Thermal Decomposition Reactions as Tool for the Synthesis of New Metal Thiocyanate Diazine Coordination Polymers with Cooperative Magnetic Phenomena

Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)2(pyrimidine)2]n (2) which is isotypic to [Co(NCS)2(pyrimidine)2]n (1) reported recently. In the crystal structure, the Ni2+ ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)2(pyrimidine)]n (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni2+ ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two S atoms of μ-1,3 bridged thiocyanato anions, which conntect these chains into layers, within a slightly distorted octahedral geometry. On heating compounds 1 and 2 transform quantitatively into the ligand-deficient 1:1 Ni compound 4 and its isotypic Co compound 3. If nickel and cobalt thiocyanate are reacted with an excess of pyrimidine in a solvent-free reaction, discrete ligand-rich 1:4 complexes of composition [M(NCS)2(pyrimidine)4] (M = Co 5 and Ni 6) are obtained, which could be determined by single crystal structure analysis. In their crystal structure the metal ions are coordinated by four terminal bonded pyrimidine ligands and two terminal N-bonded thiocyanato anions. For the ligand-rich 1:2 and ligand-deficient 1:1 compounds magnetic measurements were performed, which reveal different magnetic properties: The 1:2 compounds show a ferromagnetic and the 1:1 compounds an antiferromagnetic ordering at lower temperatures

Dimorphism of a New CuI Coordination Polymer:Synthesis, Crystal Structures and Properties of Catena[CuI(2-Iodopyrazine-N)] and Poly[CuI(μ₂-2-Iodopyrazine-N,N‘)]

Two modifications of the new copper(I) iodide coordination polymer CuI(2-iodopyrazine) were obtained by the reaction of CuI and 2-iodopyrazine in acetonitrile. During this reaction, intensely yellow crystals of form I appear first which transform within several minutes to intensely red crystals of form II which is the thermodynamically most stable form at room temperature. In catena[CuI(2-iodopyrazine-N)] (form I; a = 4.1830 (6) Å; b = 10.814 (1) Å; c = 17.961 (4) Å; V = 812.5 (2) Å3; orthorhombic; P212121; Z = 4), corrugated CuI double chains are found in which each copper atom is coordinated by one additional 2-iodopyrazine ligand. In poly[CuI(μ-2-iodopyrazine-N,N‘)] (form II; a = 4.2679 (5) Å; b = 13.942 (2) Å; c = 13.017 (2) Å; b = 92.64 (1)°; V = 773.76 (2) Å3; monoclinic; P21/c; Z = 4), CuI single chains occur which are connected via μ-N,N‘ coordination by the 2-iodopyrazine ligands to layers parallel to (010). The thermal behavior of both forms was investigated using simultaneous differential thermoanalysis, thermogravimetry, and mass spectrometry as well as differential scanning calorimetry and temperature resolved X-ray powder diffraction. On heating, both forms decompose to copper(I) iodide, and the decomposition temperature of form I is significantly lower than that of form II. From all experiments, there is no indication of a phase transition of one form into the other or for the formation of a phase with lower amine content

Dimorphism of a New CuI Coordination Polymer:Synthesis, Crystal Structures and Properties of Catena[CuI(2-Iodopyrazine-N)] and Poly[CuI(μ₂-2-Iodopyrazine-N,N‘)]

Two modifications of the new copper(I) iodide coordination polymer CuI(2-iodopyrazine) were obtained by the reaction of CuI and 2-iodopyrazine in acetonitrile. During this reaction, intensely yellow crystals of form I appear first which transform within several minutes to intensely red crystals of form II which is the thermodynamically most stable form at room temperature. In catena[CuI(2-iodopyrazine-N)] (form I; a = 4.1830 (6) Å; b = 10.814 (1) Å; c = 17.961 (4) Å; V = 812.5 (2) Å3; orthorhombic; P212121; Z = 4), corrugated CuI double chains are found in which each copper atom is coordinated by one additional 2-iodopyrazine ligand. In poly[CuI(μ-2-iodopyrazine-N,N‘)] (form II; a = 4.2679 (5) Å; b = 13.942 (2) Å; c = 13.017 (2) Å; b = 92.64 (1)°; V = 773.76 (2) Å3; monoclinic; P21/c; Z = 4), CuI single chains occur which are connected via μ-N,N‘ coordination by the 2-iodopyrazine ligands to layers parallel to (010). The thermal behavior of both forms was investigated using simultaneous differential thermoanalysis, thermogravimetry, and mass spectrometry as well as differential scanning calorimetry and temperature resolved X-ray powder diffraction. On heating, both forms decompose to copper(I) iodide, and the decomposition temperature of form I is significantly lower than that of form II. From all experiments, there is no indication of a phase transition of one form into the other or for the formation of a phase with lower amine content

Dimorphism of a New CuI Coordination Polymer:Synthesis, Crystal Structures and Properties of Catena[CuI(2-Iodopyrazine-N)] and Poly[CuI(μ₂-2-Iodopyrazine-N,N‘)]

Two modifications of the new copper(I) iodide coordination polymer CuI(2-iodopyrazine) were obtained by the reaction of CuI and 2-iodopyrazine in acetonitrile. During this reaction, intensely yellow crystals of form I appear first which transform within several minutes to intensely red crystals of form II which is the thermodynamically most stable form at room temperature. In catena[CuI(2-iodopyrazine-N)] (form I; a = 4.1830 (6) Å; b = 10.814 (1) Å; c = 17.961 (4) Å; V = 812.5 (2) Å3; orthorhombic; P212121; Z = 4), corrugated CuI double chains are found in which each copper atom is coordinated by one additional 2-iodopyrazine ligand. In poly[CuI(μ-2-iodopyrazine-N,N‘)] (form II; a = 4.2679 (5) Å; b = 13.942 (2) Å; c = 13.017 (2) Å; b = 92.64 (1)°; V = 773.76 (2) Å3; monoclinic; P21/c; Z = 4), CuI single chains occur which are connected via μ-N,N‘ coordination by the 2-iodopyrazine ligands to layers parallel to (010). The thermal behavior of both forms was investigated using simultaneous differential thermoanalysis, thermogravimetry, and mass spectrometry as well as differential scanning calorimetry and temperature resolved X-ray powder diffraction. On heating, both forms decompose to copper(I) iodide, and the decomposition temperature of form I is significantly lower than that of form II. From all experiments, there is no indication of a phase transition of one form into the other or for the formation of a phase with lower amine content

A New Design Strategy to Access Zwitterionic Metal–Organic Frameworks from Anionic Viologen Derivates

Two isostructural microporous zwitterionic metal–organic frameworks (ZW MOFs), {[M­(bdcbpy)­(OH₂)₄]·4H₂O}_<i>n</i> with M = Mn (<b>1</b>) and Ni (<b>2</b>), were synthesized by the rational design of the flexible anionic viologen derivate, 1,1′-bis­(3,5-dicarboxybenzyl)-4,4′-bipyridinium dibromide dihydrate solvate (H₄bdcbpyBr₂·2H₂O), and its self-assembly with metal­(II) acetates in an aqueous medium. Single-crystal structure analyses revealed that both compounds exhibit three-dimensional hydrogen-bonded supramolecular frameworks with one-dimensional channel pores. Significantly, the pore surfaces are lined with charge gradients employed by the ZW ligand bdcbpy^2– leading to the adsorption of hydrogen attributed to polarization effects. The thermostabilty and activation conditions were systematically investigated by thermogravimetric analysis, differential scanning calorimetry, and powder X-ray diffraction experiments. Furthermore, repeating cycles of reversible color changes are observed in air upon irradiation with UV light attributed to the formation of viologen radicals via an intermolecular electron transfer. This work also contains an in-depth literature analysis on ZW MOFs, which shows the need for the development of alternative routes for the rational design of new porous ZW MOFs

The Importance of Polymorphism in Metal–Organic Framework Studies

Polymorphic phase transitions remain frequently undetected in routine metal–organic framework (MOF) studies; however, their discovery is of major importance in interpreting structure–property relationships. We herein report a reversible enantiotropic single-crystal to single-crystal polymorphic phase transition of a new microporous MOF [Eu­(BDC)­(NO₃)­(DMF)₂]_<i>n</i> (H₂BDC = 1,4-benzenedicarboxylic acid; DMF = dimethylformamide). While modification <b>1LT</b> at 170 K crystallizes in the monoclinic space group <i>P</i>2₁/<i>c</i> with unit cell dimensions of <i>a</i> = 17.673(2) Å, <i>b</i> = 20.023(2) Å, <i>c</i> = 10.555(9) Å, β = 90.129(4)°, modification <b>1HT</b> at 290 K crystallizes in higher symmetry space group <i>C</i>2/<i>c</i> with unit cell dimensions of <i>a</i> = 17.200(7) Å, <i>b</i> = 10.737(4) Å, <i>c</i> = 10.684(4) Å, β = 90.136(2)°. This temperature-induced phase transition is accompanied by a small change in the solvent-accessible voids from 46.8 in <b>1LT</b> to 49.8% in <b>1HT</b>, which triggers a significant change in the adsorption properties as compared to a reported isostructural compound. Detailed investigations on the phase transition were studied with variable-temperature single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction, and differential scanning calorimetry measurements. The herein-presented investigations emphasize the importance of polymorphic phase transitions in routine MOF studies originating from low-temperature SCXRD data and high-temperature physical property characterizations in avoiding the use of a wrong structure in interpreting structure–property relationships

The Importance of Polymorphism in Metal–Organic Framework Studies

Polymorphic phase transitions remain frequently undetected in routine metal–organic framework (MOF) studies; however, their discovery is of major importance in interpreting structure–property relationships. We herein report a reversible enantiotropic single-crystal to single-crystal polymorphic phase transition of a new microporous MOF [Eu­(BDC)­(NO₃)­(DMF)₂]_<i>n</i> (H₂BDC = 1,4-benzenedicarboxylic acid; DMF = dimethylformamide). While modification <b>1LT</b> at 170 K crystallizes in the monoclinic space group <i>P</i>2₁/<i>c</i> with unit cell dimensions of <i>a</i> = 17.673(2) Å, <i>b</i> = 20.023(2) Å, <i>c</i> = 10.555(9) Å, β = 90.129(4)°, modification <b>1HT</b> at 290 K crystallizes in higher symmetry space group <i>C</i>2/<i>c</i> with unit cell dimensions of <i>a</i> = 17.200(7) Å, <i>b</i> = 10.737(4) Å, <i>c</i> = 10.684(4) Å, β = 90.136(2)°. This temperature-induced phase transition is accompanied by a small change in the solvent-accessible voids from 46.8 in <b>1LT</b> to 49.8% in <b>1HT</b>, which triggers a significant change in the adsorption properties as compared to a reported isostructural compound. Detailed investigations on the phase transition were studied with variable-temperature single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction, and differential scanning calorimetry measurements. The herein-presented investigations emphasize the importance of polymorphic phase transitions in routine MOF studies originating from low-temperature SCXRD data and high-temperature physical property characterizations in avoiding the use of a wrong structure in interpreting structure–property relationships

A New Design Strategy to Access Zwitterionic Metal–Organic Frameworks from Anionic Viologen Derivates

Two isostructural microporous zwitterionic metal–organic frameworks (ZW MOFs), {[M­(bdcbpy)­(OH₂)₄]·4H₂O}_<i>n</i> with M = Mn (<b>1</b>) and Ni (<b>2</b>), were synthesized by the rational design of the flexible anionic viologen derivate, 1,1′-bis­(3,5-dicarboxybenzyl)-4,4′-bipyridinium dibromide dihydrate solvate (H₄bdcbpyBr₂·2H₂O), and its self-assembly with metal­(II) acetates in an aqueous medium. Single-crystal structure analyses revealed that both compounds exhibit three-dimensional hydrogen-bonded supramolecular frameworks with one-dimensional channel pores. Significantly, the pore surfaces are lined with charge gradients employed by the ZW ligand bdcbpy^2– leading to the adsorption of hydrogen attributed to polarization effects. The thermostabilty and activation conditions were systematically investigated by thermogravimetric analysis, differential scanning calorimetry, and powder X-ray diffraction experiments. Furthermore, repeating cycles of reversible color changes are observed in air upon irradiation with UV light attributed to the formation of viologen radicals via an intermolecular electron transfer. This work also contains an in-depth literature analysis on ZW MOFs, which shows the need for the development of alternative routes for the rational design of new porous ZW MOFs

A New Design Strategy to Access Zwitterionic Metal–Organic Frameworks from Anionic Viologen Derivates

Two isostructural microporous zwitterionic metal–organic frameworks (ZW MOFs), {[M­(bdcbpy)­(OH₂)₄]·4H₂O}_<i>n</i> with M = Mn (<b>1</b>) and Ni (<b>2</b>), were synthesized by the rational design of the flexible anionic viologen derivate, 1,1′-bis­(3,5-dicarboxybenzyl)-4,4′-bipyridinium dibromide dihydrate solvate (H₄bdcbpyBr₂·2H₂O), and its self-assembly with metal­(II) acetates in an aqueous medium. Single-crystal structure analyses revealed that both compounds exhibit three-dimensional hydrogen-bonded supramolecular frameworks with one-dimensional channel pores. Significantly, the pore surfaces are lined with charge gradients employed by the ZW ligand bdcbpy^2– leading to the adsorption of hydrogen attributed to polarization effects. The thermostabilty and activation conditions were systematically investigated by thermogravimetric analysis, differential scanning calorimetry, and powder X-ray diffraction experiments. Furthermore, repeating cycles of reversible color changes are observed in air upon irradiation with UV light attributed to the formation of viologen radicals via an intermolecular electron transfer. This work also contains an in-depth literature analysis on ZW MOFs, which shows the need for the development of alternative routes for the rational design of new porous ZW MOFs

A series of three dimensional lanthanoid(III)-metal-organic frameworks with zwitterionic linker

A series of isostructural 3D lanthanoid coordination polymers, {[Ln(µ4-cbpy)2]Br·xsolvent}n (Ln = La(1), Pr(2), Nd(3), Sm(4), Gd(5), Tb(6), Dy(7) and Ho(8), (H2cbpy)Br = 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide), have been solvothermally synthesized and characterized by single-crystal X-ray diffraction, IR and elemental analysis. Powder X-ray diffraction (PXRD) and thermal analyses (TG, DTA and DTA) of 1–8 were also investigated. The single crystal X-ray diffraction analyses revealed that 1–8 were isostructural and crystallized in the monoclinic space group C2/c. In the complexes, each cbpy– acts as a tetrakis(monodentate) to connect to four Ln(III) ions. A pair of Ln(III) ions are coordinated by four carboxylate oxygen atoms to form paddle-wheel {Ln2(RCOO)4} secondary building units which are connected by four cbpy– ligand to form a 3D structure with scu topology.</p