Di- and Tetranuclear Metal Complexes with Phenoxo Bridges: Synthesis, Structures, and Photoluminescent and Electroluminescent Properties

Abstract

Dinuclear and tetranuclear copper 2,6-bis(2-hydroxyphenyl)pyridine (H(2)L) complexes Cu2(L)2(py)2 (1) and Cu4(L)4(DMF) (2) were synthesized. The complexes 1 and 2 were characterized by elemental analyses, mass spectrometry, and single-crystal X-ray diffraction analyses. 1 crystallizes in the monoclinic space group P2(1)/n with a = 13.330(2) Angstroms, b = 9.361(1) Angstroms, c = 14.676(1) Angstroms, beta = 100.94(1) degrees, V = 1798.1(3) Angstroms(3), and Z = 2. 2 crystallizes in the monoclinic space group P2(1)/n with a = 13.360(1) Angstroms, b = 14.884(1) Angstroms, c = 15.462(2) Angstroms, beta = 97.50(4) degrees, V = 3048.4(1) Angstroms(3), and Z = 2. Tetranuclear zinc complex Zn4(L)4(py)4 (3) was prepared and characterized by X-ray diffraction. 3 crystallizes in the triclinic space group P with a = 13.770(1) Angstroms, b = 15.465(1) A, c = 16.409(2) Angstroms, alpha = 88.877(9) degrees, beta = 88.035(4) degrees, gamma = 82.956(3) degrees, V = 3465.6(5) Angstroms(3), and Z = 2. The di- and tetranuclear complexes 1-3contain phenoxo bridges. 1 is a dinuclear complex with two Cu(II) centers, two py ligands, and two L ligands, and each L ligand donates its pyridyl ring and one of the phenolate groups to one metal and shares the other phenolate group between both metals, affording a Cu(2)(mu-O)(2) core. 2, in contrast, is a tetranuclear complex with four Cu(II) centers and four L ligands. Two of the L ligands have the same coordination mode as 1, and the other two L ligands donate their pyridyl rings to one metal and share both phenolate groups between four metals, resulting in three four-membered Cu2(mu-O)2 rings, which joined each other and showed great distortion from planarity. 3 is a tetranuclear complex with four Zn(II) centers, four pyridine ligands, and four L ligands, and the L ligands have the same coordination modes as those of 2. Single-crystal X-ray analysis showed that hydrogen-bonding and pi-pi stacking interactions exist in complexes 1 and 2 resulting in two- and three-dimensional molecular arrangements, and the parallel arrangement of the ligand in the crystal of complex 3 resulted in a close inter- and intramolecular pi-pi interactions. Investigation of the crystals, as well as an amorphous thin film and powder of 3, by photoluminescence (PL) allowed the effect of the molecular packing on the emission properties to be elucidated. Furthermore, the electroluminescent (EL) properties of 3 were examined by fabricating a multilayer device with structure of [ITO/NPB/(ZnL)(n)/Alq3/LiF/Al] (NPB = N,N'-bis(alpha-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine, Alq3 = tris(8-hydroxyquinolinato)aluminum).