<p>We report the synthesis and characterization of a
series of cationic, neutral and anionic dicopper(I) complexes featuring a <i>µ</i>-mesityl ligand and a
naphthyridine-derived PNNP expanded pincer ligand. Structural characterization
showed that the protonation state of the dinucleating ligand has a pronounced
effect on the bending and tilting of the <i>µ</i>-mesityl
ligand. DFT calculations indicate that the varying orientations of the <i>µ</i>-mesityl ligand are inherent due to
changes in electronic structure rather than crystal packing effects. NBO
analysis reveals how the interactions that contribute to the 3-center
2-electron bond between the <i>µ</i>-mesityl
ligand and the dicopper core change for the various degrees of observed bending
and tilting. </p>