Structural diversity in the coordination compounds of cobalt, nickel and copper with N-alkylglycinates: crystallographic and ESR study in the solid state

Abstract

Reactions of N-methylglycine (HMeGly), N-ethylglycine-hydrochloride (H₂EtGlyCl) and N-propylglycine-hydrochloride (H₂PrGlyCl) with cobalt(II), nickel(II) and copper(II) ions in aqueous solutions resulted in ten new coordination compounds [Co(MeGly)₂(H₂O)₂] (1), [{Co(MeGly)₂}₂(μ-OH)₂]·2H₂O (1d), [Cu(MeGly)₂(H₂O)₂] (2α), [Co(EtGly)₂(H₂O)₂] (3), [Ni(EtGly)₂(H₂O)₂] (4), [Cu(μ-EtGly)₂]_n (5p), [Co(PrGly)₂(H₂O)₂] (6), [Ni(PrGly)₂(H₂O)₂] (7), and two polymorphs of [Cu(PrGly)₂(H₂O)₂] (8α and 8β). Compounds were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, thermal analysis and X-band electron spin resonance (ESR) spectroscopy. These studies revealed a wide range of structural types including monomeric, dimeric and polymeric architectures, as well as different polymorphs. In all monomeric compounds, except 2α, and in the coordination polymer 5p hydrogen bonds interconnect the molecules into 2D layers with the alkyl chain pointing outward of the layer. In 2α and in the dimeric compound 1d hydrogen bonds link the molecules into 3D structures. 1d with cobalt(III), and 4 and 7 with nickel(II) are ESR silent. The ESR spectra of 1, 3 and 6 are characteristic for paramagnetic high-spin cobalt(II). The ESR spectra of all copper(II) coordination compounds show that the unpaired copper electron is located in the d_x²−y² orbital, being in agreement with the elongated octahedral geometry.