Ethylenediamine and 1,10-phenanthroline biscyclometallated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine

Biscyclometallated [(M(N∧N))₂(μ-dphpm)](ClO₄)₂ and [(N∧N)Pd(μ-dphpm)Pt(N∧N)]Cl₂ complexes [M = Pd(II), Pt(II); (N∧N) ethylenediamine (En), 1,10-phenanthroline (phen); dphpm² — bisdeprotonated form of 4,6-diphenylpyrimidine)] have been characterized by the ¹H NMR, electronic absorption and emission spectroscopy, and also cyclic voltammetry methods. The lowest unoccupied molecular orbital (LUMO) of biscyclometallated complexes with ethylenediamine, responsible for low-energy photo- and electro-stimulated processes irrespective of the metal nature, is assigned to the π* orbital mainly localized on the pyrimidine part of the bridging ligand. In the case of complexes with phenanthroline chelating ligands, the replacement of one or two palladium metal centers [{Pd(phen)}₂(μ-dphpm)]²⁺ by platinum centers changes the LUMO nature of the complexes for the π* orbital mainly localized on the peripheral metal-complex fragment {Pt(phen)}.