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

Abstract

In this work, four new transition metal complexes of general formula {[M(bipy)(H₂O)₄](B)₂}(H₂O)₆ (where MCo²⁺, 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 CoB₂bipy·10H₂O, NiB₂bipy·10H₂O and CuB₂bipy·10H₂O 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 Cu²⁺ 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 δ_CC/CN, δ_ring and δ_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.