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

Arthroscopic partial meniscectomy for a degenerative meniscus tear : a 5 year follow-up of the placebo-surgery controlled FIDELITY (Finnish Degenerative Meniscus Lesion Study) trial

Objectives To assess the long-term effects of arthroscopic partial meniscectomy (APM) on the development of radiographic knee osteoarthritis, and on knee symptoms and function, at 5 years follow-up. Design Multicentre, randomised, participant- and outcome assessor-blinded, placebo-surgery controlled trial. Setting Orthopaedic departments in five public hospitals in Finland. Participants 146 adults, mean age 52 years (range 35-65 years), with knee symptoms consistent with degenerative medial meniscus tear verified by MRI scan and arthroscopically, and no clinical signs of knee osteoarthritis were randomised. Interventions APM or placebo surgery (diagnostic knee arthroscopy). Main outcome measures We used two indices of radiographic knee osteoarthritis (increase in Kellgren and Lawrence grade >= 1, and increase in Osteoarthritis Research Society International (OARSI) atlas radiographic joint space narrowing and osteophyte sum score, respectively), and three validated patient-relevant measures of knee symptoms and function ( Western Ontario Meniscal Evaluation Tool (WOMET), Lysholm, and knee pain after exercise using a numerical rating scale). Results There was a consistent, slightly greater risk for progression of radiographic knee osteoarthritis in the APM group as compared with the placebo surgery group (adjusted absolute risk difference in increase in Kellgren-Lawrence grade >= 1 of 13%, 95% CI -2% to 28%; adjusted absolute mean difference in OARSI sum score 0.7, 95% CI 0.1 to 1.3). There were no relevant between-group differences in the three patient-reported outcomes: adjusted absolute mean differences (APM vs placebo surgery), -1.7 (95% CI -7.7 to 4.3) in WOMET, -2.1 (95% CI -6.8 to 2.6) in Lysholm knee score, and -0.04 (95% CI -0.81 to 0.72) in knee pain after exercise, respectively. The corresponding adjusted absolute risk difference in the presence of mechanical symptoms was 18% (95% CI 5% to 31%); there were more symptoms reported in the APM group. All other secondary outcomes comparisons were similar. Conclusions APM was associated with a slightly increased risk of developing radiographic knee osteoarthritis and no concomitant benefit in patient-relevant outcomes, at 5 years after surgery.Peer reviewe

Author Correction: Limits to the strain engineering of layered square-planar nickelate thin films

Correction to: Nature Communicationshttps://doi.org/10.1038/s41467-023-37117-4, published online 16 March 2023 In the Acknowledgements section of this article the grant number relating to NSF was incorrectly given as DMR 2045826 and should have been DMR-2045826. The original article has been corrected

Size, Shape and Structure Dictate Magnetic Behavior of Metal Halide Clusters and Layered Metal–Organic Frameworks

Nanoscale materials display emergent electronic and magnetic properties that are highly correlated to their size and shape. The work in this dissertation describes efforts to synthesize nanoscale materials including molecular clusters and layered solids with exquisite control over size and shape. Particular emphasis is paid to studying the magnetic properties of these materials and how these properties relate to those of their bulk counterparts. Chapter 1 introduces basic concepts of magnetism including interactions between spin centers. The nature of these interactions dictates many magnetic properties and is essential in understanding the behavior of the materials contained within this dissertation. Furher emphasis is paid to the effects of quantum confinement on magnetic properties, and major advances in this field are provided. Finally, general strategies to purposefully control the size and shape of confined materials are highlighted along with illustrative examples. Chapter 2 describes the synthesis of atomically precise metal(II) halide clusters (M19X38, M = Fe, Co, Ni; X = Cl, Br) using the metal–organic framework Zr6O4(OH)4(bpydc)6 (bpydc2− = 2,2′-bipyridine-5,5′-dicarboxylate) as a template. Single-crystal X-ray diffraction techniques reveal that these clusters represent fragments excised from a single layer of the bulk, layered structure of the corresponding parent metal halide. Magnetometry and Mössbauer spectroscopy are then used the probe the magnetic behavior of these clusters. Remarkably, the intralayer ferromagnetic magnetic exchange pathways characteristic of the bulk materials are conserved in the clusters, leading to the isolation of high-spin magnetic ground states as well as superparamagnetism in the case of Fe19Cl38 clusters. While Chapter 2 focuses on the magnetic behavior of metal(II) halide clusters with predominantly ferromagnetic exchange coupling between spin centers, Chapter 3 focuses on the behavior of clusters with antiferromagnetic exchange coupling. In particular, the magnetic properties of a Mn19Br38 cluster are studied. In this cluster, spin centers are arranged on a triangular lattice. This topology combined with antiferromagnetic exchange correlations can be expected to lead to a geometrically frustrated magnetic ground state. Magnetometry as well as computational methods are used to probe the magnetic behavior of this cluster and confirm a highly frustrated ground state spin configuration. Chapter 4 focuses on the synthesis of a promising new metal–organic framework Cr(pz)2 (pz = pyrazine) that has exceptional magnetic properties. The framework is a layered material constructed of a square net of Cr(II) cations that are bridged by singly reduced pz radical anions. The framework is ferrimagnetic with an ordering temperature of 242 °C and a coercive field of 0.75 T at room temperature, extremely impressive parameters for a metal–organic system. Currently available synthetic methods, however, only yield a microcrystalline powder that is not amenable to in depth characterization techniques. This chapter therefore explores potential synthetic routes toward single-crystals or thin films of Cr(pz)2 using molecular precursors

Tuning Nitric Oxide Adsorption in Cobalt–Triazolate Frameworks

Nitric oxide (NO) is an important signaling molecule in biological systems, and as such the ability of certain porous materials to reversibly adsorb NO is of interest for medical applications. Metal–organic frameworks have been explored for their ability to reversibly bind NO at coordinatively-unsaturated metal sites, however the influence of metal coordination environment on NO adsorption has yet to be studied in detail. Here, we examine NO adsorption in the frameworks Co2Cl2(bbta) and Co2(OH)2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) via gas adsorption, infrared spectroscopy, powder X-ray diffaction, and magnetometry measurements. While NO adsorbs reversibly in Co2Cl2(bbta) without electron-transfer, adsorption of low pressures of NO in Co2(OH)2(bbta) is accompanied by charge transfer from the cobalt(II) centers to form a cobalt(III)–NO− adduct, as supported by diffraction and infrared spectroscopy data. At higher pressures of NO, characterization data support additional uptake of the gas and disproportionation of the bound NO to form a cobalt(III)–nitro (NO2−) species and N2O gas, a transformation that appears to be facilitated in part by stabilizing hydrogen bonding interactions between the bound NO2− and framework hydroxo groups. This reactivity represents a rare example of reductive NO-binding in a metal–organic framework and demonstrates that NO binding can be tuned by changing the coordination environment of the framework metal centers.</p

Influence of the primary and secondary coordination spheres on nitric oxide adsorption and reactivity in cobalt(ii)-triazolate frameworks.

Nitric oxide (NO) is an important signaling molecule in biological systems, and as such, the ability of porous materials to reversibly adsorb NO is of interest for potential medical applications. Although certain metal-organic frameworks are known to bind NO reversibly at coordinatively unsaturated metal sites, the influence of the metal coordination environment on NO adsorption has not been studied in detail. Here, we examine NO adsorption in the frameworks Co2Cl2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) and Co2(OH)2(bbta) using gas adsorption, infrared spectroscopy, powder X-ray diffraction, and magnetometry. At room temperature, NO adsorbs reversibly in Co2Cl2(bbta) without electron transfer, with low temperature data supporting spin-crossover of the NO-bound cobalt(ii) centers of the material. In contrast, adsorption of low pressures of NO in Co2(OH)2(bbta) is accompanied by charge transfer from the cobalt(ii) centers to form a cobalt(iii)-NO- adduct, as supported by diffraction and infrared spectroscopy data. At higher pressures of NO, characterization data indicate additional uptake of the gas and disproportionation of the bound NO to form a cobalt(iii)-nitro (NO2 -) species and N2O gas, a transformation that appears to be facilitated by secondary sphere hydrogen bonding interactions between the bound NO2 - and framework hydroxo groups. These results provide a rare example of reductive NO binding in a cobalt-based metal-organic framework, and they demonstrate that NO uptake can be tuned by changing the primary and secondary coordination environment of the framework metal centers

Correction: Influence of the primary and secondary coordination spheres on nitric oxide adsorption and reactivity in cobalt(ii)-triazolate frameworks.

[This corrects the article DOI: 10.1039/D1SC03994F.]

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

The 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

Influence of Metal Substitution on the Pressure-Induced Phase Change in Flexible Zeolitic Imidazolate Frameworks

Metal–organic frameworks that display step-shaped adsorption profiles arising from discrete pressure-induced phase changes are promising materials for applications in both high-capacity gas storage and energy-efficient gas separations. The thorough investigation of such materials through chemical diversification, gas adsorption measurements, and in situ structural characterization is therefore crucial for broadening their utility. We examine a series of isoreticular, flexible zeolitic imidazolate frameworks (ZIFs) of the type M(bim)2 (SOD; M = Zn (ZIF-7), Co (ZIF-9), Cd (CdIF-13); bim– = benzimidazolate), and elucidate the effects of metal substitution on the pressure-responsive phase changes and the resulting CO2 and CH4 step positions, pre-step uptakes, and step capacities. Using ZIF-7 as a benchmark, we reexamine the poorly understood structural transition responsible for its adsorption steps and, through high-pressure adsorption measurements, verify that it displays a step in its CH4 adsorption isotherms. The ZIF-9 material is shown to undergo an analogous phase change, yielding adsorption steps for CO2 and CH4 with similar profiles and capacities to ZIF-7, but with shifted threshold pressures. Further, the Cd2+ analogue CdIF-13 is reported here for the first time, and shown to display adsorption behavior distinct from both ZIF-7 and ZIF-9, with negligible pre-step adsorption, a ~50% increase in CO2 and CH4 capacity, and dramatically higher threshold adsorption pressures. Remarkably, a single-crystal-to-single-crystal phase change to a pore-gated phase is also achieved with CdIF-13, providing insight into the phase change that yields step-shaped adsorption in these flexible ZIFs. Finally, we show that the endothermic phase change of these frameworks provides intrinsic heat management during gas adsorption. </p