Hans‐Jörg Krüger

Temperature-Induced Spin-Transition in a Low-Spin Cobalt(II) Semiquinonate Complex†

Spin crossover and valence tautomerism are examples of processes that can be utilized as a basis for achieving molecular switches. Whereas the spin-crossover process is characterized by a temperature-, pressure-, or light-induced change of the electronic state of the metal ion to one with a different spin multiplicity, valence tautomerism entails an intramolecular redox reaction between a metal ion and a coordinated ligand, which, in a few instances, is accompanied by a change in the spin state of the metal ion. Various reported low-spin cobalt(III) catecholate complexes, which can be transformed into high-spin cobalt(II) semiquinonate complexes by raising the temperature, provide excellent examples of the latter process. In contrast, spin-crossover chemistry is dominated by octahedral iron(II) complexes with a FeN6 coordination sphere; [2] however, there are only very few known octahedral cobalt(II)-containing spin-crossover complexes. Herein we describe the first cobalt(II) semiquinonate complex that displays spin-crossover properties rather than valence tautomerism. The starting point of our investigation was the olive-green cobalt(III) 3,5-di-tert-butylcatecholate (dbc ) complex [Co(L-N4Me2)(dbc)](BPh4)·0.8MeCN·0.2Et2O (1) containing the dimethyl derivative of the tetraazamacrocyclic ligand 2,11diaza[3.3](2,6)pyridinophane (L-N4Me2) as coligand. This complex was obtained in 42 % yield by oxidation of the red cobalt(II) catecholate complex [Co(L-N4Me2)(dbc)] (prepared in situ from equimolar solutions of cobalt(II) perchlorate, L-N4Me2, and 3,5-di-tert-butylcatecholate) with ferrocenium tetrafluoroborate ([Fe(Cp)2](BF4); Cp = cyclopentadienyl), followed by a metathesis reaction with sodium tetraphenylborate (Scheme 1). In accordance with the description of 1 as a cobalt(III) catecholate complex, solutions and solids of this substance are diamagnetic. X-ray

Capture of CO2 by a Cationic Nickel(I) Complex in the Gas Phase and Characterization of the Bound, Activated CO2 Molecule by Cryogenic Ion Vibrational Predissociation Spectroscopy

We describe a systematic method for the preparation and spectroscopic characterization of a CO2 molecule coordinated to an activated bisphenoidal nickel(I) compound containing a tetraazamacrocyclic ligand in the gas phase. The resulting complex was then structurally characterized by using mass-selected vibrational predissociation spectroscopy. The results indicate that a highly distorted CO2 molecule is bound to the metal center in an η(2)-C,O coordination mode, thus establishing an efficient and rational method for the preparation of metal-activated CO2 for further studies using ion chemistry techniques.

Trapping of a Thiolate→Dibromine Charge‐Transfer Adduct by a Macrocyclic Dinickel Complex and Its Conversion into an Arenesulfenyl Bromide Derivative

Stuck on sulfur: The first transition-metal complexes with S-Br units are surprisingly stable. Solid 3 is stable for at least six months and under vacuum solid 2 does not lose Br(2). The formation of the first structurally characterized transition-metal arenesulfenyl bromide complex 3 occurs with a change of the spin ground state from S = 2 to S = 0.

Adsorption of I2 by Macrocyclic Polyazadithiophenolato Complexes Mediated by Charge-Transfer Interactions†

The macrocyclic complex [Ni2(L)(OAc)]ClO4 (1) adsorbs up to 17 molar equivalents (>270 wt%) of iodine, although it does not exhibit permanent porosity. Vibrational spectroscopic and crystallographic studies reveal that two I2 molecules are captured by means of thiophenolate→I2 charge-transfer interactions, which enable the diffusion and sorption of further I2 molecules in a polyiodide-like network. The efficient sorption and desorption characteristics make this material suitable for accommodation, sensing, and slow release of I2.

Bromidotetra­kis­(2-ethyl-1H-imidazole-κN3)copper(II) bromide

The CuII ion in the title molecular salt, [CuBr(C5H8N2)4]Br, is coordinated in a square-pyramidal geometry by four N atoms of imidazole ligands and one bromide anion in the apical position. In the crystal, the ions are linked by N—H⋯Br hydrogen bonds involving both the coordinating and the free bromide species as acceptors. A C—H⋯Br interaction is also observed. Overall, a three-dimensional network results.