This project aims ultimately at understanding the properties of magnetic molecules adsorbed on surfaces. However, due to lack of structural information on surface adsorbed molecules, detailed understanding of crystal-field perturbations in molecules is most reliably obtained in the bulk by chemical modification. The main focus is on the mononuclear erbium complex; Er(trensal) exhibiting three-fold crystallographic symmetry and single-ion magnet (SIM) behaviour and ee have recently proven the feasibility of INS to study crystal-field effects in SIMs (Pedersen et al. Chem. Sci., 2014, ASAP). The bonding in lanthanide compounds is largely ionic due to the shielded nature of the 4f orbitals. However, covalent bonding is important for the magnetic properties and even pi interactions may provide a sizable contribution to the magnetic anisotropy. We intend to expand our treatment of crystal-field spectroscopy on SIMs to quantify the extend of pi interactions in lanthanide systems. A carefully chosen system resembling the pristine Er(trensal) SIM but crystallizing in a different trigonal space group with different tilting planes of the pi interaction pathways will be studied.