The recent discovery of two-dimensional (2D) magnets [1][2][3] offers unique opportunities for the experimental exploration of low-dimensional magnetism 4 and the magnetic proximity effects 5,6 , and for the development of novel magnetoelectric, magnetooptic and spintronic devices 7,8 . These advancements call for 2D materials with diverse magnetic structures as well as effective probes for their magnetic symmetries, which is key to understanding intralayer magnetic order and interlayer magnetic coupling [9][10][11] . However, traditional techniques do not probe magnetic symmetry; these examples include magneto-optical Kerr effect 2,3 , reflective magnetic circular dichroism and Raman spectroscopy [12][13][14] , anomalous Hall effect 15 , tunneling magnetoresistance 16,17 , spin-polarized scanning tunneling microscopy 9 , and single-spin scanning magnetometry 18 . Here we apply second harmonic generation (SHG), a technique acutely sensitive to symmetry breaking, to probe the magnetic structure of a new 2D magnetic semiconductor, CrSBr. We find that CrSBr monolayers are ferromagnetically ordered below 146 K, an observation enabled by the discovery of a giant magnetic dipole SHG effect in the centrosymmetric 2D structure. In multilayers, the ferromagnetic monolayers are coupled antiferromagnetically, with the Néel temperature notably increasing with decreasing layer number. The magnetic structure of CrSBr, comprising spins co-aligned in-plane with rectangular unit cell, differs markedly from the prototypical 2D hexagonal magnets CrI3 and Cr2Ge2Te6 with out-of-plane moments.
1,3,5-Tris(4-carboxyphenyl)benzene assembles into an intricate 8-fold polycatenated assembly of (6,3) hexagonal nets formed through hydrogen bonds and π-stacking. One polymorph features 56 independent molecules in the asymmetric unit, the largest Z' reported to date. The framework is permanently porous, with a BET surface area of 1095 m(2) g(-1) and readily adsorbs N2, H2 and CO2.
Selective access to a targeted isomer
is often critical in the
synthesis of biologically active molecules. Whereas small-molecule
reagents and catalysts often act with anticipated site- and stereoselectivity,
this predictability does not extend to enzymes. Further, the lack
of access to catalysts that provide complementary selectivity creates
a challenge in the application of biocatalysis in synthesis. Here,
we report an approach for accessing biocatalysts with complementary
selectivity that is orthogonal to protein engineering. Through the
use of a sequence similarity network (SSN), a number of sequences
were selected, and the corresponding biocatalysts were evaluated for
reactivity and selectivity. With a number of biocatalysts identified
that operate with complementary site- and stereoselectivity, these
catalysts were employed in the stereodivergent, chemoenzymatic synthesis
of azaphilone natural products. Specifically, the first syntheses
of trichoflectin, deflectin-1a, and lunatoic acid A were achieved.
In addition, chemoenzymatic syntheses of these azaphilones supplied
enantioenriched material for reassignment of the absolute configuration
of trichoflectin and deflectin-1a based on optical rotation, CD spectra,
and X-ray crystallography.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.