Blue luminescent zinc (II) complexes with polypyridylamine ligands: crystal structures and luminescence properties

摘要

A series of blue luminescent zinc (II) complexes, [Zn(dpa)X_2] [dpa = di-2-pyridylamine, X = OAc 1a, Cl 1b, CN 1c or 4-MeC_6H_4S 1d], [Zn(dpa)_2] [CF_3SO_3]_2 2, [Zn(tpda)X_2][tpda = 2, 6-bis(2-pyridylamino) pyridine, X = OAc 3a or Cl 3b] and [Zn(tpda)(CF_3SO_3)_2] 4 has been prepared. Their molecular structures, except complex 4, have been established by X-ray crystallography. In the crystal lattice of 2 the [Zn(dpa)_2]~(2+) cations and CF_3SO_3~- anions are disposed in pairs via intermolecular hydrogen bonds [N(2)...O(2) 2.865 (4) A]. The crystal packing of [Zn(dpa)(OAc)_2] 1a revealed that two adjacent molecules associate in pairs through intermolecular hydrogen bonding [N(2)...O(4') 2.816 (3)A]. However, the crystal lattice of its tpda derivative 3a shows that the molecules are linked by extensive intermolecular hydrogen bonding between the amino groups and the acetate ligands [N(2)...O(2') 2.805 (3) and N(4)...O(4') 2.860 (3)A] resulting in an interlocking hydrogen bond network. Polymeric one-dimensional tapes are generated through extended #pi#-#pi# stacking interactions between the molecules of [Zn(dpa)(4-MeC_6H_4S)_2] 1d, and the thiolate groups are aligned in an all-anti conformation along the metal chain. In the case of [Zn(dpa)(CN)_2] 1c, co-operative intermolecular hydrogen bonds and aromatic #pi#-#pi# interactions in its solid state lead to a supramolecular two-dimensional sheet. All the zinc(II) complexes display high energy intraligand ~1(#pi#-#pi#*) fluorescence in degassed MeOH at 298 K, and intraligand ~3(#pi#-#pi#*) phosphorescence in a glassy solution (MeOH-EtOH 1:2 at 77K). An emission band observed for 1c (418 nm) and 1d (481 nm) in their solid state emission spectra is ascribed to excimeric emission due to aromatic #pi#-#pi# interactions.