Synthesis, structures and characterization of a series of Cu(I)-diimine complexes with labile N,N′-bis((diphenylphosphino)methyl)naphthalene-1,5-diamine: diverse structures directed by π–π stacking interactions

Five complexes [Cu2(phen)2(dpna)](ClO4)2 (1), [Cu2(dmp)2(dpna)](ClO4)2 (2), {[Cu(phen)(dpna)](ClO4)}n (3), [Cu2(pz)(dpna)](ClO4)2 (4) and [Cu2(pz)(dpna)2](ClO4)2 (5) (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, pz = pyrazine, dpna = N,N′-bis((diphenylphosphino)methyl)naphthalene-1,5-diamine) were rationally synthesized and characterized by elemental analysis, IR, MS and X-ray diffraction analysis. The building of these structures is directed by intramolecular π–π stacking interactions between an electron-poor diimine ring and an electron-rich naphthalene ring based on the electron complementarity of π-systems, while the lability of dpna can meet the needs of their conformations. In 1, 2 and 3, dpna takes a trans coordination mode to bridge two Cu+. 1 and 2 are discrete dinuclear complexes with a three-layered π-stacking conformation in which the electron-rich naphthalene ring is sandwiched by two electron-poor diimine rings. 3 is a polymer in which the electron-poor phen ring and the electron-rich naphthalene ring are sandwiched alternately by one another, resulting in a π-stacked column. In 4 and 5, dpna acts in a cis coordination mode to bridge two Cu+. 4 is a dinuclear complex with two-layered π-stacking between naphthalene and pyrazine rings. 5 is a three-layered π-stacking conformation in which the electron-poor pyrazine ring is sandwiched by two electron-rich naphthalene rings. The π-sandwich mode in 5 is contrary to that in 1 and 2.