Hydrogen-Bonded Framework of a Cobalt(II) Complex Showing Superior Stability and Field-Induced Slow Magnetic Relaxation

Abstract

A unique hydrogen-bonded organic–inorganic framework (HOIF) constructed from a mononuclear cobalt­(II) complex, [Co­(MCA)2·(H2O)2] (HMCA = 4-imidazole­carboxylic acid), via multiple hydrogen-bonding interactions was synthesized and structurally characterized. The Co­(II) center in the HOIF features a highly distorted octahedral coordination environment. Remarkably, the CoII HOIF showed permanent porosity with superior stability as established by combined thermogravimetric analysis (TGA), variable-temperature infrared spectra (IR), variable-temperature powder X-ray diffraction data (PXRD), and a CO2 isotherm. Structural studies reveal that short multiple hydrogen bonds should be responsible for the superior thermal and chemical stability of a HIOF. Magnetic investigations reveal the large easy-plane magnetic anisotropy of the Co2+ ions with the fitted D values being 22.1 (magnetic susceptibility and magnetization data) and 29.1 cm–1 (reduced magnetization data). In addition, the HOIF exhibits field-induced slow magnetic relaxation at low temperature with an effective energy barrier of U eff = 45.2 cm–1, indicative of a hydrogen-bonded framework single-ion magnet of the compound. The origin of the significant magnetic anisotropy of the complex was also understood from computational studies. In addition, BS-DFT calculations indicate that the superexchange interactions between the neighboring CoII ions are non-negligible anti­ferro­magnetism with J Co–Co = −0.5 cm–1. The foregoing results provide not only a carboxylate–imidazole ligand approach toward a stable HOIF but also a promising way to build a robust single-ion magnet via hydrogen-bond interactions.

Field-induced slow magnetic relaxation behaviours in binuclear cobalt(ii) metallocycles and exchange-coupled clusters

“…In our previous studies, we were interested in pentagonal bipyramidal Fe II and Co II complexes and have achieved their structural extension by linking these highly anisotropic building blocks using various organic linkers and cyanometalates. [26][27][28][29][30][31][32][33][34] These coordination-driven assemblies based on predesigned magnetic building blocks have led to a series of one-dimensional (1D) and 2D magnetic materials, in which the structures and magnetic properties of these coordination polymers can be finely tuned using different bridges. For example, 2D longrange magnetic ordering materials and 2D framework SIMs can be selectively synthesized through paramagnetic and diamagnetic hexacyanometallates.…”

“…30 Very recently, we turned our attention to an octahedral molecular complex as the building unit for the construction of magnetic coordination polymers and supramolecular framework materials. [32][33][34] Interestingly, we achieved structural and magnetic tuning through selective linkers, 32 and obtained two novel hydrogen-bonded SIM frameworks. 33,34 Following these lines, we further turned our attention to a tetrahedral mononuclear complex (HNEt 3 ) 2 [Co ( pdms) 2 ] (H 2 pdms = 1,2-bis(methanesulfonamide)benzene, Scheme 1), which possesses the highest reported effective energy barrier (213 cm −1 ) among the air-stable transitionmetal SIMs.…”

“…[32][33][34] Interestingly, we achieved structural and magnetic tuning through selective linkers, 32 and obtained two novel hydrogen-bonded SIM frameworks. 33,34 Following these lines, we further turned our attention to a tetrahedral mononuclear complex (HNEt 3 ) 2 [Co ( pdms) 2 ] (H 2 pdms = 1,2-bis(methanesulfonamide)benzene, Scheme 1), which possesses the highest reported effective energy barrier (213 cm −1 ) among the air-stable transitionmetal SIMs. 20 Then, this complex has been used as a great magnetic building unit for the development of novel magnetic conductors [35][36][37] and as a molecular model for theoretical investigation, 38,39 and inspired the construction of a radicalbridged dimeric Co II SMM 40 and similar Co II SIMs.…”

Tuning chain topologies and magnetic anisotropy in one-dimensional cobalt(ii) coordination polymers via distinct dicarboxylates

“…It is worth noting that the shortest Co–O bond distances of 1 and 2 are 2.012 and 2.003 Å (Tables S1 and S2, ESI†), respectively, which are very short among the previously reported values for high-spin Co 2+ complexes with Co–O bonds. 20,21 The O axial –Co–O axial angle of 174.36° in 1 is close to linearity, while the angle in 2 is highly deviated (Table 2). These crystal parameters indicate a significant distortion of the octahedral coordination environment of Co 2+ ions in 1 and 2 .…”

“…In fact, the observation of slow relaxation of magnetization under an external dc field ( vide infra ) indirectly supports the negligible magnetic interaction between the Co 2+ ions because the weak magnetic interaction can effectively suppress slow magnetic relaxation behaviour. 17 a ,21 a ,24 Finally, the isolated chains further pack together efficiently through supramolecular interactions, resulting in supramolecular 3D supramolecular networks (Fig. S3 and S4†).…”