The first 3, 5, 6-trichloropyridine-2-oxyacetate bridged manganese coordination polymer with features of π⋯π stacking and halogen⋯halogen interactions: Synthesis, crystal analysis and magnetic properties

Solvothermal or hydrothermal methods of M(NO3)2·6H2O (M = Ni(II) or Co(II)) with an N donor (1,4-bis(imidazol-1-yl)benzene, 1,4-bib) and auxiliary deprotonated biphenyltetracarboxylates (2,2′,5,5′-biphenyltetracarboxylic acid, H4(o,m-bpta); 3,3′,5,5′-biphenyltetracarboxylic acid, H4(m,m-bpta); or 3,3′,4,4′-biphenyltetracarboxylic acid, H4(m,p-bpta)) give five novel coordination polymers in H2O–DMF or H2O, namely, [Ni2(1,4-bib)3(o,m-bpta)(H2O)2] (1), [Ni2(1,4-bib)3(HCO2)4(H2O)2]·5H2O (2), [Co2(1,4-bib)2(m,m-bpta)(H2O)4] (3), [Ni2(1,4-bib)2(m,p-bpta)(H2O)2] (4) and [Co2(1,4-bib)2(m,p-bpta)(H2O)2] (5). The structural properties of the complexes have been acquired by single-crystal XRD and further characterized by EA, IR spectroscopy, powder XRD and TG analysis. The framework of 1 is constructed of a 3D interpenetration structure with a (4·62)2(42·62·82) topology. Complex 2 exhibits a 3D supramolecular framework assembled by 1D mutual interpenetration chains. Complex 3 generates a 3D supramolecular architecture from (4,4)-connected 2D layers. Complexes 4 and 5 exhibit isomorphism, having 2D sheet structures with (4,4)-grid units. These results reveal that the 1,4-bib ligand cooperating with different biphenyltetracarboxylic acids can be used as versatile building blocks for the construction of metal–organic frameworks. Magnetic susceptibility measurements indicate the presence of weak ferromagnetic exchanges between adjacent Ni(II) ions with g = 2.235(5), 2.223(7) and J = 0.906(1), 2.220(1) cm−1 for 1 and 4, respectively.

Self-assembly and magnetic properties of Ni(II)/Co(II) coordination polymers based on 1,4-bis(imidazol-1-yl)benzene and varying biphenyltetracarboxylates

Nanojars are large (2 nm wide) anion-incarcerating coordination complexes of the composition [anion⊂{Cu(μ-OH)(μ-pz)}n] (n = 27-36), formed by the self-assembly of simple Cu(2+), HO(-), and pyrazolate (pz(-) = C3H3N2(-)) ions in the presence of certain anions with large hydration energy (e.g., CO3(2-), SO4(2-), PO4(3-), HPO4(2-)). Nanojars display spectacular chemical properties, such as unparalleled anion binding strength and, as shown herein, extraordinary resistance to extreme alkalinities (10 M NaOH). To shed light on the mechanism of the self-assembly process leading to these distinctive constructs, we employed an array of complementary techniques including mass spectrometry, pH titration, UV-vis and NMR spectroscopies, chemical synthesis, and single-crystal X-ray diffraction. In the reaction of Cu(NO3)2, pyrazole, NaOH, and Na2CO3 in tetrahydrofuran (THF), the first major intermediate is a trinuclear copper pyrazolate complex, [Cu3(μ3-OH)(μ-pz)3(NO3)2(H2O)], which was separately isolated and characterized. As the THF-insoluble NaOH slowly reacts, the nitrate ions are gradually precipitated out as NaNO3 and replaced by hydroxide ions. The resulting species, [Cu3(μ3-OH)(μ-pz)3(OH)x(NO3)3-x](-) (x = 1-3), have unstable terminal Cu-OH groups and react with each other to yield OH-bridged units, such as [Cu3(μ3-OH)(μ-pz)3(NO3)2]2(μ-OH) and then [{Cu3(μ3-OH)(μ-pz)3(μ-OH)2}x(NaNO3)y(Na2CO3)z] oligomers. The Cu3(OH)3(pz)3 repeating units of these oligomers have the same composition as the [Cu(OH)(pz)]n (n = 3x) nanojars and rearrange to the final products, Na2[CO3⊂{Cu(μ-OH)(μ-pz)}n] (n = 27, 29, 31), while eliminating the last amounts of NaNO3. pH titration, UV-vis monitoring, and chemical synthesis also confirm the formation of the trinuclear intermediate, followed by its clean transformation to nanojars. While displaying an unusual stability to high pH, nanojars are sensitive to acids stronger than water, a property exploitable for the recovery of the incarcerated anion. On lowering the pH, nanojars first break down to trinuclear complexes and finally to copper ions and pyrazole. This process is fully reversible, and nanojars are reassembled as pH is increased.

From Ordinary to Extraordinary: Insights into the Formation Mechanism and pH-Dependent Assembly/Disassembly of Nanojars.

In an unusual reaction of [Pd(L1)Cl2] (L1 = 2-(arylazo)pyridine) with amines, a new series of palladium complexes [Pd(L2•–)Cl] (L2 = 2-((2-amino)arylazo)pyridine) (1a–1h) were isolated. The complexes were formed via N–H and N–C bond cleavage reactions of 1°/2° and 3° amines, respectively, followed by regioselective aromatic ortho-C–N bond formation reaction and are associated with ortho-C–H/ortho-C–Cl bond activation. A large variety of amines including both aromatic and aliphatic were found to be effective in producing air-stable complexes. Identity of the resultant complexes was confirmed by their X-ray structure determination. Efforts were also made to understand the mechanism of the reaction. A series of experiments were performed, which point toward initial ligand reduction followed by intraligand electron transfer. Examination of the structural parameters of these complexes (1) indicates that the in situ generated ligand coordinated to the PdII center serves as the backbone of these air-stable monor...

Regioselective ortho Amination of Coordinated 2-(Arylazo)pyridine. Isolation of Monoradical Palladium Complexes of a New Series of Azo-Aromatic Pincer Ligands.

Copper(II) complex with L-arginine – Crystal structure, DFT calculations, spectroscopic, thermal and magnetic properties

The π-π stacking interaction, one of the main intermolecular forces, sometimes leads to amazing magnetic properties. Although the concept has been raised that spin density is one of the main factors that contribute to the magnetic coupling strength in intermolecular magnetic coupling systems, it has not been confirmed either experimentally or theoretically to date. Herein we present a study on the magnetostructural data of seven unpublished Cu(II) complexes and ten reported radicals. It is confirmed for the first time that the spin density on short contact atoms is a major factor that contributes to the π-π stacking magnetic coupling strength. Based on the reported data to date, when the short contact distance is larger than the default contact radius, medium or relatively strong magnetic coupling strength could be obtained only if the spin density on the short contact atoms is greater than 0.1350; when the C···C short contact is less than the default contact radius of 3.4 A, but not less than 3.351 A, and the spin density is less than 0.1, neither medium nor strong magnetic coupling strength could be observed. Further, when the short contact distance decreases with a temperature drop, the spin densities on the relevant short contact atoms increase. In the complexes reported the small spin densities on the relevant short contact atoms are the major factors that result in the weak π-π magnetic coupling strength.

π–π Stacking, spin density and magnetic coupling strength

Anti-ferromagnetic interaction was observed in a new crystal that consists of mononuclear CoII complexes, namely [Co(PMP)(N3)] (PMP = 2,9-bis(pyridin-2-methoxyl)-1,10-phenanthroline); in the mononuclear complex CoII has a distorted trigonal-bipyramidal geometry. Analysis for the crystal structure indicates six magnetic coupling pathways among adjacent complexes, in which three involve π–π stacking and the other three deal with intermolecular interactions. The fitting for the variable-temperature magnetic susceptibilities with the Curie–Weiss formula shows an anti-ferromagnetic interaction between adjacent CoII ions with θ = −5.49 K = −3.82 cm−1. Theoretical calculations on the spin section reveal that the three π–π stacking systems result in magnetic coupling constants 2J = −0.10 cm−1, −0.10 cm−1, and 1.24 cm−1, respectively, and the three intermolecular interactions lead to weak anti-ferromagnetic interactions with 2J = −0.36 cm−1, −0.26 cm−1, and −0.32 cm−1, respectively. The theoretical calculations an...

Intermolecular interaction and magnetic coupling mechanism on a mononuclear CoII complex

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π–π Stacking, spin density and magnetic coupling strength

Intermolecular interaction and magnetic coupling mechanism on a mononuclear CoII complex