Reference no: EM132393365 , Length: 3 Pages
Assignment -
The molecule in question is W(CO)3(PR3)2(H2).
1. Consider only the η2-M-H2 fragment. If the fragment were a stand-alone discrete molecule, calculate the number of fundamental vibrations one would expect in the infrared spectrum. Identify the translational and rotational modes. Give a symmetry label and a description to each fundamental vibrational mode. Draw each vibrational mode. Use the same axes as set-up for the full molecule.
Note: Use the approximations that the P ligands can rotate and are viewed as spherical blobs, and where the H2 ligand lies approximately parallel to the P-W-P axes as shown in attached file.
2. When the fragment is returned to the trans molecule it turns out there should be 6 fundamental vibrations associated with the η2-MH2 fragments. One method proposed to analyze the nature of these vibrations is to consider only the motions of the H-H fragment (without the metal) first outside of, and then when placed back into the full molecule. The H2 diatomic should have 3N modes of motion and 3N-5 vibrations (so only 1 vibration in the free H2: the H-H stretch). The free H2 molecule has 3 translations: x, y and z translations, and two rotations; a unique Rz rotation (along the H-H bond) and a Ry and Rz rotation that are degenerate in the free H2 molecule (but not degenerate when the H2 is placed back in the full molecule). Note that we are using the previously assigned axis system (with the x axis containing both H atoms - do not create a new coordinate system since we are putting the H2 back into the molecule). If you now place the H-H in the molecule and allow the H2 fragment to vibrate, rotate and translate within the molecule, determine if each type of motion gives rise to a molecular motion within the full molecule that could be depicted as a vibration. Note that the H-H stretch is a given. It is one of the 6 fundamental vibrations associated with the H2 fragment. Now look for the other 5 vibrations.
Use this method to test every motion of free H2 when it is placed back into the full molecule to determine if you can find 4 more motions that could be described as vibrations within the full molecule (and note: all of these motions should be characteristically sensitive to deuterium (heavy atom) labeling!).
Summarize your answer by listing the vibrations in the table (see attached file).
Attachment:- Assignment File - Inorganic Work.rar