Abstract
The discovery of emergent materials lies at the intersection of chemistry and condensed matter physics. Synthetic chemistry offers a pathway to create materials with the desired physical and electronic structures that support fundamentally new properties. Metal-organic frameworks are a promising platform for bottom-up chemical design of new materials, owing to their inherent chemical predictability and tunability relative to traditional solid-state materials. Herein, we describe the synthesis and magnetic characterization of a new 2,5-dihydroxy-1,4-benzoquinone based material, (NMe2H2)3.5Ga2(C6O4Cl2)3 (1), which features radical-based electronic spins on the sites of a kagomé lattice, a geometric lattice known to engender exotic electronic properties. Vibrational and electronic spectroscopies, in combination with magnetic susceptibility measurements, revealed 1 exhibits mixed valency between the radical-bearing trianionic and diamagnetic tetraanionic oxidation states of the ligand. This unpaired electron density on the ligand forms a partially occupied kagomé lattice where approximately 85% of the lattice sites are occupied with an S = ½ spin. We found that gallium mediates ferromagnetic coupling between ligand spins, creating a ferromagnetic kagomé lattice. By modulation of the interlayer spacing via post-synthetic cation metathesis of 1 to (NMe4)3.5Ga2(C6O4Cl2)3 (2) and (NEt4)2(NMe4)1.5Ga2(C6O4Cl2)3 (3), we determined the nature of the magnetic coupling between neighboring planes is antiferromagnetic. Additionally, we determined the role of the metal in mediating this magnetic coupling by comparison of 2 with the In3+ analogue, (NMe4)3.5In2(C6O4Cl2)3 (4), and we found that Ga3+ supports stronger superexchange coupling between ligand-based spins than In3+. The combination of intraplanar ferromagnetic coupling and interplanar antiferromagnetic coupling exchange interactions suggests these are promising materials to host topological phenomena.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 5922-5928 |
| Number of pages | 7 |
| Journal | Chemical Science |
| Volume | 11 |
| Issue number | 23 |
| DOIs | |
| State | Published - Jun 21 2020 |
Funding
We thank Dr S. C. Coste, Mr B. D. Coleman, and Dr L. Liu for productive discussions and experimental assistance. We thank the ARO for funding this study through W911NF1810006. K. A. C. acknowledges support from the NSF GRFP through DGE-11842165. R. J. S. and J. M. R were supported by the Materials Research Science and Engineering Center at Northwestern University supported by the NSF (DMR1720139). D. P. acknowledges the Army Research Office under Grant No. W911NF-15-1-0017 for nancial support. This work made use of the IMSERC at Northwestern University, which has received support from the So and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the State of Illinois and International Institute for Nanotechnology (IIN). We also used the DOD-HPCMP and the Extreme Science and Engineering Discovery Environment (XSEDE) Stampede 2 at the Texas Advance Computing Center through allocation TG-DMR110085.
ASJC Scopus subject areas
- General Chemistry