Abstract Here we report results of orientation dependent nuclear inelastic scattering (NIS) experiments on a single crystal of a chemical ferrous iron complex performed at T = 10 K. For that purpose, we have constructed a sample holder which is equipped with a magnetic coupling to accommodate single crystal loops as used in protein crystallography. The sample holder is compatible with the sample rod of a helium cryostat at beamline P01, PETRA III, DESY Hamburg, which allows NIS experiments down to liquid He temperatures and below. For our experiments we chose a 57 Fe enriched single crystal of the compound Fe II (b(bdpa))(PF 6 ) 2 , with (b(bdpa)) = N, N‘-bis(benzyl)-N, N’-bis(2-pyridylmethyl)-6,6’-bis(aminomethyl)-2,2’-bipyridine). Crystals of this complex have unit cells containing two crystallographically independent molecular sites. Our single crystal NIS experiments show that the two irons of the unit cell are in their low spin (S = 0) state at 10 K. This is in contradiction with previous findings (Brady at al. Inorg. Chem. 2004, 43, 14, 4289–4299) which show significant residual high spin (S = 2) contributions up to 25% as obtained from Mössbauer Spectroscopy and susceptibility measurements at room temperature.
Tummeley et al. (Wed,) studied this question.