Coordination polymer changing its magnetic properties and colour by thermal decomposition: synthesis, structure and properties of new thiocyanato iron(ii) coordination polymers based on 4,4′-bipyridine as ligand

Metal-Organic Framework Flowers as a Naked-Eye Colorimetric Indicator of Trace Water

Convenient and sensitive trace water indication is of great significance in various industrial processes. Here, a flower-like metal-organic framework Cu-FMM is assembled from ultrathin nanosheets that change its coordination structure reversibly with the capture and loss of water molecules, enabling sensitive trace water naked-eye colorimetric indication ability. A recognizable black/yellow color change can be observed when the dried Cu-FMM is exposed to the atmosphere or solvent with trace water as low as RH 3% and a water content of 0.25‰ (v/v) and further enables potential trace water imaging applications. The excellent accessibility of the multi-scale pore structure of Cu-FMM contributes to a fast response time of 3.8 s with good reversibility (>100 cycles), outperforming traditional coordination polymer humidity sensors. The present study provides new inspirations for the design of sensitive and applicable naked-eye water indicator materials that are applicable to in situ and continuous monitoring in industrial processes.

Photosynthesis of a Dihydroimidazopyridine Chelate Shines Light on the Reactions of a Photoactivated Iron(III) Complex with O2

The high-spin (S = ⁵/₂) meridional diastereoisomer of [Fe^III(tpena)]²⁺ (tpena = N,N,N'-tris(2-pyridylmethyl)ethylendiamine-N'-acetate), mer-[Fe(tpena)]²⁺, undergoes photolytic CO₂ release to produce an iron(II) intermediate of a radical dihydroimidazopyridine ligand (L^•). The structure of this unprecedented transient iron(II)(L^•) complex is supported by UV-vis and Mössbauer spectroscopies, DFT calculations, as well as the X-ray structural characterization of an μ-oxo iron(III) complex of the oxidized derivative of L^•, namely, [Fe^III₂O(Cl)₂(L⁺)₂](ClO₄)₄(MeCN)₂ (L⁺ = 2-(2-(bis(pyridin-2-ylmethyl)amino)ethyl)-2,3-dihydro-1H-imidazo[1,5-a]pyridin-4-ium). [Fe^III₂O(Cl)₂(L⁺)₂]⁴⁺ is obtained only in the absence of O₂. Under aerobic conditions, O₂ will intercept the iron(II)(L^•) complex to form a putative Fe(III)-alkylperoxide complex which cascades to an iron(II) complex of SBPy3 (SBPy3 = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-aldimine). Thus, through different oxidative pathways, the unknown ligand L⁺ or SBPy3 forms by loss of a one-carbon-atom or a two-carbon-atom unit, respectively, from the glycyl arm of tpena. Acceleration of the photodecarboxylation step is achieved by addition of thiocyanate because of transient formation of a more photoreactive NCS^- adduct of [Fe(tpena)]²⁺. This has allowed for kinetic observation of the reaction of [Fe^II(L^•)]²⁺ with O₂ which is, unexpectedly, promoted also by light. We propose that this corresponds to the energy needed for the conversion of the ring-closed radical ligand L^• to a ring-opened tautomer to allow for O₂ insertion between the C and Fe atoms of the iron(II) complex.

Metal-Organic Framework Magnets

Metal-organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal-organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal-organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal-organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal-organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal-organic magnet research that laid the foundation for structurally characterized metal-organic framework magnets. Sections 3 and 4 then outline the literature of metal-organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal-organic framework magnets while maintaining structural integrity and additional function.

3-Cyanopyridine as a bridging and terminal ligand in coordination polymers

Crystal structures of [M^IIBr₂(3-CNpy)_x]_(n) with M = Mn, Fe, Co, Ni and x = 1, 2, 4 were determined by powder diffraction. For x = 1, the 3-cyanopyridine ligand is bridging two metal atoms.

4-Cyanopyridine, a versatile mono- and bidentate ligand. Crystal structures of related coordination polymers determined by X-ray powder diffraction

4-Cyanopyridine (4-CNpy) as a monodentate ligand in single or double chains or as a bidentate ligand in two-dimensional networks.

Bis(4-pyridyl)mercury – a new linear tecton in crystal engineering: coordination polymers and co-crystallization processes

Three new coordination polymers have been obtained using bis(4-pyridyl)mercury (py₂Hg) as a spacer: [Cu(Hmea)₂(py₂Hg)](ClO₄)₂·2(py₂Hg) (1), [Cu₂(pa)₂(py₂Hg)(ClO₄)₂]·0.5(py₂Hg)·H₂O (2), and [Cu₂(pa)₂(py₂Hg)₂](BF₄)₂ (3) (Hmea = monoethanolamine; Hpa = propanolamine).

Dynamic magnetic MOFs

In this review we combine the use of coordination chemistry with the concepts of molecular magnetism to design magnetic Metal-Organic Frameworks (MOFs) in which the crystalline network undergoes a dynamic change upon application of an external stimulus. The various approaches so far developed to prepare these kinds of chemically or physically responsive MOFs with tunable magnetic properties are presented.

catena-Poly[[bis-(methanol-κO)bis-(thio-cyanato-κN)cobalt(II)]-μ-1,3-bis-(pyridin-4-yl)propane-κN,N']

The asymmetric unit of the title compound, [Co(NCS)₂(C₁₃H₁₄N₂)(CH₃OH)₂], consists of one cobalt(II) cation located on a center of inversion, one half of a 1,3-bis­(pyridin-4-yl)propane ligand located on a twofold rotation axis, as well as one thio­cyanate anion and one methanol mol­ecule in general positions. The cobalt(II) cation is coordinated by two terminal N-bonded thio­cyanate anions and two N-bonded 1,3-bis­(pyridin-4-yl)propane ligands, as well as two O atoms of methanol mol­ecules in a slightly distorted octa­hedral coordination mode. Adjacent cations are connected into chains parallel to [10] by the bridging 1,3-bis­(pyridin-4-yl)propane ligands. These chains are connected through inter­molecular O—H⋯S hydrogen bonds between the methanol hy­droxy group and the terminal S atom of the thio­cyanate anion.

catena-Poly[[bis-[[bis-(3-amino-prop-yl)amine-κN,N',N''](thio-cyanato-κN)cadmium]-μ(4)-sulfato-κO,O:O',O'] methanol hemisolvate]

The asymmetric unit of the title compound, {[Cd₂(NCS)₂(SO₄)(C₆H₁₇N₃)₂]·0.5CH₃OH}_n, consists of two Cd²⁺ cations, two thio­cyanate and one sulfate anion, two bis­(3-amino­prop­yl)amine co-ligands and one methanol molecule with half-occupancy. Each Cd²⁺ cation is coordinated by four N atoms of one terminal N-bonded thio­cyanate anion and one bis­(3-amino­prop­yl)amine co-ligand, and by two O atoms of two symmetry-related sulfate anions, defining a slightly distorted octa­hedral coordination polyhedron. Each two Cd²⁺ cations are connected into dimers, which are located on centres of inversion and which are further μ-1,1:3,3-bridged via the sulfate anions into polymeric zigzag chains along the a axis.

[Bis(3-amino-prop-yl)amine-κN,N',N'']bis-(thio-cyanato-κN)cobalt(II)

The asymmetric unit of the title compound, [Co(NCS)(2)(C(6)H(17)N(3))], consists of one Co(2+) cation, two thio-cyanate anions and one bis-(3-amino-prop-yl)amine ligand, all in general positions. The cobalt cation is coordinated by five N atoms of two terminal N-bonded thio-cyanate anions and one bis-(3-amino-prop-yl)amine ligand, defining a slightly distorted square-pyramidal coordination polyhedron. The mol-ecules are held together in the crystal by weak N-H⋯S inter-actions.

Chloridotetra-pyridine-copper(II) dicyanamidate pyridine disolvate

In the crystal structure of the title compound, [CuCl(C₅H₅N)₄][N(CN)₂]·2C₆H₅N, the copper(II) cations are coordinated by one chloride anion and four N-bonded pyridine ligands into discrete complexes. The copper(II) cation shows a square-pyramidal coordination environment, with the chloride anion in the apical position. However, there is one additional chloride anion at 3.0065 (9) Å, leading to a disorted octa­hedral coordination mode for copper. The copper(II) cation, the chloride ligand and the central N atom of the dicyanamide anion are located on twofold rotation axes. Two pyridine solvent molecules are observed in general positions.

Poly[bis-(acetonitrile-κN)di-μ-thio-cyanato-κN,S;κS,N-nickel(II)]

In the title compound, [Ni(NCS)(2)(CH(3)CN)(2)](n), the Ni(II) cation is coordinated by two N-bonded and two S-bonded thio-cyanate anions, as well as two acetonitrile mol-ecules in an octa-hedral NiN(4)S(2) coordination mode. The asymmetric unit comprises one nickel cation, two thio-cyanate anions and two actonitrile mol-ecules. In the crystal, the Ni(II) cations are connected by bridging thio-cyanate anions into a three-dimensional coordination network.