Rotaxane CoII Complexes as Field-Induced Single-Ion Magnets

Abstract

Mechanically chelating ligands have untapped potential for the engineering of metal ion properties by providing reliable control of the number, nature and geometry of donor atoms, akin to how a protein cavity controls the properties of bound metal ions. Here we demonstrate this principle in the context of Co<sup>II</sup>-based single-ion magnets. Using multi-frequency EPR, susceptibility and magnetization measurements we found that these complexes show some of the highest zero field splittings reported for five-coordinate Co<sup>II</sup> complexes to date. The predictable coordination behavior of the interlocked ligands allowed the magnetic properties of their Co<sup>II</sup> complexes to be evaluated computationally <i>a priori </i>and our combined experimental and theoretical approach enabled us to rationalize the observed trends. The predictable magnetic behavior of the rotaxane Co<sup>II</sup> complexes demonstrates that interlocked ligands offer a new strategy to design metal complexes with interesting functionality.

Cooperative Capture Synthesis of Functionalized Heterorotaxanes─Chemical Scope, Kinetics, and Mechanistic Studies

“…A series of monofunctionalized β-CD-R derivatives featuring reactive groups that can be used in further conjugation steps were synthesized (compounds 3−11, Scheme 1). The β-CD-R macrocycles included species with azides (4 and 6), primary amines (7 and 8), carboxylic acid ( 5 11), CB [6], and the anthracene-azido compound 2 in a 1:1:2:2 stoichiometric ratio is presented in Scheme 2. In the complete (full) reaction pathway, an initial molecular inclusion complex (1 ⊃ β-CD-R) forms between the biphenyl-dialkyne guest molecule 1 and β-CD-R derivative.…”

“…1 Developing this level of complexity often involves combining matter in ways that use noncovalent interactions to synthesize compounds whose physical and biochemical properties extend beyond the sum of the individual components. 2,3 Supramolecular chemists strive to achieve the same complexity as nature, and over the last three decades, scientists have used the principles of self-assembly to produce artificial molecular machines, 4−7 molecular switches, 8 novel catalysts, 9,10 single molecule magnets, 11 and new materials for applications in biomedicine. 12−21 Supramolecular compounds derived from molecular cages, 22−33 and from molecularly interlocked molecules like rotaxanes 34 and catenanes, 35−38 have shown promise in several applications 14,15 such as delivery vehicles 39−42 for controlling the release of cytotoxic drugs, 43−45 as biosensors for DNA recognition, 46,47 and as reporter probes for diagnostic molecular imaging.…”