Metal-ligand Jt bonding

In liquid ammonia, hexacyanochromates(II) can be reduced to the diamagnetic chromium(O) complexes M6[Cr(CN)6] by the appropriate alkali metal. The K salt was earlier obtained by reduction of K3[Cr(CN)6], Greater metal-ligand jt bonding is presumably responsible for the lower CN stretching frequencies of M6[Cr(CN)6]. The potassium salt is oxidized to K3[Cr(CN)6] by ammonium cyanide in liquid ammonia (equation l).12... 

The position of acac ion in the spectrochemical series involves weaker metal ligand jT-bonding (close to water) than the relatively high jt-jt transition energies would suggest. This assessment is based on Hiickel s LCAO theory. In MO levels of the acac ion the jt3 orbital is occupied and the 7t4 unoccupied antibonding MO is energetically suitable for overlap with the metal rf-orbital. The reason is that both donor-acceptor... 

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