C-Term magnetic circular dichroism (MCD) spectroscopy in paramagnetic transition metal and f-element organometallic chemistry

Abstract

This perspective provides an introduction to magnetic circular dichroism (MCD) spectroscopy and its efficacy in elucidating both fundamental electronic structure and in situ reaction speciation in d- and f-block organometallics.

ABCs of Faraday Rotation in Organic Materials

“…All reported Verdet constants were normalized by concentration (which were not reported), and so the terbium­(III) complexes in PMMA cannot be evaluated as a Faraday rotator using published data. Despite this, lanthanide complexes are a compelling candidate class of materials due to the high orbital and spin degeneracy of their incompletely filled 4f orbitals and remain a major topic of interest in the context of MCD spectroscopy …”

“…Since MCB and MCD are manifestations of the same underlying mechanisms, the large body of work studying solution-state MCD spectra of organic molecules is directly applicable to the discovery of organic thin films with large Verdet constants. Numerous reviews exist for several classes of molecular chromophores, including porphyrins and phthalocyanines, 48 paramagnetic species, 49 metalloproteins, 50 and many others. 51 However, MCD spectroscopy is usually performed in the solution state with the purpose of understanding electronic state structures and not with the objective of maximizing the magneto-optical activity in the solid state.…”

“…Despite this, lanthanide complexes are a compelling candidate class of materials due to the high orbital and spin degeneracy of their incompletely filled 4f orbitals and remain a major topic of interest in the context of MCD spectroscopy. 49 Examples of the Faraday C term are dominated by coordination complexes of paramagnetic metal atoms and organic ligands, mostly due to the higher stability and symmetry generally enjoyed by these open-shell species versus their purely organic counterparts. However, the Faraday C term has been observed in the MCD spectra of all-organic radicals.…”

Dual-signalled magneto-optical barcodes with lanthanide-based molecular cluster-aggregates

“…With this in mind, we seek to explore a new concept in security materials by creating magneto-optical barcodes accessed through magnetic circular dichroism (MCD) spectroscopy. [19][20][21][22][23] In order to demonstrate for the first time the use of MCD as a readout platform for magneto-optical barcodes, we synthesized a hexanuclear molecular cluster-aggregate (MCA), [Ln 6 (teaH) 6 (NO 3 ) 6 ], {Ln 6 }, where teaH 2− = doubly deprotonated triethanolamine as barcode material. 24,25 We opted to use MCAs because of the unique features offered by this class of compounds.…”

“…2 and Table S1 †). 33 It should be noted that at this temperature range, MCD signals are temperature insensitive, 23 representing another advantage when compared with luminescent barcodes, which could require an extra calibration step due to the strong temperature dependence of luminescence signals close to room temperature. [34][35][36][37][38] Also, despite being usually weak at this temperature range, the use of MCAs with a large number of metal sites allowed us to observe strong signals at 25 °C and with a diluted aqueous solution (0.1 mg mL −1 ).…”