C ptcl 2 co 2 or nico 2 pph 3 2 the ni complex is in

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c) PtCl 2 (CO) 2 or Ni(CO) 2 (PPh 3 ) 2 The Ni complex is in the zero oxidation state ( d 10 ) and has moderately good donor PPh 3 ligands, which will make it more electron-rich and have the lower CO stretching frequency. The Pt complex is more electron- deficient due to the poorly donating Cl ligands, the +2 oxidation state, and d 8 electron configuration. Although Pt is less electronegative than Ni and as a 3 rd row metal will bind more strongly to the CO, but these are relatively minor factors compared to the stronger ligand effects. d) [Co(CO) 4 ] or [Fe(CO) 4 ] 2 The Co complex is less electron-rich due to the fact that it is more electronegative, and thus willing to hang onto its d electron density and not -backbond to the CO ligands. Secondly it only has a single anionic charge while the Fe complex is dianionic and less electronegative. This will overload the Fe complex and make it considerably more electron-rich. The CO stretching frequency for each complex is given in your notes. e) MnF(CO) 5 or WI 2 (CO) 4 The Mn complex is less electron-rich due to the fact that it has a very poorly donating F ligand and one extra CO ligand relative to the W complex. Secondly, it is more electronegative and will hang onto its d electron density and not -backbond to the CO ligands as well. The iodide donors on the tungsten complex are considerably stronger donors relative to the fluoride, so the tungsten complex is more electron-rich and will have the lower CO stretching frequency.

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