The interaction of Cu(II) with three β-diketone ligands of type R 1 C(O)CH 2 C(O)R 2 (where R 1 = 2-, 3-, or 4-pyridyl and R 2 = C 6 H 5 , respectively), HL 1 -HL 3 , along with the X-ray structures and the pK a values of each ligand, are reported. HL 1 yields a dimeric complex of type [Cu(L 1 ) 2 ] 2 . In this structure, two deprotonated HL 1 ligands coordinate in a trans planar fashion around each Cu(II) center, one oxygen from each CuL 2 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) β-diketonato backbone of each ligand. The remaining two Cu(II) species, derived from HL 2 and HL 3 , 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. HL 2 was also demonstrated to form a fibrous metallogel when reacted with CuCl 2 in an acetonitrile/water mixture under defined conditions.

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Abstract. Reaction of equimolar amounts of Cu(OAc) 2 ·H 2 O and bis [4-(3-ethoxysalicylideneamino)2 ) in a 1:1 THF/MeOH mixture leads to the formation of structure-analogous Cu II helicates of the composition [{Cu 2 L 2 }(H 2 O) 2 }]·4H 2 O. The helicates form left-and right-handed hydrogen bonded strands using the bound water mole-