Templated Growth of a Spin-Frustrated Cluster Fragment of MnBr2 in a Metal−Organic Framework

17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.1021/acs.inorgchem.1c01345The metal−organic framework Zr6O4(OH)4(bpydc)6 (bpydc2− = 2,2′-bipyridine-5,5′-dicarboxylate) is used to template the growth of a cluster fragment of the two-dimensional solid MnBr2, which was predicted to exhibit spin frustration. Single-crystal and powder X-ray diffraction analyses reveal a cluster with 19 metal ions arranged in a triangular lattice motif. Static magnetic susceptibility measurements indicate antiferromagnetic coupling between the high-spin (S = 5/2) MnII centers, and dynamic magnetic susceptibility data suggest population of low-lying excited states, consistent with magnetic frustration. Density functional theory calculations are used to determine the energies for a subset of thousands of magnetic configurations available to the cluster. The Yamaguchi generalized spin-projection method is then employed to construct a model for magnetic coupling interactions within the cluster, enabling facile determination of the energy for all possible magnetic configurations. The confined cluster is predicted to possess a doubly degenerate, highly geometrically frustrated ground state with a total spin of STotal = 5/2.This research was supported through a Multidisciplinary University Research Initiatives Program funded by the U.S. Department of Defense, Office of Naval Research, under Award N00014-15-1-2681. Single-crystal X-ray diffraction experiments were performed at Beamline 11.3.1 at the Advanced Light Source, Lawrence Berkeley National Laboratory. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract DE-AC02-05CH11231