Search

Recent interest in potassium-doped p-terphenyl has been fueled by reports of superconductivity at Tc values surprisingly high for organic compounds. Despite these interesting properties, studies of the structure–function relationships within these materials have been scarce. Here, we isolate a phase-pure crystal of potassium-doped p-terphenyl: [K(222)]2[p-terphenyl3]. Emerging antiferromagnetism in the anisotropic structure is studied in depth by magnetometry and electron spin resonance. Combining these experimental results with density functional theory calculations, we describe the antiferromagnetic coupling in this system that occurs in all 3 crystallographic directions. The strongest coupling was found along the ends of the terphenyls, where the additional electron on neighboring p-terphenyls antiferromagnetically couple. This delocalized bonding interaction is reminiscent of the doubly degenerate resonance structure depiction of polyacetylene. These findings hint toward magnetic fluctuation-induced superconductivity in potassium-doped p-terphenyl, which has a close analogy with high Tc cuprate superconductors. The new approach described here is very versatile as shown by the preparation of two additional salts through systematic changing of the building blocks., C.N. thanks Sheldon and Dorothea Buckler for their generous support. Support for this research was provided by the Center for Precision Assembly of Superstratic and Superatomic Solids, an NSF MRSEC (award numbers DMR-1420634 and DMR-2011738), and the Air Force Office of Scientific Research (award number FA9550-18-1-0020). R.H.S. acknowledges support from the Columbia Nano Initiative Postdoctoral Fellowship. X.R. acknowledges support from the NSF CAREER award (NSF DMR-1751949). A.K.B. is supported by the Arnold O. Beckman Fellowship in Chemical Sciences. I.S. is supported by the National Science Foundation under award number CHE-1807654. Single-crystal X-ray diffraction was performed at the Shared Materials Characterization Laboratory at Columbia University, maintained using funding from Columbia University for which we are grateful. Work in Lausanne was supported by the Swiss National Science Foundation. Work in Spain was supported by MICIU (Spain) through Grants PGC2018-096955-B-C44 and PGC2018-093863-B-C22 and Generalitat de Catalunya (2017SGR1506 and 2017SGR1289). E.C. acknowledges support from the Spanish MINECO through the Severo Ochoa Centers of Excellence Program (SEV-2015-0496) and P.A. from the Maria de Maeztu Units of Excellence Program (MDM-2017-0767). S.C. was supported by FONDECYT (Chile) through project 11107163.

A family of new MnII compounds, consisting of seven dinuclear, three mononuclear, and four trinuclear ones, were synthesised using benzoic acid derivatives n-RC6H4COOH, where n-R = 2-MeO, 3-MeO, 4-MeO, or 4-tBu, and 2,2′-bipyridine (bpy) or 1,10-phenantroline (phen) as blocking ligands. The crystal structures of nine of these compounds and the magnetic studies of all of them are reported here. Each type of compound was formed depending on the presence or absence of ClO4− ions, the solvent used, and/or the presence of a small amount of water in the reaction medium. The use of the tert-buthylbenzoate ligand gave unexpected results, very likely due to the steric hindrance caused by the voluminous tBu groups. The EPR spectra of each type of compound give some peculiar features that allow its identification. Attempts to fit these spectra have been made in order to determine the ZFS parameters, D and E, of the MnII ion (for mononuclear and dinuclear systems) or of the ground state (for trinuclear systems). For trinuclear systems, the single-ion ZFS parameters estimated from those of the ground state provided a good simulation of the EPR spectra of these compounds. The EPR signals observed in each case have been rationalised according to the energy level distribution and the plausible population in the excited states. In some particular situations, the sign of DMn could be determined from the fit of the EPR spectra of the antiferromagnetic dinuclear compounds, the source of the difference between the spectra lying in the second excited state.