Šembera, F.; Plutnar, J.; Higelin, A.; Janoušek, Z.; Císařová, I.; Michl, J. “Metal Complexes with Very Large Dipole Moments: the Anionic Carborane Nitriles 12-NC-CB11X11− (X = H, F, CH3) as Ligands on Pt(II) and Pd(II)”, Inorg. Chem. 2016, 55, 3797.
Abstract: The anionic nitriles 1-R-12-NC-CB11H10− (R = H, CH3, I, COOH), 12-NC-1-H-CB11Me10−, and 12-NC-1-H-CB11F10− have been prepared and three of them were examined for complex formation with (Et3P)2Pt(II) and (Et3P)2Pd(II). Several stable internally charge-compensated zwitterionic complexes were obtained and characterized. RI-BP86/SV(P) calculations suggest that their dipole moments exceed 20 Debye. An attempt to measure the dipole moments in solution failed due to insufficient solubility in solvents of low polarity.
Givelet, C. C.; Dron, P. I.; Wen, J.; Magnera, T. F.; Zamadar, M.; Čépe, K.; Fujiwara, H.; Shi, Y.; Tuchband, M. R. K.; Clark, N.; Zbořil, R.; Michl, J. “Challenges in the Structure Determination of Self-Assembled Metallacages: What Do Cage Cavities Contain, Internal Vapor Bubbles or Solvent and/or Counterions?”, J. Am. Chem. Soc. 2016, 138, 6676.
Abstract: Proving the structures of charged metallacages obtained by metal ion coordination-driven solution self-assembly is challenging and the common use of routine NMR spectroscopy and mass spectrometry is unreliable. Carefully determined diffusion coefficients from diffusion-ordered proton magnetic resonance (DOSY NMR) for six cages of widely differing sizes lead us to propose a structural reassignment of two molecular cages from a previously favored trimer to a pentamer or hexamer, and another from a trimer to a much higher oligomer, possibly an intriguing tetradecamer. In the former case, strong support for the reassignment to a larger cage is provided by an observation of a slow reversible transformation of the initially formed cage into a smaller but spectrally very similar one upon dilution. In the latter case, freeze-fracture transmission electron micrographs demonstrate that at least some of the solutions are colloidal, and high-resolution electron transmission and atomic force microscopy images are compatible with a tetradecamer but not a trimer. Comparison of solute partial molar volumes deduced from measurement of solution density with volumes anticipated from molecular models argues strongly against the presence of large voids (solvent vapor bubbles) in cages dissolved in nitromethane. The presence of bubbles was previously proposed in an attempt to account for the bilinear nature of the Eyring plot of the rate constant for pyridine ligand edge exchange reaction in one of the cages and for the unusual activation parameters in the high-temperature regime. An alternative interpretation is proposed now.
Urbanová, V.; Karlický, F.; Matěj, A.; Šembera, F.; Janoušek, Z.; Perman, J. A.; Ranc, V.; Čépe, K.; Michl, J.; Otyepka, M.; Zbořil, R. “Fluorinated Graphenes as Advanced Biosensors - Effect of Fluorine Coverage on Electron Transfer Properties and Adsorption of Biomolecules”, Nanoscale 2016, 8, 12134.
Abstract: Graphene derivatives are promising materials for the electrochemical sensing of diverse biomolecules and development of new biosensors owing to their improved electron transfer kinetics compared to pristine graphene. Here, we report complex electrochemical behavior and electrocatalytic performance of variously fluorinated graphene derivatives prepared by reaction of graphene with a nitrogen-fluorine mixture in an autoclave under increased pressure (2 bars). The fluorine content was simply controlled by varying the reaction time and temperature. The study revealed that electron transfer kinetics and electrocatalytic activity of CFx strongly depends on the degree of fluorination. The versatility of fluorinated graphene as a biosensor platform was demonstrated by cyclic voltammetry for different biomolecules playing essential roles in physiological processes, i.e. NADH, ascorbic acid and dopamine. Importantly, the highest electrochemical performance, even higher than pristine graphene, was obtained for fluorinated graphene with the lowest fluorine content (CF0.084) due to its high conductivity and enhanced adsorption properties combining pi-pi stacking interaction with graphene regions with hydrogen-bonding interaction with fluorine atoms.
Fogarty, H. A.; Chen, X.; Wang, B.; Michl, J. “Controlling n-Oligosilane Conformation by Stretching on a Staffane Rack”, in Efficient Methods for Preparing Silicon Compounds, Roesky, H. W., Ed.; Elsevier: New York, NY, 2016, p. 355.
Craig, P. R.; Havlas, Z.; Trujillo, M.; Rempala, P.; Kirby, J. P.; Miller, J. R.; Noll, B. C.; Michl, J. “Electronic Spectra of the Tetraphenylcyclobutadienecyclopentadienylnickel(II) Cation and Radical”, J. Phys. Chem. A 2016, 120, 3456.
Abstract: Properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF4− anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical, whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ~0.1 V upon going from 1 to 1a. Unsuccessful attempts to prepare several other aryl substituted derivatives of 1 by the classical synthetic route are described in the Supporting Information.