Here we present the synthesis and characterization of a hybrid vanadium-organic coordination polymer with robust magnetic order, a Curie temperature TC of ∼110 K, a coercive field of ∼5 Oe at 5 K, and a maximum mass magnetization of about half that of the benchmark ferrimagnetic vanadium(tetracyanoethylene)~2 (V·(TCNE)~2). This material was prepared using a new tetracyano-substituted quinoidal organic small molecule 7 based on a tricyclic heterocycle 4-hexyl-4H-pyrrolo[2,3-d:5,4-d′]bis(thiazole) (C6-PBTz). Single crystal X-ray diffraction of the 2,6-diiodo derivative of the parent C6-PBTz, showed a disordered hexyl chain and a nearly linear arrangement of the substituents in positions 2 and 6 of the tricyclic core. Density functional theory (DFT) calculations indicate that C6-PBTz-based ligand 7 is a strong acceptor with an electron affinity larger than that of TCNE and several other ligands previously used in molecular magnets. This effect is due in part to the electron-deficient thiazole rings and extended delocalization of the frontier molecular orbitals. The ligand detailed in this study, a representative example of fused heterocycle aromatic cores with extended π conjugation, introduces new opportunities for structure–magnetic-property correlation studies where the chemistry of the tricyclic heterocycles can modulate the electronic properties and the substituent at the central N-position can vary the spatial characteristics of the magnetic polymer.
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This work was supported by the Center for Emergent Materials, an NSF MRSEC under award number DMR-1420451, NSF DMR-1523611, and Infrastructure Seed Award (NSF Grant #IIA-1301346). We acknowledge the NSF MRI Program (CHE-1726652) and the UNT for supporting the acquisition of the Rigaku XtaLAB Synergy-S X-ray diffractometer. The computational work at the University of Kentucky (UK) was supported in part by start-up funds received from the UK Vice President for Research and the UK Center for Applied Energy Research (CAER).
Electronic supplementary information (ESI) available. CCDC 1819816, 1819817 and 1868490 for compounds 5, 6 and 7, respectively. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8ra05697h
Getmanenko, Yulia A.; Mullins, Christopher S.; Nesterov, Vladimir N.; Lake, Stephanie; Risko, Chad; and Johnston-Halperin, Ezekiel, "Magnetic Ordering in a Vanadium-Organic Coordination Polymer Using a Pyrrolo[2,3-d:5,4-d']bis(thiazole)-Based Ligand" (2018). Chemistry Faculty Publications. 138.