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)(H 2 O) 4 ](B) 2 }(H 2 O) 6 (where M]Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ , B is barbiturate anion and bipy is 4,4 0 -bipyridine) were obtained and investigated by means of single crystal X-ray diffraction and vibrational (Raman and infrared) spectroscopic techniques. The CoB 2 bipy$10H 2 O, NiB 2 bipy$10H 2 O and CuB 2 bipy$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)(H 2 O) 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 Ni 2+ and Cu 2+ 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)(H 2 O) 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 À1 has been observed, assigned to the CO stretch of the barbiturate anion. In the Raman spectra the most important bands referring to 4,4 0 -bipyridine are the ones at 1616, 1290 and 1020 cm À1 , assigned to d CC/ CN , d ring and d CH modes, respectively. The vibrational results strongly suggest the Zn 2+ compound presents the same molecular arrangement, based on the fact that the spectra of all complexes are similar.

Synthesis, structural studies and vibrational spectroscopy of Fe2+ and Zn2+ complexes containing 4,4′-bipyridine and barbiturate anion

“…The ligand p-electrons involved in the bond imply in a strengthening of the CN bond, and consequently in an increase in the bond order, and with a decrease in the bond length. This result is in a good agreement with the coordination of the pyridine nitrogen atoms of 4,4 0 -bipyridine to the metal ion, and is also supported by the comparison with other analogous compounds reported in the literature [9,34]. Other band which can be observed in the spectra is the one at 1295 cm À1 , assigned to the m ring + dCH combination mode of the bpy ligand.…”

“…Garcia et al [9] synthesized the same complexes with Cu 2+ and Ni 2+ metallic ion, and observed the formation of the cavities via hydrogen interaction formed by the two barbiturates anions and four water molecules crystallization encapsulated the covalent [M(bpy)(H 2 O) 4 ] 2+ linear chains. However these cavities were not observed for the FeB 2 bpyÁ10H 2 O (1) and ZnB 2 bpyÁ10H 2 O (2) complexes investigated here, due to the different localization of the crystallization water molecules responsible by the change of the space group in relation to the Cu 2+ and Ni 2+ complexes (P6 5 22).…”

“…3), which can be classified as moderate to weak due to the interaction distance [9]. These moderate to weak hydrogen bonds have OÁ Á ÁN distances of 2.828(4) Å (N2Á Á ÁO3) for compound 1 and 2.817(4) Å (N2Á Á ÁO3) for compound 2, occurred through of two NH group of one barbiturate ion serves as an hydrogen donor and interact with three carbonyl group hydrogen acceptor of other barbiturate anion of classified mode head-to-tail, these supramolecular interaction occurs with every barbiturates anion in the structure, contributed with stability crystalline arrangement.…”

“…Barbituric acid and their derivatives are compounds containing pyrimidine ring which play an important role in many biological systems, being widely pharmacologically used as sedative hypnotic [14][15][16]. They have also been used as non-linear optical materials (NLO), disperse dyes with strong fluorescent properties, as well as charge generation agents for electrophotography and photoreception [9]. However, investigation focused mainly on crystalline structures of barbiturates with transition metal ions has been incipient [11,17].…”

“…These weaker non-covalent interactions, especially hydrogen bonds, play a crucial role in fundamental biological processes, such as the expression and transfer of genetic information, and are essential for molecular recognition between receptors and substrates as well as construction of complicated arrays through self-organization of molecules in the field of supramolecular chemistry [9].…”