The parameters of the interacting boson model are calculated in a shell model framework, using a generalized seniority basis. The effect of the neutron-proton interaction on the s- and d-boson structure is explicitly considered. The renormalization due to the truncation of the full fermion space to the S-D subspace is considered by taking the effects of the G-pair state into account using perturbation theory. It is found that this effects mainly the single boson energies and introduces a Majorana force that favors states symmetric in neutron and proton degrees of freedom over antisymmetric ones.