Open-chain hemiketal is stabilized by coordination to a copper (II)

Non-Covalent Interactions in Coordination and Organometallic Chemistry

The problem of non-covalent interactions in coordination and organometallic compounds is a hot topic in modern chemistry, material science, crystal engineering and related fields of knowledge. Researchers in various fields of chemistry and other disciplines (physics, crystallography, computer science, etc.) are welcome to submit their works on this topic for our Special Issue “Non-Covalent Interactions in Coordination and Organometallic Chemistry”. The aim of this Special Issue is to highlight and overview modern trends and draw the attention of the scientific community to various types of non-covalent interactions in coordination and organometallic compounds. In this editorial, I would like to briefly highlight the main successes of our research group in the field of the fundamental study of non-covalent interactions in coordination and organometallic compounds over the past 5 years.

Dysprosium-based complexes with a flat pentadentate donor: a magnetic and ab initio study

The reactivity of the well-known pentadentate N3O2 Schiff base H2L (2,6-bis(2-hydroxyphenyliminomethyl)pyridine) towards a lanthanoid metal, in this case DyIII, has been investigated for the first time. This reactivity markedly depends on the pH of the medium and, accordingly, two different complexes, [Dy(HL)(NO3)2]·H2O (1·H2O) and [Dy(L)(NO3)(EtOH)(H2O)]·2H2O (2·2H2O), could be isolated from dysprosium(iii) nitrate and H2L. In addition, reaction of H2L with dysprosium(iii) chloride in methanol yields [Dy(HL')2][Dy(L)(Cl2)] (3), where H2L' ((6-(2-hydroxyphenyliminomethyl)-2-methoxyhydroxymethyl)pyridine) is an N2O2 hemiacetal donor derived from the partial hydrolysis of the H2L ligand, and subsequent addition of the methanol solvent to the carbonyl group. This latter reaction has been firstly observed for a lanthanoid metal. Single crystal X-ray diffraction studies of 1·1.15Py·0.3CH3C6H5, 2·2H2O and 3 show that the Schiff base is acting as a nearly flat pentadentate donor in all the cases, this behaviour being independent of the deprotonation degree of the phenolic oxygen atoms, both mono- or bisdeprotonated. Complexes 1·1.15Py·0.3CH3C6H5 and 2·2H2O show DyN3O6 cores, with distorted geometries closer to spherical tricapped trigonal prism or spherical capped square antiprism for 1·1.15Py·0.3CH3C6H5 and 2·2H2O, respectively. In the case of 3, the [Dy(HL')2]+ cation shows a dysprosium ion in an N4O4 triangular dodecahedron environment, while the [Dy(L)(Cl2)]- anion displays a DyN3O2Cl2 core with distorted pentagonal bipyramidal geometry. Moreover, attempts to dilute 1·H2O with yttrium yielded single crystals of (Et3NH)[Dy0.09Y0.91(L)(NO3)2] (4), where the Schiff base shows a similar pentadentate coordination mode. Dynamic magnetic studies of 1·H2O, 2·2H2O and 3 show that 2·2H2O and 3 present field-induced slow relaxation of the magnetisation, with Ueff barriers of 46.1(9) and 31.0(7) K for 2·2H2O and 3, respectively, while 1·H2O does not exhibit frequency-dependent peaks of the out of phase susceptibility, even in the presence of an external dc magnetic field. By contrast, the dilute sample 4 behaves as a SIM at zero dc field, with an energy barrier of ca. 49 K. Ab initio calculations using CASSCF methods including spin-orbit effects qualitatively support the obtained magnetic results, indicating that axiality is not the only factor that should be taken into account in order to increase effective energy barriers.