The expected number of co bands in the IR spectra of fac-[Mo(PPh₃)₂(CO)₃] and trans-[Mo(PPh₃)₂(CO)₄] are… · ABC26IN0280
Subject: Inorganic Chemistry · Chapter: Organometallic Compounds · Topic: Organometallic Compounds – General · Exam: CSIR NET 2019 · Marks: 2 · Difficulty: Medium
The expected number of co bands in the IR spectra of fac-$\mathrm{[Mo(PPh_3)_2(CO)_3]}$ and trans-$\mathrm{[Mo(PPh_3)_2(CO)_4]}$ are, respectively
(a)one and one
(b)Two and two
(c)two and one
(d)three and one
Answer
Answer: C ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
The descriptor fac applies to an octahedral MA₃B₃ complex, so the printed fac-[Mo(PPh₃)₂(CO)₃] must be read as fac-[Mo(PPh₃)₃(CO)₃] (a misprint in the source).
fac-[Mo(PPh₃)₃(CO)₃] has C₃v symmetry: the three CO stretches span A₁ + E, both IR-active, so two ν(CO) bands.
trans-[Mo(PPh₃)₂(CO)₄] has D₄h symmetry (four CO in one plane): the stretches span A₁g + B₁g + Eu, and only Eu is IR-active, so one band.