Briefly explain the role of IR spectroscopy in structural determination of inorg

Question

Briefly explain the role of IR spectroscopy in structural determination of inorganic compounds. Resonance structure of Urea is as shown below. The IR spectrum of free urea has absorptions at 3500 cm^-1 and 3350 cm^-1 (v(NH_2), 1683 cm^-1 (v(CN), and 1471 cm^-1 (v(CN). Urea can bond to metals either through N or O as donor atoms. When urea binds to metal through N-donor atom, the contribution from first resonance form on the left decreases. In the IR spectrum of [Pt(urea)_6Cl_2 bands at 3390 cm^-1, 3290 cm.^-1, 3130 cm^-1, 3030 cm^-1 1725 cm^-1 and 1395 cm^-1 are assigned to the metal bound urea. What do these data suggest about the binding of metal to urea. Is it a Pt-N bond or a Pt-O bond?

Explanation / Answer

IR spectrum of [Pt(urea)6Cl2] indicate that this complex is Pt-N bond.

The cordination take place at nitrogen of amide group, positvely charged metal ion satabilizes the loan pair of electron on nitrogen atom; the NCO group now not in its polar resonance form, while the double bond character of the CO bond increases, resulting in an decrease of the CN stretching frequency with a simultaneous decrease in the CO stretching frequency.

V (3390, 3290 cm-1) as NH2 and OH from H2O

V( 3130, 3030 cm-1) as NH2

V( 1725 cm-1) as C=O

V( 1395 cm-1) as C-N

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