their stability constants in acetone medium. Main bond (Å) and angles (°) for the coordination Region and absorbances at fixed wavelengths have been gathered as describedĮlsewhere 6. Measurements of diffraction intensities, solution and refinement of theĭiffraction data were already described 4, 5. Equipment used for collection of X-ray diffraction data, Solid complexes, appropriate for X-ray examination were prepared as previouslyĭescribed 3. The present article deals with X-ray data for the solid complexes of general formula CoCl 2L 2, where L = triphenylphosphine oxide (TPPO), benzyldiphenylphosphine oxide (BDPPO), dibenzylphenylphosphine oxide (DBPPO) or tribenzylphosphine oxide (TBPO) as well as with formation constants of these complexes in acetone medium, at 25 ☌. Furthermore, the goal stated by the authors 2 namely, to establish correlations between solid structures and their corresponding thermodynamic data in solution was certainly not achieved. However, the work is quite restricted (explicitly, only two solid complexes – and these are not directly comparable – are considered). Very recently, an attempt to correlate bond lengths (in solids) and stability constants (in solution) involving organometallic complexes has been published 2. So far as we know, correlations between X-ray structural data for the solid complexes and their stability constants in solution have not been reported. In some cases, very good correlations were found 1 on the other hand, complexes comprising the same oxygen donors showed no correlation at all 1. Six coordination is normally more easily achieved using chelates such as edta.ĭepending on the cation, 2- displays structures ranging from square-planar (NH 4 +) to almost tetrahedral (Cs +), the former being usually green and the latter orange in colour.įind an alternative 'reverse' approach suggested here.First attempts made to correlate variations in bands assigned as carbonyl stretching frequencies in the infrared region for solid metal ion complexes with the stability constants of these same complexes in solution date back to early 1950s. Hexammines can be made from liquid ammonia and stored in an atmosphere of ammonia. These are relatively easily to prepare and isolate. This is the normally accepted structure for tetrammines. (You will have to refer to advanced texts on the Jahn-Teller effect to explain.) The usual result is an elongation of the octahedron (four + two) coordination with complete loss of the axial ligands resulting in square-planar complexes. However, the distinction between square-planar and tetragonally-distorted octahedral coordination is not easily made. 2- + 4NH 3 → 2+ + 4Cl -Ĭopper can have coordination numbers of four, five and six, though the shape is often described as square-planar. When concentrated ammonia is added, further ligand exchange occurs: In this case, the coordination number of the copper changes from six to four.
The empty 4s and 4p orbitals are used to accept a lone pair of electrons from each chloride ion. When concentrated hydrochloric acid is added, ligand exchange occurs: When copper sulfate dissolves in water, the water molecules act as ligands, producing the complex ion 2+. To form a Cu 2+ ion a copper atom loses the 4s electron and one of the 3d electrons, leaving it with the electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 9. By donating a pair of electrons, ligands act as Lewis bases.Ĭopper has the electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1.
These molecules or ions are called ligands and all have the same common feature: a pair of non-bonding (lone pair) electrons. These can be considered to be attached to the central ion by coordinate (dative covalent) bonds.
1 A complex ion has a metal ion at its centre with several other molecules or ions surrounding it. However, it is best used as an opening for complex chemistry. This demonstration can be used as an introduction to reversible reactions for ages 14-16, equilibrium at post-16, and as an example of entropy changes in solution.
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