Electronic Configurations and the Effect of Peripheral Substituents of (Nitrosyl)iron Corroles.

There have been debates on the electronic configurations of (nitrosyl)iron corroles for decades. In this work, pentacoordinate [Fe(TPC)(NO)], [Fe(TTC)(NO)], and [Fe(TpFC)(NO)] with different para-substituted phenyl groups (TPC, TTC, and TpFC = tris(phenyl, 4-tolyl, or 4-fluorophenyl)corrole, respectively) have been isolated and investigated by various techniques including single-crystal X-ray diffraction, UV-vis spectroscopy, cyclic voltammetry, Fourier transform infrared, NMR, and absorption fine structure spectroscopy. Multitemperature and high-magnetic-field (3, 6, and 9 T) Mössbauer spectroscopy was also applied on all three complexes, which determined the S = 0 diamagnetic states, consistent with the magnetic susceptibility and electron paramagnetic resonance measurements. Density functional theory predictions by different functionals were compared, and the new calculation strategy, which gave remarkable agreement of the experimental Mössbauer parameters (ΔEQ and δ), allowed further assignment on the electronic configuration of {FeNO}6-(corrole3-) with antiferromagnetically coupled (S = 1/2, FeIII) and (S = 1/2, NO). Correlated sequences between the electronic donating/withdrawing capability of para substituents and the reduction/oxidation potentials, metal out-of-plane displacements (Δ4 and Δ23), and Mössbauer parameters (Vzz and ΔEQ) were also established, which suggests the strong effects of peripheral substituents.

Nuclear quadrupole double resonance spectrometer with magnetic property measurement system direct current superconducting quantum interference device detector and automatic tuning.

A new nuclear quadrupole double resonance spectrometer based on a commercial superconducting quantum interference device (SQUID) setup (a Magnetic Property Measurement System (MPMS) from Quantum Design) is described. The experiment involves the indirect detection of pure quadrupole resonances (PQR) of a dilute spin system via the direct SQUID detected NMR of an abundant spin system. The experiment is conducted at low (3-20 K) temperatures and the magnetic field is cycled between a high (5.5 T) polarizing field, to an intermediate (0.1 T) detection field, to zero field where the sample is irradiated with a modulated search RF and back to the detection field. Loss of the NMR signal indicates the detection of a PQR. The RF circuit used for both the NMR and zero field irradiation is digitally controlled. Use of the External Device Control allows for the complete automation of the system. Test measurements on diphenyl ether are in good agreement with previously reported results. Pure (17)O quadrupole resonances were detected for spin systems with concentrations as low as 120 µM.