Two new trinuclear copper(II) complexes, [Cu3(μ3-OH)(daat)(Hdat)2(ClO4)2(H2O)3](ClO4)2·2H2O (1) and [Cu3(μ3-OH)(aaat)3(H2O)3](ClO4)2·3H2O (2) (daat = 3,5-diacetylamino-1,2,4-triazolate, Hdat = 3,5-diamino-1,2,4-triazole, and aaat = 3-acetylamino-5-amino-1,2,4-triazolate), have been prepared from 1,2,4-triazole derivatives and structurally characterized by X-ray crystallography. The structures of 1 and 2 consist of cationic trinuclear copper(II) complexes with a Cu3OH core held by three N,N-triazole bridges between each pair of copper(II) atoms. The copper atoms are five-coordinate with distorted square-pyramidal geometries. The magnetic properties of 1 and 2 and those of five other related 1,2,4-triazolato tricopper(II) complexes with the same triangular structure (3–7) (whose crystal structures were already reported) have been investigated in the temperature range of 1.9–300 K. The formulas of 3–7 are [Cu3(μ3-OH)(aaat)3(H2O)3](NO3)2·H2O (3), {[Cu3(μ3-OH)(aat)3(μ3-SO4)]·6H2O}n (4), and [Cu3(μ3-OH)(aat)3A(...

Antisymmetric exchange in triangular tricopper(II) complexes: correlation among structural, magnetic, and electron paramagnetic resonance parameters.

In continuation of our research interest in pyrazole-based multifunctional metal organic frameworks (MOFs), we report here three Cu(II) MOFs using pyrazole and various aromatic carboxylic acid-based ligands. The main theme of interest is to design functional MOFs by imparting a multinuclear metal center as a secondary building unit (SBU). Accordingly, three MOFs are synthesized based on a hexanuclear Cu-pyrazolate unit as the SBU with some intriguing structural networks like (4,4) type herringbone grid or an archetypal Kagome topology. We have successfully synthesized functional MOFs by incorporating hexanuclear Cu-pyrazolate SBU-specific properties viz. magnetism and catalysis, the central theme of this work. All the MOFs show some photocatalytic degradation of toxic dye molecules. On the other hand, magnetic behaviors of MOF-2 and MOF-3 associated with the Cu6 unit have also been investigated.

Designing Functional Metal–Organic Frameworks by Imparting a Hexanuclear Copper-Based Secondary Building Unit Specific Properties: Structural Correlation With Magnetic and Photocatalytic Activity

Copper threesome: A hexapyridyl ligand based upon a 1,3,5-triphenylbenzene framework coordinates three metal centers in a constrained environment (see picture). The tricopper(I) complex reduces dioxygen to form a tricopper(II) cluster. The capping anions affect the magnetism and EPR spectra of these species and reveal a linear dependence between the antiferromagnetic exchange parameter and the Cu-O-Cu angles.

Trinucleating Copper: Synthesis and Magnetostructural Characterization of Complexes Supported by a Hexapyridyl 1,3,5-Triarylbenzene Ligand†

Trinuclear first row transition metal complexes of a hexapyridyl, trialkoxy 1,3,5-triarylbenzene ligand

The ferromagnetic couplings were observed in an unpublished crystal that consists of binuclear copper(II) complexes, namely, [Cu2(μ1,3-SCN)2(PhenOH)(OCH3)2(HOCH3)2] (PhenOH = 2-hydroxy-1,10-phenanthroline), and in the binuclear complex Cu(II) ion assumes a distorted octahedral geometry and thiocyanate anion functions as a μ1,3-SCN− equatorial–axial (EA) bridging ligand. The analysis for the crystal structure indicates that there are three types of magnetic coupling pathways, in which two pathways involve π–π stacking between the adjacent complexes and the third one is the μ1,3-SCN− bridged pathway. The fitting for the data of the variable-temperature magnetic susceptibilities shows that there is a ferromagnetic coupling between adjacent Cu(II) ions with J = 50.02 cm−1. Theoretical calculations reveal that the two types of π–π stacking resulted in ferromagnetic couplings with J = 4.16 cm−1 and J = 2.75 cm−1, respectively, and the bridged thiocyanate anions pathway led to a weaker ferromagnetic interaction with J = 0.88 cm−1. The theoretical calculations also indicate that the ferromagnetic coupling sign from the two types of π–π stacking does not accord with McConnell I spin-polarization mechanism. The analysis for the Wiberg bond indexes that originate from the π–π stacking atoms indicates that the Wiberg bond indexes are relevant to the associated magnetic coupling magnitude and the Wiberg bond index is one of the key factors that dominates the associated magnetic coupling magnitude.

π–π Stacking and ferromagnetic coupling mechanism on a binuclear Cu(II) complex

The mechanisms of the magnetic coupling interactions for two trigonal-bipyramid trinuclear Cu(II) complexes Cu3(mu3-X)2(mu-pz)3X3 (X = Cl and Br, respectively) and three trigonal trinuclear Cu(II) complexes Cu3(mu3-X)(mu-pz)3Cl3 (X = Cl, Br, and O) are investigated by the calculations based on density functional theory combined with broken-symmetry approach (DFT-BS). The research on the magneto-structural correlation reveals that the magnetic coupling interaction is sensitive to the Cu-(mu3-X)-Cu angle. With the Cu-(mu3-X)-Cu angle changing from 76 to 120 degrees, the magnetic coupling interaction is switched from ferromagnetic to antiferromagnetic. According to the analysis of the molecular orbitals and the variation of the spin-state energies versus the ratio of the magnetic coupling constants, it is found that there exists spin frustration phenomenon in these complexes.

Theoretical investigation on triagonal symmetry copper trimers: magneto-structural correlation and spin frustration.

The mechanisms of magnetic exchange interactions in two heterobridged μ-hydroxyl-μ-X dicopper complexes A and B (X = azaindole for A and X = pyrazole for B) are investigated by the calculations based on density functional theory combined with the broken-symmetry approach (DFT-BS). It is found that although the coordination circumstances of the copper centers in the two complexes are very similar, the magnetic magnitudes and signs are diametrically opposed. By the theoretical analyses of magnetic orbital interaction and spin distribution, it is indicated that the difference between the magnetic properties of the two complexes is due to the distinction of orbital interaction of two bridge ligands. Namely, the weak ferromagnetic coupling for complex A arises from the orbital countercomplementarity of the hydroxo and azaindole bridges while the strong antiferromagnetic coupling for complex B arises from the orbital complementarity of the hydroxo and pyrazolato bridges.

Magnetic interactions in two heterobridged dinuclear copper(II) complexes: orbital complementarity or countercomplementarity?

Magnetic coupling interactions of a MnIII4 system are investigated by calculations based on density functional theory combined with a broken-symmetry approach (DFT-BS). Three different interactions including ferromagnetic and antiferromagnetic coupling are concomitant in this complex. This magnetic phenomenon of the complex is due to the different bridging angles between the Mn(III) centers in the three different models and the orbital complementarity of the μ-pzbg and μ-OCH3 bridging ligands, which is proven by the analyses of the molecular orbitals. According to the analyses of the magneto-structural correlation, it is revealed that the magnetic coupling interaction switches from ferromagnetic to antiferromagnetic at the point of the bridging angle Mn–(μ-OCH3)–Mn = 99°, which is equal to the value in the origin crystal. Significant correlation between the magnetic properties and the component of the d orbitals in these systems shows that the larger contribution of the dz2 orbital corresponds to the larger ferromagnetic coupling interaction. These results should provide a means to control the magnetic coupling of the polynuclear Mn systems, which is instructive for the design of new molecular magnetic materials.

You-Min Sun

Papers

Theoretical investigation on triagonal symmetry copper trimers: magneto-structural correlation and spin frustration.

Magnetic interactions in two heterobridged dinuclear copper(II) complexes: orbital complementarity or countercomplementarity?

Insights into the control of magnetic coupling in the Mn4III complex: from ferromagnetic to antiferromagnetic

DFT-BS study on the magnetic coupling interaction in a series of (R-Bpmp)MnII2(μ-OAc)2 complexes