The Schiff base N,NЈ-bis(salicylidene)-1,5-diamino-3-oxapentane (H 2 L) and its lanthanide(III) complexes, PrL(NO 3 )(DMF)(H 2 O) (1) and Ho 2 L 2 (NO 3 ) 2 ·2H 2 O (2), were synthesized and characterized by physicochemical and spectroscopic methods. Single crystal X-ray structure analysis revealed that complex 1 is a discrete mononuclear species. The Pr III ion is nine-coordinate, forming a distorted capped square antiprismatic arrangement. Complex 2 is a centrosymmetric dinuclear neutral entity in which the Ho III ion is eight-coordinate with distorted square antiprismatic arrangement. The DNA-binding proper-

A V-shaped ligand bis(2-benzimidazol-2-ylmethyl)benzylamine L(1) with its two derivatives bis(N-methylbenzimidazol-2-ylmethyl)benzylamine L(2) and bis(N-benzylbenzimidazol-2-ylmethyl)benzylamine L(3) have been prepared. Reaction of these shape-specific designed ligands with Ag(pic) (pic = picrate) afforded three novel complexes, namely, [Ag(2)L(1)(2)](pic)(2)1, [Ag(2)L(2)(2)](pic)(2)·2DMF 2 and [AgL(3)(pic)] 3. The ligands and complexes were characterized on the basis of elemental analysis, UV-Vis, IR, NMR spectroscopy and X-ray crystallography. Complex 1 is a dinuclear metallacycle with a 2-fold rotational symmetry in which two syn-conformational L(1) ligands are connected by two linearly coordinated Ag(I) atoms. Due to the strong interaction between two adjacent Ag(I) atoms, the coordination mode of the central Ag(I) atom can be described as T-shaped. Complex 2 consists of a centrosymmetric dinuclear pore canal structure assembled from two nearly linearly coordinated Ag(I) atoms and two L(2) ligands. The structure of complex 3 adopts a four-coordinate environment for AgN(2)O(2), with the counterion participating in an eight-shaped geometry. In order to explore the relationship between the structure and biological properties, the DNA-binding properties have been investigated by viscosity measurements, electronic absorption, and fluorescence. The results suggest that the ligands and complexes bind to DNA in an intercalation mode, and their binding affinities for DNA are also different. Moreover, the three Ag(I) complexes also exhibited potential antioxidant properties in vitro studies.

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A pentadentate Schiff base bis(N-salicylidene)-3-oxapentane-1,5-diamine (H 2 L) and its lanthanide (III) complexes, [GdL(NO 3 )(DMF)(H 2 O)] (1) and [Dy 2 L 2 (NO 3 ) 2 ]·2H 2 O (2), have been synthesized and characterized by physical, chemical, and spectroscopic methods. Single crystal X-ray structure reveals that 1 is a discrete mononuclear species with nine-coordinate Gd(III) in a distorted monocapped square antiprism geometry. Complex 2 is a centrosymmetric binuclear neutral entity, in which Dy(III) is eight-coordinate in a distorted square antiprism. Electronic absorption titration spectra, ethidium bromide competitive experiments, and viscosity measurements indicate that both the ligand and complexes bind calf thymus DNA, presumably via groove binding. Investigations of antioxidant activities show that both complexes have some scavenging effects for hydroxyl and superoxide radicals.