Polarized Raman spectra of single-crystal barium nitroprusside trihydrate, Ba[Fe(CN)5NO]·3H2O

The room‐temperature polarized Raman scattering of single‐crystal Ba [Fe(CN)5NO] · 3H2O, space group Pbcm (D 112h, No. 57), in the 2200–10 cm−1 spectral range, and a factor group analysis of the nitroprusside anion vibrational modes are presented. The near parallelism between the anion NCFeNO axis and a crystallographic axis facilitates the interpretation of the spectra. The data obtained complement already existing IR studies and the two series of results together provide reference information for the understanding of the vibrational behaviour of the recently reported electronically excited metastable states of the anion. The Raman data confirm the existence of a relatively large correlation (Davydov) splitting between NO stretching modes due to vibrational coupling between neighbouring nitrosyl groups in the lattice.