Structural and Magnetic Studies on Nickel(II) and Cobalt(II) Complexes with Polychlorinated Diphenyl(4-pyridyl)methyl Radical Ligands

Trapping an Ester Hydrate Intermediate in a π-Stacked Macrocycle with Multiple Hydrogen Bonds

Ester hydrates, as the intermediates of the esterification between acid and alcohol, are very short-lived and challenging to be trapped. Therefore, the crystal structures of ester hydrates have rarely been characterized. Herein, we present that the mono-deprotonated ester hydrates [CH3OSO2(OH)2]-, serving as the template for the self-assembly of a π-stacked boat-shaped macrocycle (CH3OSO2(OH)2)0.67(CH3OSO3)1.33@{[ClLCoII]6}·Cl4·13CH3OH·9H2O (1) (L = tris(2-benzimidazolylmethyl) amine), can be trapped in the host by multiple NH···O hydrogen bonds. In the solution of CoCl2, L, and H2SO4 in MeOH, HSO4- reacts with MeOH, producing [CH3OSO3]- via the ester hydrate intermediate of [CH3OSO3(OH)2]-. Both the product and the intermediate serve as the template directing the self-assembly of the π-stacked macrocycle, in which the short-lived ester hydrate is firmly trapped and stabilized, as revealed by single-crystal analysis.

Metalation of a Hierarchical Self-Assembly Consisting of π-Stacked Cubes through Single-Crystal-to-Single-Crystal Transformation

Single-crystal-to-single-crystal metalation of organic ligands represents a novel method to prepare metal-organic complexes, but remains challenging. Herein, a hierarchical self-assembly {(H₁₂L₈)·([N(C₂H₅)₄]⁺)₃·(ClO₄^-)₁₅·(H₂O)₃₂} (1) (L = tris(2-benzimidazolylmethyl) amine) consisting of π-stacked cubes which are assembled from eight partially protonated L ligands is obtained. By soaking the crystals of compound 1 in the aqueous solution of Co(SCN)₂, the ligands coordinate with Co²⁺ ions stoichiometrically and ClO₄^- exchange with SCN^- via single-crystal-to-single-crystal transformation, leading to {([CoSCNL]⁺)₈·([NC₈H₂₀]⁺)₃·(SCN)₁₁·(H₂O)₁₃} (2).

Understanding the Exchange Interaction between Paramagnetic Metal Ions and Radical Ligands: DFT and Ab Initio Study on Semiquinonato Cu(II) Complexes

The exchange coupling, represented by the J parameter, is of tremendous importance in understanding the reactivity and magnetic behavior of open-shell molecular systems. In the past, it was the subject of theoretical investigations, but these studies are mostly limited to the interaction between metallic centers. The exchange coupling between paramagnetic metal ions and radical ligands has hitherto received scant attention in theoretical studies, and thus the understanding of the factors governing this interaction is lacking. In this paper, we use DFT, CASSCF, CASSCF/NEVPT2, and DDCI3 methods to provide insight into exchange interaction in semiquinonato copper(II) complexes. Our primary objective is to identify structural features that affect this magnetic interaction. We demonstrate that the magnetic character of Cu(II)-semiquinone complexes are mainly determined by the relative position of the semiquinone ligand to the Cu(II) ion. The results can support the experimental interpretation of magnetic data for similar systems and can be used for the in-silico design of magnetic complexes with radical ligands.

Iridium(III) Complex Radical and Corresponding Ligand Radical Functionalized by a Tris(2,4,6-trichlorophenyl)methyl Unit: Synthesis, Structure, and Photophysical Properties

Organic radical luminescent materials with doublet excited state character based on tris(2,4,6-trichlorophenyl)methyl (TTM) have attracted extensive attention in recent years. However, how they affect the phosphorescent iridium(III) complex characterized by the triplet excited state has not been studied yet. Herein, a new iridium(III) complex radical (Ir-TTM) and corresponding ligand radical (ppy-TTM) with a TTM unit have been designed and synthesized, and their radical properties were confirmed by the single crystal structure and EPR spectra. Notably, the ligand radical ppy-TTM shows an efficient red light emission, whereas the iridium complex radical Ir-TTM emits no light, which resulted from the intramolecular quenching effect of the TTM radical unit on the iridium luminescence center. DFT calculations demonstrate that the lowest doublet (D₁) excited state of ppy-TTM shows an intramolecular charge transfer character from the 2-phenylpyridine moieties to the TTM unit, whereas the D₁ of Ir-TTM exhibits a significant charge transfer character from the iridium luminescence center moieties to the TTM unit, which further explains the luminescence quenching mechanism of the phosphorescent iridium complex radical.

Synthesis, crystal structure and magnetic properties of mer-tricyanidoiron(III) precursor-based 1D heterobimetallic complexes

Three new cyanide-bridged heterometallic complexes {{[Cu(S,S-Chxn)2][Fe(bbp)(CN)3]}2·2 H2O} n (1), {{[Cu(R,R-Chxn)2][Fe(bbp)(CN)3]}2·2 H2O} n (2) and {{[Cu(Cycam)][Fe(bbp)(CN)3]}·CH3OH·2 H2O} n (3) (bbp = bis(2-benzimidazolyl)pyridine dianion, Chxn = 1,2-diaminocyclo hexane, cyclam = 1,4,8,11-tetraazacyclodecane) have been assembled from the rarely used mer-tricyanidoiron(III) building block [PPh4]2[Fe(bbp)(CN)3] and three copper(II) compounds. The complexes have been characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. For the chiral enantiomers 1 and 2, the circular dichroism (CD) spectrum was also investigated. X-ray structural analyses revealed that the structures of the cyanide-bridged Fe-Cu complexes 1 and 2 are characterized by two crystallographically independent but structurally very similar homochiral neutral chains, each consisting of the repeating units {[Cu(S,S-Chxn)2][Fe(bbp)(CN)3]} (1) or {[Cu(R,R-Chxn)2][Fe(bbp)(CN)3]} (2). The crystal structure of 3 likewise is build up of chains consisting of {[Cu(Cyclam)][Fe(bbp)(CN)3]} building blocks. The temperature-dependent magnetic susceptibility and field dependent magnetization of the complexes showed antiferromagnetic interactions in complex 1 between the Fe(III) and Cu(II) ions, while complex 3 is ferromagnetic, indicating that the magnetic coupling through cyanide linkage is very sensitive to the structure parameters around the paramagnetic metal ions. These results have been further confirmed by fitting of the experimental data using a uniform chain model, leading to the coupling constants J = −6.35 cm−1, g = 2.08, R = 4.42 × 10−4 and J = 1.24 cm−1, g = 2.09, R = ∑(χ obsd T − χ cald T)2/∑(χ obsd T)2 = 4.67 × 10−4 for complexes 1 and 3, respectively.