previously. We use a combination of magnetometry and complete active space self-consistent field spin-orbit (CASSCF-SO) calculations to disentangle the influence of equatorial ligand binding on the SMM behavior of the halobenzene-bound adducts compared to the parent CIP and SIP complexes. We find extremely slow and divergent relaxation times for the monohalobenzene adducts at low temperatures, and by comparison to a magnetically diluted sample of the fluorobenzene adduct we identify unusual phonon bottleneck behavior in zero field.