Synthesis and properties of N-methylimidazole solvates of vanadium(ii), chromium(ii) and iron(ii) phthalocyanines. Strong NIR absorption in VII(MeIm)2(Pc2?)?

Dalton Transactions Pub Date: 2018-02-21 DOI: 10.1039/C8DT00459E

Abstract

N-Methylimidazole (MeIm) solvates of vanadium(II), chromium(II) and iron(II) phthalocyanines: [VII(MeIm)2(Pc2?)]0·MeIm (1) and [MII(MeIm)2(Pc2?)]0·2C6H4Cl2 (M = V (2), Cr (3), and Fe (4)) have been obtained and studied in a crystalline form. It has been shown that central metal atoms have the +2 oxidation state in 1–4 and dianionic Pc2? macrocycles are formed. Optical spectra of 1–3 (VII, CrII) are different from that of 4 (FeII) due to the appearance of intense absorption bands in the NIR range at 1187 nm for 1 and 2 and 1178 nm for 3 and manifestation of multiple bands in the visible range. Absorption in the NIR range is explained by unusually small gaps between the molecular orbitals at around HOMO and LUMO for MeIm solvated CrIIPc and VIIPc. The essential diradicaloid character of the Pc macrocycles in [CrII(MeIm)2(Pc2?)]0, in which α- and β-orbitals are distributed in different regions of the macrocycle, has also been shown. In this case, the diradicaloid character is comparable to that of aromatic hydrocarbon heptacene. Magnetic properties of 1–3 are defined by metal atoms with a S = 3/2 spin state for VII and S = 1 for CrII. Compounds 1–3 manifest broad isotropic EPR signals at 4.2 K with g = 2.0188 and a linewidth (ΔH) of 81.8 mT for 1 (VII), g = 1.8300 and a linewidth ΔH = 161.0 mT for 2 (VII), and g = 2.0534 and ΔH = 60.27 mT for 3 (CrII). These signals shifted to smaller g-factors with the temperature increase. Integral intensity of narrow EPR signals from Pc˙3? does not exceed 0.1% from those of broad signals in 1–3. Complex 4 is EPR silent due to the presence of diamagnetic FeII and Pc2?.

Graphical abstract: Synthesis and properties of N-methylimidazole solvates of vanadium(ii), chromium(ii) and iron(ii) phthalocyanines. Strong NIR absorption in VII(MeIm)2(Pc2?)
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