Two [Ln4] molecular rings folded as compact tetrahedra.

The design of photoactive ligands may provide access to multifunctional molecular nanomagnets. We report here the design and synthesis of a new multitopic chelating ligand, 1,2-bis-(5-(N'-(pyridine-2-yl-methylene)-carbohydrazide)-3-methyl-thien-3-yl)-cyclopentene (H2L), bearing a photoswitchable spacer and demonstrate that it undergoes reversible photoisomerization in solution. In the presence of the base NaH, H2L reacts with LnCl3 salts (Ln = Dy, Tb) to form the supramolecular assemblies H2O@[Ln4L4Cl4(H2O)4] (Ln = Dy, 1; Tb, 2). The single crystal X-ray diffraction data of 1 and 2 reveal that both compounds consist of highly symmetric molecular rings efficiently folded through intramolecular weak interactions in the form of tetrahedra. This arrangement imparts a conformation to the photochromic spacer of the ligand which inhibits its photoswitching activity. Despite the low symmetry of the coordination geometry around the Ln ions, the Dy analog exhibits slow relaxation of the magnetization. The relaxation rate under various conditions has been investigated, allowing us to elucidate the mechanisms involved in this relaxation.

A Magneto-optical Molecular Device: Interplay of Spin Crossover, Luminescence, Photomagnetism, and Photochromism.

A bis(pyrazolylpyridyl) ligand, L, containing a central photochromic dithienylethene spacer predictably forms a ferrous [Fe2 L3 ]4+ helicate exhibiting spin crossover (SCO). In solution, the compound [Fe2 L3 ](ClO4 )4 (1) preserves the magnetic properties and is fluorescent. The structure of 1 is photo-switchable following the reversible ring closure/opening of the central dithienylethene via irradiation with UV/visible light. This photoisomerization switches on and off some emission bands of 1 and provides a means of externally manipulating the magnetic properties of the assembly.

The effect of potential supramolecular-bond promoters on the DNA-interacting abilities of copper-terpyridine compounds.

Three copper(ii) coordination compounds have been prepared from three different 2,2':6',2''-terpyridine-based ligands, which have been selected to investigate the potential role of supramolecular interactions on the DNA-interacting and cytotoxicity properties of the corresponding metal complexes. Hence, the ligands 4'-((naphthalen-2-yl)methoxy)-2,2':6',2''-terpyridine () and 4'-((1H-benzo[d]imidazol-2-yl)methoxy)-2,2':6',2''-terpyridine () have been synthesized from commercially-available 4'-chloro-2,2':6',2''-terpyridine (), and their copper(ii) complexes have been obtained by reaction with copper(ii) nitrate. The DNA-interacting abilities of the corresponding compounds [Cu()(H2O)(NO3)2] (), [Cu()(NO3)(H2O)](NO3)(MeOH) () and [Cu()(NO3)(H2O)](NO3) () have been investigated using different techniques, and cytotoxicity assays with several cancer cell lines have revealed interesting features, viz. the more efficient complex is , which although it does not act as a DNA cleaver, displays the most effective DNA-interacting and cytotoxic properties, compared to and .

A new type of paddle-wheel coordination complex.

In the presence of Na(+) ions, the reaction of the ligand 2-hydroxy-1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-benzene, H5L4, with M(AcO)2 salts (M = Mn, Co) gathers the conditions for the assembly of coordination complexes (NBu4)3[M2Na2(H2L4)3] (M = Mn(II) 1 and Co(II) 2), which exhibit a new paddle-wheel structure. The features of this new category of compounds are discussed as well as their magnetic properties and solution behaviour.