Supramolecular cis-"Bis(Chelation)" of [M(CN)6]3- (M = CrIII, FeIII, CoIII) by Phloroglucinol (H3PG).

Studies on molecular co-crystal type materials are important in the design and preparation of easy-to-absorb drugs, non-centrosymmetric, and chiral crystals for optical performance, liquid crystals, or plastic phases. From a fundamental point of view, such studies also provide useful information on various supramolecular synthons and molecular ordering, including metric parameters, molecular matching, energetical hierarchy, and combinatorial potential, appealing to the rational design of functional materials through structure-properties-application schemes. Co-crystal salts involving anionic d-metallate coordination complexes are moderately explored (compared to the generality of co-crystals), and in this context, we present a new series of isomorphous co-crystalline salts (PPh4)3[M(CN)6](H3PG)2·2MeCN (M = Cr, 1; Fe, 2; Co 3; H3PG = phloroglucinol, 1,3,5-trihydroxobenzene). In this study, 1-3 were characterized experimentally using SC XRD, Hirshfeld analysis, ESI-MS spectrometry, vibrational IR and Raman, 57Fe Mössbauer, electronic absorption UV-Vis-NIR, and photoluminescence spectroscopies, and theoretically with density functional theory calculations. The two-dimensional square grid-like hydrogen-bond {[M(CN)6]3-;(H3PG)2}∞ network features original {[M(CN)6]3-;(H3PG)4} supramolecular cis-bis(chelate) motifs involving: (i) two double cyclic hydrogen bond synthons M(-CN⋅⋅⋅HO-)2Ar, {[M(CN)6]3-;H2PGH}, between cis-oriented cyanido ligands of [M(CN)6]3- and resorcinol-like face of H3PG, and (ii) two single hydrogen bonds M-CN⋅⋅⋅HO-Ar, {[M(CN)6]3-;HPGH2}, involving the remaining two cyanide ligands. The occurrence of the above tectonic motif is discussed with regard to the relevant data existing in the CCDC database, including the multisite H-bond binding of [M(CN)6]3- by organic species, mononuclear coordination complexes, and polynuclear complexes. The physicochemical and computational characterization discloses notable spectral modifications under the regime of an extended hydrogen bond network.

Mining anion-aromatic interactions in the Protein Data Bank.

Mutual positioning and non-covalent interactions in anion-aromatic motifs are crucial for functional performance of biological systems. In this context, regular, comprehensive Protein Data Bank (PDB) screening that involves various scientific points of view and individual critical analysis is of utmost importance. Analysis of anions in spheres with radii of 5 Å around all 5- and 6-membered aromatic rings allowed us to distinguish 555 259 unique anion-aromatic motifs, including 92 660 structures out of the 171 588 structural files in the PDB. The use of a scarcely exploited (x, h) coordinate system led to (i) identification of three separate areas of motif accumulation: A - over the ring, B - over the ring-substituent bonds, and C - roughly in the plane of the aromatic ring, and (ii) unprecedented simultaneous comparative description of various anion-aromatic motifs located in these areas. Of the various residues considered, i.e. aminoacids, nucleotides, and ligands, the latter two exhibited a considerable tendency to locate in region Avia archetypal anion-π contacts. The applied model not only enabled statistical quantitative analysis of space around the ring, but also enabled discussion of local intermolecular arrangements, as well as detailed sequence and secondary structure analysis, e.g. anion-π interactions in the GNRA tetraloop in RNA and protein helical structures. As a purely practical issue of this work, the new code source for the PDB research was produced, tested and made freely available at https://github.com/chemiczny/PDB_supramolecular_search.

Engineering of the XY Magnetic Layered System with Adeninium Cations: Monocrystalline Angle-Resolved Studies of Nonlinear Magnetic Susceptibility.

An original example of modular crystal engineering involving molecular magnetic {CuII[WV(CN)8]}- bilayers and adeninium cations (AdeH+) toward the new layered molecular magnet (AdeH){CuII[WV(CN)8]}·2H2O (1) is presented. 1 crystallizes within the monoclinic C2 space group (a = 41.3174(12), b = 7.0727(3), c = 7.3180(2) Å, ß = 93.119(3)°, and V = 2135 Å3). The bilayer topology is based on a stereochemical matching between the square pyramidal shape of CuII moiety and the bicapped trigonal prismatic shape of [WV(µ-CN)5(CN)3], and the separation between bilayers is significantly increased (by ∼50%; from ca. 9.5 to ca. 14.5 Å) compared to several former analogues in this family. This was achieved via a unique combination of (i) a 1D ribbonlike hydrogen bond system {AdeH+···H2O···AdeH+···}∞ exploiting planar water-assisted Hoogsteen···Sugar synthons with (ii) parallel 1D π-π stacks {AdeH+···AdeH+}∞. In-plane 2D XY magnetism is characterized by a Tc close to 33 K, Hc,in-plane = 60 Oe, and Hc,out-of-plane = 750 Oe, high values of in-plane γ critical exponents (γb = 2.34(6) for H||b and γc = 2.16(5) for H||c), and a Berezinskii-Kosterlitz-Thouless (BKT) topological phase transition, deduced from crystal-orientation-dependent scaling analysis. The obtained values of in-plane ν critical exponents, νb = 0.48(5) for H||b and νc = 0.49(3) for H||c, confirm the BKT transition (νBKT = 0.5). Full-range angle-resolved monocrystalline magnetic measurements supported by dedicated calculations indicated the occurrence of nonlinear susceptibility performance within the easy plane in a magnetically ordered state. We refer the occurrence of this phenomenon to spontaneous resolution in the C2 space group, a tandem not observed in studies on previous analogues and rarely reported in the field of molecular materials. The above magneto-supramolecular strategy may provide a novel means for the design of 2D molecular magnetic networks and help to uncover the inherent phenomena.

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

Anion-π based compounds, materials, and processes have gained significant interest due to the diversity of their aesthetic non-covalent synthons, and thanks to their significance in biological systems, catalytic processes, anion binding and sensing, or the supramolecular organization of hierarchical architectures. While systems based on typical inorganic anions or organic residues have been widely reviewed in recent years, those involving anionic d metal comlexes as the main components have been treated with a rather secondary interest. However, actively exploring the new systems of the latter type we have recognized systematic advances in the field. As a result, in the current review we describe the landscape that has recently emerged. Focusing on the established groups of π-acidic species, i.e. polycarbonitirles, polyazines, polyazine N-oxides, diimide derivatives, fluoroarenes, and nitroarenes, we explore and discuss anion-π crystal engineering together with the structure-property schemes important from the standpoint of charge transfer (CT) and electron transfer (ET), magnetism, luminescence, reactivity and catalysis, and the construction of core-shell crystalline composites.

Binding of anionic Pt(ii) complexes in a dedicated organic matrix: towards new binary crystalline composites.

The square-planar [PtX4]2- complexes (X = Cl, Br) were successfully incorporated into preprogrammed hybrid organic-inorganic systems, exploiting their expected strong anion-π interactions with π-acidic hexaazaphenylenehexacarbonitrile, HAT(CN)6. The formation and properties of {[PtCl4]2-; HAT(CN)6} aggregates in MeCN solution were evaluated based on their UV-Vis spectra to reveal the approximate binding constant KCT = 7.9(2) × 102 dm3 mol-1, molar absorption coefficient εCT = 1.47(2) × 103 dm3 mol-1 cm-1, extent of electronic coupling HCT = 2.18 × 103 cm-1, and electron delocalization α2 = 1.75 × 10-2 (α = 0.13). Strong [PtCl4]2-HAT(CN)6 interactions in such adducts were also confirmed by the distinct shifts |Δδiso| = 0.4 ppm of 13C NMR peaks, when compared to the π-acid alone. The crystal structures of the resulting (PPh4)2[PtX4][HAT(CN)6]·3MeCN (1-Cl- and 1-Br-) solids are isomorphous with (PPh4)2[Pt(CN)4][HAT(CN)6]·3MeCN (1-CN-) reported by us previously. The halogenoplatinates occupy exactly the same nodes in the supramolecular network as cyanoplatinate, forming stacked {[PtX4]2-;HAT(CN)6}∞ columns that are stabilized by [PPh4]+ cations. However, contrary to the pale yellow coloration of the [Pt(CN)4]2-/HAT(CN)6 systems, currently the dark violet or dark green coloration of solutions and crystalline phases were noted owing to the intense absorption in almost the whole visible region. DFT calculations reproduced the UV-Vis spectroscopic characteristics and linked it with the enhanced charge-transfer of the [PtX4]2-HAT(CN)6 electronic interactions. Based on the isomorphism of all three (PPh4)2[PtL4][HAT(CN)6]·3MeCN congeners we constructed and characterized the unprecedented, first ever anion-π-based binary rod-like core-shell crystalline composites 1-X@1-CN.