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Encapsulation of liquid guest molecules in hydrogen-bonded frameworks permits analysis of their preferred conformations through single crystal X-ray diffraction. 

Crystalline fibers of the hydrogen-bonded framework bis(guanidinium) naphthalene-1,5-disulfonate, (G)2(1,5-NDS), with ethanol guest molecules twist as they grow when deposited from solution under conditions that favor low nucleation densities and high branching rates. Spherulites comprising helicoidal fibers with a pitch of 3.4 ± 0.5 μm display rhythmic concentric variations in interference colors between crossed polarizers. Tightly packed fibers and platelets, systematically change orientations between flat-on and edge-on crystallites with respect to the substrate surface. Mueller matrix imaging reveals periodic oscillations in the absolute magnitude of the linear retardance and an associated bisignate circular retardance. Single-crystal X-ray diffraction data demonstrates that the twisted (G)2(1,5-NDS)⊃EtOH crystals adopt a bilayer packing motif with ethanol as guest molecules (space group P1 ̅). When the banded spherulite films were subsequently heated at 130°C, the solvated phase was converted to a guest-free crystalline phase (space group P21/c). This transition resulted in loss of linear retardance. 

Abstract International relations scholarship concerns dyads, yet standard modeling approaches fail to adequately capture the data generating process behind dyadic events and processes. As a result, they suffer from biased coefficients and poorly calibrated standard errors. We show how a regression-based approach, the Additive and Multiplicative Effects (AME) model, can be used to account for the inherent dependencies in dyadic data and glean substantive insights in the interrelations between actors. First, we conduct a simulation to highlight how the model captures dependencies and show that accounting for these processes improves our ability to conduct inference on dyadic data. Second, we compare the AME model to approaches used in three prominent studies from recent international relations scholarship. For each study, we find that compared to AME, the modeling approach used performs notably worse at capturing the data generating process. Further, conventional methods misstate the effect of key variables and the uncertainty in these effects. Finally, AME outperforms standard approaches in terms of out-of-sample fit. In sum, our work shows the consequences of failing to take the dependencies inherent to dyadic data seriously. Most importantly, by better modeling the data generating process underlying political phenomena, the AME framework improves scholars’ ability to conduct inferential analyses on dyadic data. 

Hydrogen-bonded frameworks (HBFs) have been studied for decades owing to their fascinating and diverse architectures, always with an eye toward the role of hydrogen bonding in their design as well as their utility in various applications. This review addresses recent advances in HBFs that illustrate their versatility and utility stemming from their unique attributes compared with other classes of molecular frameworks. Guanidinium organosulfonate hydrogen-bonded frameworks, pioneered in our lab and one of the most extensive and versatile collections of HBFs, are used to illustrate molecular design concepts and the principle of architectural isomerism that expands access to a greater structural landscape. Recognizing the growing role of computation in materials design, from ab initio methods to machine learning, this review also touches on their emerging use in the design and synthesis of HBFs. The growth of the HBF arsenal promises continuing innovations, with applications ranging from electronic materials and chemical separations to gas adsorption and catalysis. 

The concept of Eshelby untwisting, the effect of an axial screw dislocation driving an intrinsically twisted nanocrystal towards a straighter configuration more consistent with long–range translational symmetry, is introduced here. Force-field simulations of nanorods built from the enantiomorphous (space groups, P 3 1 21 and P 3 2 21) crystal structures of benzil (C 6 H 5 –C(O)–C(O)–C 6 H 5 ) were previously shown to twist in opposite directions, even in the absence of dislocations. Here, both right- and left-handed screw dislocations were introduced into benzil nanorods in silico . For rods built from the P 3 2 21 enantiomorph, dislocations with negative Burgers vectors increased the right-handed twisting already present in the intrinsically twisted structures without dislocations, whereas dislocations with positive Burgers vectors drove the twisted structure back towards a straight configuration, untwisting. In the dynamic simulations, the P 3 2 21 helicoid endowed with a positive Burgers vector ultimately twisted back through the straight configuration, until a helicoid of opposite sense from that of the starting structure, was obtained. The bearing of these observations on the propensity of small crystals to adopt non-polyhedral morphologies is discussed.