Chiroptical broad-range spectral analysis extending from UV to mid-IR was employed to study a family of Co­(II) N-(1-(aryl)­ethyl)­salicylaldiminato Schiff base complexes with pseudotetrahedral geometry associated with chirality-at-metal of the Δ/Λ type. While common chiral organic compounds have well-separated absorption and circular dichroism spectra (CD) in the UV/vis and IR regions, chiral Co­(II) complexes feature an almost unique continuum of absorption and CD bands, which cover in sequence the UV, visible, near-IR (NIR), and IR regions of the electromagnetic spectrum. They can be collected in a single (chiro)­optical superspectrum ranging from the UV (230 nm, 5.4 eV) to the mid-IR (1000 cm–1, 0.12 eV), which offers a fingerprint of the structure and stereochemistry of the metal complexes. Each region of the superspectrum contributes to one piece of information: the NIR-CD region, in combination with TDDFT calculations, allows a reliable assignment of the metal-centered chirality; the UV-CD region facilitates the analysis of the Δ/Λ diastereomeric equilibrium in solution; and the IR-VCD region contains a combination of low-lying metal-centered electronic states (LLES) and ligand-centered vibrations and displays characteristically enhanced and monosignate VCD bands. Circular dichroism in the NIR and IR regions is crucial to reveal the presence of d–d transitions of the Co­(II) core which, due to the electric-dipole forbidden character, would be otherwise overlooked in the corresponding absorption spectra.

The selenoether-functionalized imidazolium salt N-[(phenylseleno)­methylene)]-N′-methylimidazolium chloride (LH+Cl–) was transformed into the metal–carbene complexes [AgCl­(L)], [AuCl­(L)], [PdCl2(L)], and [PtCl2(L)] by the reaction with Ag2O and an additional transmetalation reaction of [AgCl­(L)] with [(THT)­AuCl], [(COD)­PdCl2], and [(COD)­PtCl2], respectively (THT = tetrahydrothiophene, COD = cyclooctadiene). The compound [AuI2Cl­(L)] was prepared by oxidation of [AuCl­(L)] with elemental iodine. The microwave-assisted decomposition of [PdCl2(L)] in the ionic liquid 1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ([BMIm]­NTf2) or in propylene carbonate led to the formation of Pd17Se15 nanoparticles of 51 ± 17 or 26 ± 7 nm diameter, respectively. The decomposition of the platinum complex resulted in either small Pt clusters around 1 nm size from the ionic liquid suspension or Pt nanoparticles of 3 ± 1 nm diameter in propylene carbonate. High-resolution X-ray photoelectron spectroscopy (HR-XPS) and 13C cross-polarization magic-angle spinning (CP MAS) NMR indicated that the surface of Pt clusters and crystalline Pt nanoparticles is formed by an amorphous Pt­(II)/Se shell and by carbene ligand residues.

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2-Substituted 3-ethynylquinoxaline chromophores can be readily synthesized by a consecutive activation-alkynylation-cyclocondensation (AACC) one-pot sequence in a three-component manner. In comparison with the previously published four-component glyoxylation starting from electron-rich π-nucleophiles, the direct activation of (hetero)aryl glyoxylic acids allows the introduction of substituents that cannot be directly accessed by glyoxylation. By introducing N,N-dimethylaniline as a strong donor in the 2-position, the emission solvatochromicity of 3-ethynylquinoxalines can be considerably enhanced to cover the spectral range from blue-green to deep red-orange with a single chromophore in a relatively narrow polarity window. The diversity-oriented nature of the synthetic multicomponent reaction concept enables comprehensive investigations of structure-property relationships by Hammett correlations and Lippert-Mataga analysis, as well as the elucidation of the electronic structure of the emission solvatochromic π-conjugated donor-acceptor systems by DFT and time-dependent DFT calculations with the PBEh1PBE functional for a better reproduction of the dominant charge-transfer character of the longest wavelength absorption band.

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