The self-assembly of lanthanide ions with ditopic organic spacers results in the formation of complex tiling patterns that mimic the structural motifs of quasi-periodic 2D materials. The linking of trans-{LnI 2 } + nodes (Ln = Gd, Dy) by both closedshell and anion radicals of 4,4′-bipyridine affords rare examples of Archimedean tessellations in a metal−organic framework. We furthermore demonstrate the occurrence of sizable magnetic exchange interactions and slow relaxation of magnetization behavior in a complex tessellation pattern. The implementation of Archimedean tessellations in lanthanide(III) coordination solids couriers a strategy to design elusive quasi-periodic metal−organic frameworks with inimitable magnetic properties.T he design of complex and aperiodic two-dimensional tessellations in molecule-based materials constitutes a novel route to harvest physical properties, for instance, photonic, electronic, magnetic, and phononic characteristics, which are expected to be unparalleled compared to their periodic counterparts. 1−3 However, applications are elusive due to the severe scarcity of materials exhibiting the desired structural motifs. The two-dimensional dodecagonal quasicrystalline phase (Figure 1a, ddQC) is well-known in both hard and soft materials as well as in supramolecular networks. 4−6 In these system, the tessellation of triangles and squares, at a ratio of 4/√3 ≈ 2.3, leads to the disappearance of periodicity and the formation of local 12-fold rotational symmetry. Generally, quasicrystals are found in the vicinity of structurally related, periodic structures, and the ddQCs often co-occur with the periodic Archimedean tessellations (ATs, Figure 1b,c), which are termed quasicrystal approximants. 7 The sole example of a quasicrystal phase found in a metal−organic network structure
The true global potential energy minimum configuration of the formaldehyde dimer (CHO), including the presence of a single or a double weak intermolecular CH⋯O hydrogen bond motif, has been a long-standing subject among both experimentalists and theoreticians as two different energy minima conformations of C and C symmetry have almost identical energies. The present work demonstrates how the class of large-amplitude hydrogen bond vibrational motion probed in the THz region provides excellent direct spectroscopic observables for these weak intermolecular CH⋯O hydrogen bond motifs. The combination of concentration dependency measurements, observed isotopic spectral shifts associated with H/D substitutions and dedicated annealing procedures, enables the unambiguous assignment of three large-amplitude infrared active hydrogen bond vibrational modes for the non-planar C configuration of (CHO) embedded in cryogenic neon and enriched para-hydrogen matrices. A (semi)-empirical value for the change of vibrational zero-point energy of 5.5 ± 0.3 kJ mol is proposed for the dimerization process. These THz spectroscopic observations are complemented by CCSD(T)-F12/aug-cc-pV5Z (electronic energies) and MP2/aug-cc-pVQZ (force fields) electronic structure calculations yielding a (semi)-empirical value of 13.7 ± 0.3 kJ mol for the dissociation energy D of this global potential energy minimum.
β‐Diketonates, such as acetylacetonate, are amongst the most common bidentate ligands towards elements across the entire periodic table and are considered wholly redox‐inactive in their complexes. Herein we show that complexation of 1,1,1,5,5,5‐hexafluoroacetylacetonate (hfac−) to CrII spontaneously affords CrIII and a reduced β‐diketonate radical ligand scaffold, as evidenced by crystallographic analysis, magnetic measurements, optical spectroscopy, reactivity studies, and DFT calculations. The possibility of harnessing β‐diketonates as electron reservoirs opens up possibilities for new metal–ligand concerted reactivity in the ubiquitous β‐diketonate coordination chemistry.
This work demonstrates how large-amplitude OH librational motion of H2O molecules directly reflects the microsolvation of organic compounds. The highly localized OH librational motion of the first solvating H2O molecule gives rise to a strong band origin νlib in the far-infrared spectral region, which is correlated quantitatively with the intermolecular hydrogen bond energy D0.
The high-resolution terahertz absorption spectrum of the large-amplitude intermolecular donor librational band ν of the homodimer (HCN) has been recorded by means of long-path static gas-phase Fourier transform spectroscopy at 207 K employing a highly brilliant electron storage ring source. The rovibrational structure of the ν band has the typical appearance of a perpendicular type band of a Σ-Π transition for a linear polyatomic molecule. The generated terahertz spectrum is analyzed employing a standard semi-rigid linear molecule Hamiltonian, yielding a band origin ν of 119.11526(60) cm together with values for the excited state rotational constant B', the excited state quartic centrifugal distortion constant D' and the l-type doubling constant q for the degenerate state associated with the ν mode. The until now missing donor librational band origin enables the determination of an accurate experimental value for the vibrational zero-point energy of 2.50 ± 0.05 kJ mol arising from the entire class of large-amplitude intermolecular modes. The spectroscopic findings are complemented by CCSD(T)-F12b/aug-cc-pV5Z (electronic energies) and CCSD(T)-F12b/aug-cc-pVQZ (force fields) electronic structure calculations, providing a (semi)-experimental value of 17.20 ± 0.20 kJ mol for the dissociation energy D of this strictly linear weak intermolecular CHN hydrogen bond.
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