Formation of 1 D and 3 D Coordination Polymers in the Solid State Induced by Mechanochemical and Annealing Treatments: Bis(3-cyano-pentane-2,4-dionato) Metal Complexes

N Donor substituted acetylacetones – versatile ditopic ligands

Acetylacetone (2,4-pentanedione) derivatives with N donor substituents represent ditopic ligands with coordination sites of distinctly different Pearson hardness. Deprotonation of the acetylacetone (Hacac) moiety leads to O,O′ chelating monoanionic (acac) ligands suitable for coordination to hard cations. The softer N donor site(s) preferably act as nucleophiles towards softer partners. When the organic molecules are employed as linkers and coordinate via either site, they are often selective and allow to synthesize well-ordered heterometallic solids. This review addresses the derivatives of 17 pentanediones with nitrile, pyridyl and pyrazolyl moieties as N donor substituents, with an emphasis on structurally characterized compounds. Depending on the N donor substituents and the cations, O,O′ or N coordination will dominate. The nitrile-substituted compounds essentially behave as acetylacetones; they may easily O,O′ coordinate to a wide range of cations whereas N coordination is limited to AgI, CuI or, in the case of less soft cations, to longer and presumably weaker contacts, e.g. to the more distant sites in Jahn–Teller distorted CuII. In contrast, pyridyl-substituted pentanediones act as N donor ligands, regardless whether their (H)acac site is chelating a cation or not. The still scarcely explored pyrazolyl derivative shows the most complex coordination pattern: it may be deprotonated both at the acetylacetone and the pyrazol site, the latter affording N,N′ bridging ligands. In addition to N donor nucleophilicity, the distance between the alternative coordination sites and their mutual orientation are relevant for crystal engineering applications.

Exploring mechanochemistry to turn organic bio-relevant molecules into metal-organic frameworks: a short review

Mechanochemistry is a powerful and environmentally friendly synthetic technique successfully employed in different fields of synthetic chemistry. Application spans from organic to inorganic chemistry including the synthesis of coordination compounds. Metal-organic frameworks (MOFs) are a class of compounds with numerous applications, from which we highlight herein their application in the pharmaceutical field (BioMOFs), whose importance has been growing and is now assuming a relevant and promising domain. The need to find cleaner, greener and more energy and material-efficient synthetic procedures led to the use of mechanochemistry into the synthesis of BioMOFs.

Synthesis of a One-Dimensional Coordination Polymer of Nickel(II) Complex with a β-Oxodithioester Ligand

Bis-[methyl-1-hydroxy-1-cyclopentene-2-dithiocarboxylate-O,S]nickel(II) 1 was prepared starting from methyl 2-hydroxycyclopent-1-encarbodithioate ligand (CPDT) and Ni(II), and catena-[(μ2-4,4′-Bipyril)-bis-(methyl-2-hydroxy-1-cyclopentene-2-dithiocarboxylate-O,S)]nickel(ΙΙ) 2 was prepared in good yields from 1 plus 4,4′-bipyridyl (bpy) by shish-kebab methodology. The structure of 1 was confirmed by FTIR, elemental analysis, 1H NMR, UV–vis in chloroform solution and in solid, XPS, and PXRD. Compound 2 was characterized by FTIR, elemental analysis, UV–vis in chloroform solution, and in solid, XPS, PXRD, ESR, and solid state magnetization measurements. The structure of the polymer was established mostly by PXRD, ESR, and magnetization.

Mechanochemical and thermal formation of 1H-benzotriazole coordination polymers and complexes of 3d-transition metals with intriguing dielectric properties

Liquid-assisted grinding (LAG) reactions have been successfully applied to achieve a series of complexes and coordination polymers based on divalent 3d-transition metal chlorides (TM chlorides) and the aromatic ligand 1H-benzotriazole (BtzH). The obtained substances were investigated via single crystal X-ray, powder X-ray determination and simultaneous DTA/TG analysis as model compounds for structural and chemical influences on their dielectric properties. Depending on the synthesis method, different constitutions and structures are observed. Two polymorphous forms of the 1D polymer [MnCl2(BtzH)2] (1 and 2) as well as the complexes [ZnCl2(BtzH)2]·BtzH (3) and [CoCl2(BtzH)2]·BtzH (4) have been obtained as phase-pure bulk substances via the mechanochemical LAG route, and even single crystals are available. For comparison, thermal reactions were also carried out and have led to the formation of the neutral complexes: [CoCl2(BtzH)2] (5) and [CoCl2(BtzH)4]·4BtzH (6), [ZnCl2(BtzH)2] (7) and the anionic complex BtzH2[CoCl3BtzH] (8). In addition, thermal treatment of 3 yields the benzotriazolium salt {(BtzH)2H}Cl (9). The transition metal compounds were additionally analysed regarding their dielectric properties by frequency-dependent as well as temperature-dependent permittivity investigations. It is intriguing that compounds 1 and 3 show remarkably low dielectric constants and loss factors up to 50 °C highlighting them as potential "low-k materials".

Rapid mechanochemical synthesis of two new Cd(ii)-based metal–organic frameworks with high removal efficiency of Congo red

Two new three-dimensional porous Cd(ii)-based metal–organic frameworks, TMU-8 and TMU-9, with high performance in adsorption of Congo red.

Isomerization of a lanthanide complex using a humming top guest template: a solid-to-solid reaction

SbPh₃Cl₂is used to effect a dramatic rearrangement of the ligand sphere and “pancake bonding” in Ce(hfac)₃(5′-Br-pyDTDA)₂by forming a 2 : 1 host–guest complex.

Supramolecular concepts and new techniques in mechanochemistry: cocrystals, cages, rotaxanes, open metal-organic frameworks

Mechanochemical reactions effected by milling or grinding are an attractive means to conduct chemical reactions dependent on molecular recognition and to systematically explore different modes of molecular self-assembly. The natural relationship between milling mechanochemistry and supramolecular chemistry arises primarily from the ability to avoid bulk solvent, which simultaneously avoids limitations of solution-based chemistry, such as solubility, solvent complexation, or solvolysis, and makes the resulting process highly environmentally friendly. This tutorial review highlights the use of mechanochemistry for the synthesis of supramolecular targets in the solid state, such as molecular hydrogen- or halogen-bonded complexes, molecular and supramolecular cages, open frameworks and interlocked architectures. It is also demonstrated that the molecular self-assembly phenomena that are well-established in solution chemistry, such as reversible binding through covalent or non-covalent bonds, thermodynamic equilibration and structure templating, are also accessible in milling mechanochemistry through recently developed highly efficient methodologies such as liquid-assisted grinding (LAG) or ion- and liquid-assisted grinding (ILAG). Also highlighted are the new opportunities arising from the marriage of concepts of supramolecular and mechanochemical synthesis, including organocatalysis, deracemisation and discovery of new molecular recognition motifs.

(Pentane-2,4-dionato-κ2O,O′)(pyridin-2-amine-κN1)copper(II) and (pentane-2,4-dionato-κ2O,O′)(pyrimidin-2-amine-κN1)copper(II)

The title compounds, [Cu(C5H7O2)2(C5H6N2)], (I), and [Cu(C5H7O2)2(C4H5N3)], (II), were prepared by the reaction of bis(pentane-2,4-dionato-κ2O,O′)copper(II) with pyridin-2-amine and pyrimidin-2-amine, respectively. From a chemical point of view, it is interesting that no Schiff base formation was observed. The compounds are isostructural, with both having a square-pyramidal coordination of the CuIIatom and intramolecular N—H...O hydrogen bonding. The additional N atom of the pyrimidin-2-amine ligand is not involved in hydrogen bonding or in metal coordination. In the crystal structure, chelate rings are involved in π–π interactions and molecules of (I) are linked togetherviaN—H...O hydrogen bonds.

Systematic mechanochemical preparation of a series of coordination pillared layer frameworks

A detailed investigation into the mechanochemical synthesis of coordination pillared-layer frameworks (CPLs), particularly CPL-1, was carried out. In the case of CPL-1, a two-step reaction was observed (from the starting reactants to the final product). In the conventional solution process, no intermediate state was detected. We found that moisture is essential in both the reaction steps. After the final product was washed, it showed the same sorption ability as the product prepared from a solution process. We further demonstrated the systematic preparation of other CPLs (CPL-2, 3, 4, 5, and 15) by the mechanochemical method under humid conditions, even though some of the ligands are almost insoluble in water. Our findings indicate that mechanochemical synthesis is a promising alternative method for the systematic and large-scale production of PCPs. Its advantages include the following: reduced pollution, low cost, simplicity of the process, ease of handling, efficient reaction rate, selectivity, and the issue of low solubility of reactants is overcome.

Synthesis of azines in solid state: reactivity of solid hydrazine with aldehydes and ketones

Highly conjugated azines were prepared by solid state grinding of solid hydrazine and carbonyl compounds such as aldehydes and ketones, using a mortar and a pestle. Complete conversion to the azine product is generally achieved at room temperature within 24 h, without using solvents or additives. The solid-state reactions afford azines as the sole products with greater than 97% yield, producing only water and carbon dioxide as waste.