An intriguing hydrogen bond arrangement of polymeric 1D chains of 4,4 '-bipyridine coordinated to Co2+, Ni2+, Cu2+ and Zn2+ ions having barbiturate as counterions in a 3D network

In this work, four new transition metal complexes of general formula {[M(bipy)(H2O)(4)](B)(2)}(H2O)(6) (where M=Co2+, Ni2+, Cu2+ and Zn2+, B is barbiturate anion and bipy is 4,4'-bipyridine) were obtained and investigated by means of single crystal X-ray diffraction and vibrational (Raman and infrared) spectroscopic techniques. The CoB(2)bipy center dot 10H(2)O, NiB(2)bipy center dot 10H(2)O and CuB(2)bipy center dot 10H(2)O basic units give rise to polymers, where Ni(II) and Cu(II) compounds are isomorphous, however all compounds present the same molecular structure. The metal sites appear in a distorted octahedral geometry coordinated by two pyridine nitrogen atoms and four oxygen atoms from coordinated water molecules. Each structure showing one covalent linear [M(bipy)(H2O)(4)](2+) chains one-dimensional, which interact by hydrogen-bonding with the barbiturate anion and crystallization water resulting in a 3D arrangement. The analysis of the Ni2+ and Cull complexes' structures show flexible 2D hydrogen bonded networks being constructed by the barbiturate anions and the crystallization waters molecules, which may be deemed to be the host, while the robust 1D [M(bipy)(H2O)(4)](2+) chains may be deemed to be the guest, in a very intriguing and interesting structure. The vibrational spectra of the compounds are very similar, in agreement to the crystal data. In all infrared spectra a medium band at 1690 cm(-1) has been observed, assigned to the CO stretch of the barbiturate anion. In the Raman spectra the most important bands referring to 4,4'-bipyridine are the ones at 1616, 1290 and 1020 cm(-1), assigned to delta(CC/CN), delta(ring) and delta(CH) modes, respectively. The vibrational results strongly suggest the Zn2+ compound presents the same molecular arrangement, based on the fact that the spectra of all complexes are similar.