Natural orbital function vibrational frequencies

Natural orbital functional vibrational frequencies. Experimental vibrational frequencies from Ref. [90]. 

The coupling constants Jp M are one of the several easily obtainable physical parameters of phosphorus co-ordination compounds, but they are especially important because they are essentially a property of a particular bond of the complex. Other properties, such as the dipole moment or a vibration frequency, often involve substantial contributions from other bonds within the complex, and thus require some estimate of these relative contributions before the property of an individual bond is known. As a means of investigating the nature of P—bonds, the coupling constants also have an advantage over most other parameters in that an approximate equation for their magnitude can be derived from molecular orbital theory, which principally involves terms associated with the wave function of the P—bond. 

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