Monitoring fragmentation and oligomerization of a di-µ-methoxo bridged copper(ii) complex: structure, mass spectrometry, magnetism and DFT studies.

Analyses of the structural information of molecular fragments from the mass spectra of the solid-state products and their reaction solutions allow for the understanding of their formation and of their diverse properties. The reaction of CuCl2 and (1-methyl-1H-benzo[d]imidazole-2-yl)methanol (HL) led only to crystals containing molecular dimers of [Cu2(L)2Cl2] (Cu2). The CuII-CuII distance and Cu-OR-Cu angle in the structure are 3.044 Å and 104.8°, respectively. The magnetic susceptibility (3-400 K) is characterized by a very strong intradimer antiferromagnetic interaction of J = -465 and interdimer zj = -0.83 cm-1. But mass spectrometry of a dissolved single crystal in different source energies identifies both its fragmentation and oligomerization to [Cu] and [Cu]. DFT calculations give the relative stabilization energies of the fragments observed in ESI-MS to provide a formation process.

Thermally Induced trans-to-cis Isomerization and Its Photoinduced Reversal Monitored using Absorption and Luminescence: Cooperative Effect of Metal Coordination and Steric Substituent.

For ethene derivatives with large groups the cis-isomer is often quite unstable and unavailable. Herein, we report an exception of two stable coordination complexes, (cis-L)ZnCl2 , starting from trans-1,2-bis(1-R-benzo[d]imidazol-2-yl)ethene (R=H, L1; R=CH3 , L2) ligands under solvothermal condition (T ≥140 °C). Using the intensity of the absorption and luminescence spectra as probes we proposed its progressive cis-to-trans reversal upon irradiation with UV light, which was confirmed by powder X-ray diffraction (PXRD). Similar results observed in the series of (cis-L2)MII Cl2 [M=Fe (4), Co (5), Ni (6)] demonstrate the universal strategy. The results of PXRD, NMR spectroscopy, ESI-MS and DFT calculations support the above conclusion. NMR spectroscopy indicates that irradiation of 1 converts an optimized 71 % of the cis-isomer to trans, whereas the free trans-L1 ligand transforms to only 15 % cis-isomer under similar conditions.

Ferromagnetic coupling in copper benzimidazole chloride: structural, mass spectrometry, magnetism, and DFT studies.

Herein, quasi-square planar CuII(Hmbm)Cl2 (CBC, Hmbm = (1-methyl-1H-benzo[d]imidazol-2-yl)methanol) was arranged in a pseudo orthogonal way to form Cl-bridged chains, and further ππ interactions resulted in distorted hexagonal layers. DFT calculations reveal a bond strength order of Cu-Cl > Cu-O/N ≫ CuCl. ESI-MS data reveal several small fragments from CBC, but oligomeric [Cu], [Cu], and [Cu] for non-zero in-source energies; MS data indicates the occurrence of several chemical processes, viz. splitting of the ligand, oligomerization, and redox reaction of alcohol to aldehyde and CuII to CuI. Gibbs free energies for the fragments were estimated using DFT. The magnetic susceptibility was modeled with the ferromagnetic coupling J(Cu-Cl2aCu) = +0.99(30) cm-1 and J'(ππ) = +0.35(16) cm-1 and g = 2.38(2). HF-EPR determined the anisotropic g-values, gx = 2.24, gy = 2.16, and gz = 2.09, and a hyperfine constant of Az = 450 G. DFT calculations from crystal structure data reveal a J(Cu-Cl2aCu) of +3.6 at 296 K and +4.1 cm-1 at 90 K that dominates the magnetic properties, whereas J'(ππ) = 0.04 cm-1 is negligibly small.