The CFH group, a potential surrogate for the OH group, can act as an unusual hydrogen bond donor, as confirmed by crystallographic, spectroscopic, and computational methods. Here, we demonstrate the bioisosterism of the OH and CFH groups and the important roles of CF-H···O hydrogen bonds in influencing intermolecular interactions and conformational preferences. Experimental evidence, corroborated by theory, reveals the distinctive nature of CFH hydrogen bonding interactions relative to their normal OH hydrogen bonding counterparts.
To elucidate the factors that impart selectivity for nitroxyl (HNO) over nitric oxide (NO), thiols, and H2S in metal-based fluorescent probes, we investigated five Cu(II)-cyclam (14-N4) derivatives. Upon exposure to NO gas at pH 7, no changes occur in the UV-vis spectra of any of the complexes. Addition of Angeli's salt to generate HNO promotes reduction of Cu(II) only in the case of [Cu(II)(14-N4-Ts)(OTf)2], which has the most positive reduction potential of the series. To gain insight into the observed reactivity, we prepared the Cu(II) complex of the mixed thia/aza 14-N2S2 ligand. [Cu(II)(14-N2S2)(OTf)2] reacts reversibly with HNO at pH 7, although nonselectively over thiols and H2S. The recurrent sensing of HNO uncovered with the study of Cu(II) azamacrocyclic complexes is a remarkable feature that opens the door for the design of a new generation of metal-based probes.
A new transition-metal-free mode for the catalytic reduction of carbon dioxide via bidentate interaction has been developed. In the presence of Li2[1,2-C6H4(BH3)2], CO2 can be selectively transformed to either methane or methanol, depending on the reducing agent. The bidentate nature of binding is supported by X-ray analysis of an intermediate analogue, which experiences special stabilization due to aromatic character in the bidentate interaction. Kinetic studies revealed a first-order reaction rate. The transformation can be conducted without any solvent.
Critically discussing and, if necessary, questioning results presented by other researchers has always been a vitally important process in science. Only through fruitful discourse does science arrive at broadly accepted hypotheses that finally become what we accept as scientific truth. In the spirit of this time-honored tradition, we have examined the crystal structure as well as X-ray diffraction data of the proposed compound [K(crypt-222)] CF , which has recently been published. We arrived at the conclusion that the claim of the authors to have successfully and unambiguously characterized the ionic [K(crypt-222)] CF through single-crystal X-ray diffraction is not sustainable. Even though it is possible that the original authors have indeed encountered the proposed species, the purpose of this report is to point out that the original authors cannot use the presented crystallographic data and model as proof for the existence of [K(crypt-222)] CF . The reason for our conclusion is two-fold: firstly, the crystal structure was not refined to established standards of good crystallographic practice and secondly, even if best practices of structure determination are employed, the submitted diffraction data do not allow establishing conclusively the true nature of the compound at hand. Recognizing that this gives charge unbalance we have not resolved, we nevertheless suggest an alternative molecular model, [K(crypt-222)]⋅CHF , to demonstrate the ambiguity of the diffraction data submitted by the original authors. However, because of this ambiguity, it is important to point out that the purpose of this report is not (and cannot be) the determination of the true nature of the compound at hand; we would merely like to demonstrate that an alternative interpretation of the original diffraction data is possible and, hence, that the conclusion drawn by the original authors is not unambiguously supported by their own data.
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