Multifrequency cw-EPR and DFT Studies of an Apparent Compressed Octahedral Cu(II) Complex

Abstract

The syntheses and single-crystal X-ray structures of the mononuclear complexes [Cu(bmet)](ClO4)2·H2O, [Cu(bmet)]Br2·2MeCN, and [Zn(bmet)](ClO4)2·H2O (bmet = N,N'-bis(2,2'-bipyridin-6-ylmethyl)ethane-1,2-diamine) are described. All three complexes feature a central metal ion bound to all six N atoms of the bmet ligand, which displays a meridional-facial-facial-meridional (mffm) configuration. The three complexes show one N-M-N axis to be significantly shorter than the others in agreement with an apparent compressed octahedral geometry. The X-ray structures of a single crystal of [Cu(bmet)](ClO4)2·0.375H2O resolved from data recorded at different temperatures display no remarkable structural modifications. However, they all display both as a powder and, in solution, an axial g1 > g2 ≳ g3 > g(e) electron paramagnetic resonance (EPR) pattern at low temperature, which is indicative of tetragonally elongated octahedra, while at room temperature the Q-band EPR spectra display a more rhombic g1 ≳ g2 > g3 > g(e) pattern. The fully density functional theory optimized structure of the Cu(II) complexes displays significant structural modifications only along one N(imine)-M-N(amine) axis resulting in an elongated octahedral structure. Furthermore, the EPR parameters predicted from this structure are comparable to those determined experimentally from the axial EPR signal recorded at low temperature, consistent with the unpaired electron residing mainly in the {3d(x(2)-y(2))} orbital. The structural and electronic properties of [Cu(bmet)](2+) are different from those in other previously described dynamic Jahn-Teller systems. We propose that these data can be rationalized by a dynamic Jahn-Teller effect perturbed by the strain of the hexadentate bmet ligand.

Synthesis and structural and DNA binding studies of mono‐ and dinuclear copper(II) complexes constructed with ─O and ─N donor ligands: Potential anti‐skin cancer drugs

“…The X‐band EPR spectra of polycrystalline powders of compounds 1 – 4 were recorded at room temperature (298 K) (Figure S2). The values of EPR parameter g are consistent with a distorted octahedral arrangement (CuN 2 O 4 ) for compound 1 and distorted square pyramidal arrangement (CuN 2 O 2 O′) for compounds 2 – 4 which indicate the ground state of Cu(II) ion as listed in Table …”

Synthesis, crystal structure and biological properties of a cis-dichloridobis(diimine)copper(II) complex

“…The mean Cu-N bond length is 2.116 Å , which is similar to that of reported copper(II) complexes (Bhat et al, 2011(Bhat et al, , 2017. Four long bonds [Cu-N2 = Cu-N2 i = 2.189 (3) Å and Cu-Cl1 = Cu-Cl1 i = 2.5579 (14) Å ; symmetry code: (i) Àx + 1, y, Àz + 3 2 ] are in a plane and two short bonds [Cu-N1 = Cu-N1 i = 2.043 (2) Å ] are trans to each other, suggesting a compressed octahedral geometry; similar compressed octahedral geometries have been observed for some octahedral copper complexes (Hall et al, 2016;Solanki et al, 1998;Biswas et al, 2008). The heterocyclic ligands in the title complex are oriented perpendicular to each other, which may be due to the steric clash of H atoms of the organic rings, which is similar to the situation seen in a five-coordinated [CuCl(1,10-phenantroline) 2 ]Cl complex (Onawumi et al, 2010).…”

Synthesis of Fullerotetrahydroquinolines via [4 + 2] Cycloaddition Reaction of [60]Fullerene with in Situ Generated Aza-o-quinone Methides

“…Furthermore, after the reaction was completed, we observed a green copper precipitate, which was the same as that formed from the control reaction of 1a with Cu 2 O and 1,10-phen at 120 °C for 3.0 h in CB. The electron paramagnetic resonance (EPR) experiment of the green solid in DMSO suggested that a Cu­(II) species existed . The X-ray diffraction experiment further confirmed that the single crystal 4 grown from the green copper solid was a complex of 1,10-phen and CuCl 2 (see the Supporting Information).…”