Inelastic neutron scattering study of the anisotropic S=1 spin chain [Ni(HF2)(3-Clpyridine)4]BF4

[Ni(HF2)(3-Clpyridine)(4)]BF4 (NBCT) is a one-dimensional, S = 1 spin chain material that shows no magnetic neutron Bragg peaks down to temperatures of 0.1 K. Previous work identified NBCT as being in the Haldane phase and near a quantum phase transition as a function of D/J to the large-D quantum paramagnet phase (QPM), where D is the axial single-ion anisotropy and J is the intrachain superexchange. Herein, inelastic neutron scattering results are presented on partially deuterated, B-11-enriched NBCT polycrystalline samples in zero magnetic field and down to temperatures of 0.3 K. Comparison to density matrix renormalization group calculations yields D/J = 1.51 and a significant rhombic single-ion anisotropy E (E/D approximate to 0.03, E/J approximate to 0.05). These D, J, and E values place NBCT in the large-D QPM phase but precipitously near a quantum phase transition to a long-range ordered phase.