Influence of phenyl ring substituents in the cyclometallation of Schiff base ligands: crystal and molecular structures of [Pd-{3,4-(OCH2O)C6H2C(H)N(Cy)-C2,N}(μ-O2CMe)]2 and [Pd-{3,4-(OCH2CH2O)C6H2C(H)N(Cy)-C6,N}(μ-O2CMe)]2