Field-Induced Single-Ion Magnet Behavior in Nickel(II) Complexes with Functionalized 2,2':6'-2″-Terpyridine Derivatives: Preparation and Magneto-Structural Study

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)₂](ClO₄)₂∙4H₂O (1) and [Ni(terpyepy)₂](ClO₄)₂ MeOH (2) [terpyCOOH = 4'-carboxyl-2,2':6',2″-terpyridine and terpyepy = 4'-[(2-pyridin-4-yl)ethynyl]-2,2':6',2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel-nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9-200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χ_MT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to -6.0 (1) and -4.7 cm^-1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0-5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

Hydrogen-Bonded Cobalt(II)-Organic Framework: Normal and Reverse Spin-Crossover Behaviours

A novel hydrogen-bonded metal-organic framework (H-MOF) [Co(HL)2](DMF)1.2(H2O)2.4 (1·solv), in which L = 2,2’:6’,2”-terpyridine-5,5’-diyl biscarboxylate, was prepared. An intermolecular single H-bond between carboxy and carboxylate sites was present in this compound....

Visible-Light-Promoted C2 Selective Arylation of Quinoline and Pyridine N-Oxides with Diaryliodonium Tetrafluoroborate

A protocol of visible-light-promoted C2 selective arylation of quinoline and pyridine N-oxides, with diaryliodonium tetrafluoroborate as an arylation reagent, using eosin Y as a photocatalyst for the construction of N-heterobiaryls was presented. This methodology provided an efficient way for the synthesis of 2-aryl-substituted quinoline and pyridine N-oxides. This strategy has the following advantages: specific regioselectivity, simple operation, good functional group tolerance, and high to moderate yields under mild conditions.

Nitroxide–nitroxide and nitroxide–metal distance measurements in transition metal complexes with two or three paramagnetic centres give access to thermodynamic and kinetic stabilities

Broadband and highly resolved EPR distance measurements reveal multimers and their kinetic stabilities.

Unsymmetrically functionalized 5,5″-diaryl- and 5,6,5″-triaryl-2,2′:6′,2″-terpyridines: an efficient synthetic route and photophysical properties

An efficient approach for the synthesis of 5,5″- or 5,6,5″-aryl substituted 2,2′:6′,2″-terpyridines, bearing an anneleted cyclopentene unit in one of the side-chain pyridine rings for the improved solubility in organic solvents, via their 1,2,4-triazine analogues has been developed. By using this approach, various aromatic substituents were introduced in the 2,2′:6′,2″-terpyridine core. Depending on the nature of the aromatic substituents, the obtained terpyridines exhibited an intense emission in a range of ca. 344–394 nm in acetonitrile solutions. For the most representative compounds, pronounced bathochromic shifts in both absorption and emission spectra were observed compared with previously reported substituted terpyridines.

Mn (II) Complexes Based on Oligopyridines: Structure, Thermal Studies and Optical Band-Gap Determination

Two cationic complexes [Mn(II)(terpy)2]·2(PCP) and [Mn(II)(dipy)3]·2(PCP) (terpy = 2,2′:6′,2″-terpyridine) (dipy = 2,2-dipyridyl) (PCP = pentacyanopropenide) have been synthesised. Single crystal X-ray diffraction revealed that the PCP ligand acts as a counter ion. The thermal stability of these compounds was investigated. Optical absorption measurements show that the fundamental absorption edge obeys Tauc's relation for the allowed non-direct transition. The optical band gap (Eg) values equal ~2.7 eV for both complexes.

Conformations of large macrocycles and ring-in-ring complexes

A kinetically directed, stepwise approach towards molecular Borromean links enabled the isolation and structural characterization of synthetic intermediates along the way.

Towards the molecular Borromean link with three unequal rings: double-threaded ruthenium(ii) ring-in-ring complexes

Synthesis of double-threaded ruthenium(ii) ring-in-ring complexes and the Borromean link with three unequal rings detected by mass spectrometry.

Three steps in one pot: synthesis of linear bilateral extended 2,2':6',2″-terpyridineruthenium(II) complexes

Metal complexes of linear bilateral extended 2,2':6',2″-terpyridine [2,6-bis(2-substituted furo[2,3-c]pyridin-5-yl)pyridine] are topological tridentate analogues of 5,5'-functionalized 2,2'-bipyridine. The present methodology provides access to linear bilateral extended 2,2':6',2″-terpyridineruthenium(II) complexes starting from 5,5″-bis(methoxymethoxy)-4,4″-bis(substituted ethynyl)-2,2':6',2″-terpyridines via one-pot cleavage of the methoxymethyl (MOM) protecting group, cycloisomerization, and metal complexation in the presence of Ru(DMSO)4Cl2. In this reaction, ruthenium(II) likely plays a triple role, acting as a Lewis acid to cleave the MOM ether, a catalyst facilitating 5-endo-dig cyclization, and a coordination metal center, being an integral part of the final product.