Hydrogen-Bonding Motifs in MS2N2H Metallacycles: A Crystallographic and Computational Study of [CpCoS2N2H][BF4

Abstract

The first preparation and full characterization of highly insoluble [{η5–Cp}CoS2N2H][BF4] is reported. Proof of structure and composition is established from a single-crystal X-ray diffraction experiment at 173 K, which determined a crystal structure containing two independent cations and two independent anions in the asymmetric unit. The site of protonation is the terminal N of the S–N–S–N2– ligand which is coordinated to cobalt in the metallacycle. The crystal lattice contains numerous interatomic interactions, of which the most important are formed from multiple hydrogen bonds that link four [{η5–Cp}CoS2N2H]+ ions and two [BF4]− ions into a tetrameric cluster. The second kind of [BF4]− is not involved in intermolecular bonding. Short S···S′ interactions link such tetramers into planes; the resulting double-layer planes are described by the (101) Miller planes. DFT calculations using the B3PW91/6-311+G(3df)(2p) and B3LYP/6-311+G(3df)(2p) methods are in excellent agreement with the structure of the title cation from crystallography. Comparison to newly calculated and literature-reported DFT calculations on the neutral starting material [{η5–Cp}CoS2N2] and to a recent low-temperature crystal structure of the latter shows that there are only minor changes (≤3%) in the bond lengths within the CoS2N2 ring upon protonation, whereas the bond angles change by up to 9%. The B3PW91 functional is shown to be superior to B3LYP for computing the molecular structures of these formally CoIII metallacycles.