aOne of the main advantages of graphene oxide (GO) over its non-oxidized counterpart is its ability to form stable solutions in water and some organic solvents. At the same time, the nature of GO solutions is not completely understood; the existing data are scarce and controversial. Here, we demonstrate that the solubility of GO, and the stability of the as-formed solutions depend not just on the solute and solvent cohesion parameters, as commonly believed, but mostly on the chemical interactions at the GO/solvent interface. By the DFT and QTAIM calculations, we demonstrate that the solubility of GO is afforded by strong hydrogen bonding established between GO functional groups and solvent molecules.The main functional groups taking part in hydrogen bonding are tertiary alcohols; epoxides play only a minor role. The magnitude of the bond energy values is significantly higher than that for typical hydrogen bonding. The hydrogen bond energy between GO functional groups and solvent molecules decreases in the sequence: water 4 methanol 4 ethanol. We support our theoretical results by several experimental observations including solution calorimetry. The enthalpy of GO dissolution in water, methanol and ethanol is À0.1815 AE 0.0010, À0.1550 AE 0.0012 and À0.1040 AE 0.0010 kJ g À1 , respectively, in full accordance with the calculated trend. Our findings provide an explanation for the well-known, but poorly understood solvent exchange phenomenon.

The unusual temperature behavior of the electron spin resonance (ESR) spectra and magnetic properties are experimentally observed in copper(II) complexes with a dendritic ligand based on the Boltorn H30 polymer (Perstorp Specialty Chemicals AB, Sweden) functionalized with fumaric acid residues in a molar ratio of 1:6. The ESR spectra at low temperatures show signs of transition to higher spin states at temperatures below 8–10 K, and the temperature dependences of the integral ESR signal intensities and magnetic susceptibility show the positive deviation from the Curie–Weiss law, thereby pointing to the presence of ferromagnetic exchange interactions in the system under study. The values of the exchange interaction parameters are calculated by quantum-chemical simulation of the possible structure of the copper(II) complex when assuming the formation of trinuclear coordination sites embedded in the hyperbranched polymer structure. The results of density functional theory calculations indicate the possibility of ferromagnetic exchange through carboxylate bridges in the trinuclear magnetic clusters, and the calculated values of the exchange interaction parameters make it possible to construct theoretical curves of the temperature dependence of the effective magnetic moment, which satisfactorily fit the experimental data, especially considering that polymers are characterized by disperse molecular weights and chemical structures.

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Quantum mechanical exchange effects in purely organic N,N′‐dioxy‐2,6‐diazaadamantane biradical derivatives with promesogenic substituents have been studied. To determine intermolecular exchange energies, packing conditions of the radical core units in layered liquid crystalline phases are simulated using the Gaussian 09 program. The broken symmetry approach gives J ≈ 7 cm−1 for intramolecular ferromagnetic exchange interactions between nitroxyl radical centers in one molecule. Both ferromagnetic and antiferromagnetic intermolecular interactions are possible in this kind of systems according to the obtained calculation results. Depending on the mutual positioning and orientation of molecules, the intermolecular antiferromagnetic exchange constant can reach a value of −50 cm−1, and the intermolecular ferromagnetic constant a value of 10 cm−1. The simultaneous presence of intramolecular and intermolecular exchange between spin‐carrying centers in this kind of supramolecularly ordered multispin systems is favorable for the formation of magnetically interacting chains and two‐dimensional networks. © 2016 Wiley Periodicals, Inc.

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