Supramolecular structures and fluorescence properties of three transition-metal complexes

Three mononuclear transition-metal(II) compounds [Co(imidazole)₆]CO₃ · 5H₂O (1), [Co(nicotinate)₂(H₂O)₄] (2) and [Mn(isonicotinate)₂(H₂O)₄] (3) ware obtained under the hydrothermal conditions. It deserves to note that they all exhibit interesting supramolecular topologies: in a crystal host of 1 three crystallographically unique free H₂O molecules form a two-dimensional (2-D) water network based on the cyclic dodecamers with the occluded CO₃^{2 -} anions; both 2 and 3 possess 3-D network structures formed through the π-π stacking interactions of the pyridine rings and multi-types of O⋯Ow hydrogen-bonded interactions. All of these compounds show the strong fluorescence emissions with the peaks at 389, 650 and 390-420 nm (broad band) when excited at 220, 360 and 254 nm, respectively, which can be assigned to the charge transfer between the metal and the ligand.