Exploring the structure-property schemes in anion-π systems of d-block metalates

Excited-State Proton Transfer in a Photoacid-Based Crystalline Coordination Compound: Reversible Photochromism, Near-Infrared Photothermal Conversion, and Conductivity

By harnessing the power of coordination self-assembly, crystalline materials can act as carriers for photoacids. Unlike their solution-based counterparts, these photoacids are capable of altering the properties of the crystalline material under light and can even generate proton transfer in a solid-state environment. Due to the photoinduced proton transfer and charge transfer processes within this functional material, this crystal exhibits powerful absorption spanning the visible to near-infrared spectrum upon light irradiation. This feature enables reproducible, significant chromatic variation, near-infrared photothermal conversion, and photocontrollable conductivity for this photoresponsive material. The findings suggest that the synthesis of pyranine photoacid-based crystalline materials via coordination self-assembly can not only enhance light-harvesting efficiency but also enable excited-state proton transfer processes within solid crystalline materials, thereby maintaining and even improving the properties of photoacids.

Anion-π Interactions: What's in the Name?

The studies of the anion-π interactions advanced during the last two decades from the discussion of the mere existence of this counter-intuitive bonding to its utilization for anion recognition and transport, catalysis, and other applications. Yet, there are substantial differences in the interpretation of nature and the driving forces of anion-π bonding. Most surprisingly, there are still different opinions about the meaning of this term (i. e., which associations can be considered anion-π complexes). After a brief overview of the studies in this area (including early examples of such complexes), we suggested that anion-π bonding occurs when there is evidence of a net attraction between a (close-shell) anion and the face of an electrophilic π-system. This definition encompasses fundamentally similar supramolecular complexes comprising diverse π-systems and anions and its general acceptance would facilitate a discussion of the nature and distinct driving forces of this fascinating interaction.

Crystallographic Aspects, Photophysical Properties, and Theoretical Survey of Tetrachlorometallates of Group 12 Metals [Zn(II), Cd(II), and Hg(II)] with a Triply Protonated 2,4,6-Tris(2-pyridyl)-1,3,5-triazine Ligand

Zn(II) (complex 1), Cd(II) (complex 2), and Hg(II) (complex 3) complexes have been synthesized using a triply protonated tptz (H₃tptz³⁺) ligand and characterized mainly by single-crystal X-ray analysis. The general formula of all of the complexes is (H₃tptz)³⁺·Cl^-·[MCl₄]^2-·nH₂O (where n = 1, 1.5, and 1.5 for complexes 1, 2, and 3, respectively). The crystallographic analysis reveals that the anion···π, anion···π⁺, and several hydrogen bonding interactions play a fundamental role in the stabilization of the self-assembled architectures that in turn help to enhance the dimensionality of all of the complexes. In addition, Hirshfeld surfaces and fingerprint plots have been deployed here to visualize the similarities and differences in hydrogen bonding interactions in 1-3, which are very important in forming supramolecular architectures. A density functional theory (DFT) study has been used to analyze and rationalize the supramolecular interactions by using molecular electrostatic potential (MEP) surfaces and combined QTAIM/NCI plots. Then, the device parameters for the complexes (1-3) have been thoroughly investigated by fabricating a Schottky barrier diode (SBD) on an indium tin oxide (ITO) substrate. It has been observed that the device made from complex 2 is superior to those from complexes 1 and 3, which has been explained in terms of band gaps, differences in the electronegativities of the central metal atoms, and the better supramolecular interactions involved. Finally, theoretical calculations have also been performed to analyze the experimental differences in band gaps as well as electrical conductivities observed for all of the complexes. Henceforth, the present work combined supramolecular, photophysical, and theoretical studies regarding group 12 metals in a single frame.

Magnetic interactions controlled by light in the family of Fe(II)-M(IV) (M = Mo, W, Nb) hybrid organic-inorganic frameworks

Three new hybrid organic-inorganic frameworks employing octacyanidometallates and 4,4'-bypiridine dioxide (4,4'-bpdo) as bridging molecules were prepared and characterized. The three-dimensional coordination frameworks {[Fe^II(μ-4,4'-bpdo)(H₂O)₂]₂[M^IV(CN)₈]·9H₂O}_n (Fe2Mo, Fe2W and Fe2Nb; M = Mo, W and Nb) are composed of cyanido-bridged chains, which are interconnected by the organic linkers. Magnetic measurements for Fe2Nb show a two-step transition to the antiferromagnetic state, which results from the cooperation of antiferromagnetic intra- and inter-chain interactions. Fe2Mo and Fe2W, on the other hand, behave as paramagnets at 2 K because of the diamagnetic character of the corresponding octacyanidometallate(IV) building units. However, after 450 nm light irradiation they show transition to the metastable high spin Mo^IV or W^IV states, respectively, with distinct ferromagnetic intrachain spin interactions, as opposed to the antiferromagnetic ones observed in the Fe2Nb framework.