Interaction of Copper(II) with Ditopic Pyridyl-β-diketone Ligands: Dimeric, Framework, and Metallogel Structures

The interaction of Cu(II) with three beta-diketone ligands of type (RC)-C-1(O)CH2C(O)R-2 (where R-1 = 2-, 3-, or 4-pyridyl and R-2 = C6H5, respectively), HL1-HL3, along with the X-ray structures and the pK(a) values of each ligand, are reported. HL1 yields a dimeric complex of type [Cu(L-1)(2)](2). In this structure, two deprotonated HL1 ligands coordinate in a trans planar fashion around each Cu(II) center, one oxygen from each CuL2 unit bridges to an axial site of the second complex unit such that both Cu(II) centers attain equivalent five-coordinate square pyramidal geometries. The two-substituted pyridyl groups in this complex do not coordinate, perhaps reflecting steric factors associated with the closeness of the pyridyl nitrogen to the attached (conjugated) beta-diketonato backbone of each ligand. The remaining two Cu(II) species, derived from HL2 and HL3, are both coordination polymers of type [Cu(L)(2)](n) in which the terminal pyridine group of each ligand is intermolecularly linked to an adjacent copper center to generate the respective infinite structures. HL2 was also demonstrated to form a fibrous metallogel when reacted with CuCl2 in an acetonitrile/water mixture under defined conditions.