High frequency EPR investigations have been undertaken to gain insight into the spin environment of a novel pentanuclear FeIII cluster, [Fe 5O2(OMe)2(Bta)4(BtaH)/(MeOH) 5Cl5] (Fe5Bta). The elongated, centered ferric tetrahedron contains five FeIII ions with a S = 15/2 ground spin state. Variable temperature EPR suggests that the first paramagnetic excited spin state is low lying. Employing high frequencies and fields in the EPR experiments allows for resolution of g anisotropy of the FeIII centers. We therefore are able to determine the g value of the FeIII ion precisely.