Asymmetric Ring Opening in a Tetrazine‐Based Ligand Affords a Tetranuclear Opto‐Magnetic Ytterbium Complex

Abstract

We report the formation of a tetranuclear lanthanide cluster, [Yb4(bpzch)2(fod)10] (1), which occurs from a serendipitous ring opening of the functionalised tetrazine bridging ligand, bpztz (3,6‐dipyrazin‐2‐yl‐1,2,4,5‐tetrazine) upon reacting with Yb(fod)3 (fod−=6,6,7,7,8,8,8‐heptafluoro‐2,2‐dimethyl‐3,5‐octandionate). Compound 1 was structurally elucidated via single‐crystal X‐ray crystallography and subsequently magnetically and spectroscopically characterised to analyse its magnetisation dynamics and its luminescence behaviour. Computational studies validate the observed MJ energy levels attained by spectroscopy and provides a clearer picture of the slow relaxation of the magnetisation dynamics and relaxation pathways. These studies demonstrate that 1 acts as a single‐molecule magnet (SMM) under an applied magnetic field in which the relaxation occurs via a combination of Raman, direct, and quantum tunnelling processes, a behaviour further rationalised analysing the luminescent properties. This marks the first lanthanide‐containing molecule that forms by means of an asymmetric tetrazine decomposition.

Detection of Sub‐Terahertz Raman Response and Nonlinear Optical Effects for Luminescent Yb(III) Complexes

“…Accordingly, the NIR luminescence spectra for YbS and YbSe reveal four major peaks centered around 923, 975, 1000, and 1040 nm upon UV excitation, resulting in radiative transitions from multi plets of 2 F 5/2 excited state to the multiplets of 2 F 7/2 ground state of Yb 3+ ions (Figure 5e,f). [26] It is worth emphasizing that these emissions are in agreement with the first and second biological windows (I−BW and II−BW). [23] To examine the origin of these peaks in detail, we performed the excitation spectra measurements over a wide wavelength range from 200 to 950 nm for the two selected emission peaks of 975 and 1040 nm, which are rarely reported for Yb(III) complexes (Figure S15, Supporting Information).…”

“…The χ M T value at 300 K for YbS and YbSe is found to be 2.2 and 2.3 cm 3 mol −1 K, respectively, resembling proximity with the predicted magnetic susceptibility of 2.6 cm 3 mol −1 K for free Yb(III) ions. [26] As the temperature decreases, χ M T product declines to reach 1.0 and 0.9 cm 3 mol −1 K for YbS and YbSe due to the thermal depopulation of m J sublevels close to each other. Magnetization (M) versus field (H) curves measured at reveal a constant increase until 1.65 µ B at 50 kOe.…”

“…Such an observation is reported for other Yb(III)-doped crystals in a similar energy range (Figure 5e,f). [26] The emission peak intensity declines with decreasing temperature. The broad emission peak around 923 nm can be assigned as the hot band since it disappears below 100 K, suggesting that the emission level for this peak is a higher excited multiplet, depopulating as temperature decreases (Figure 5a,b).…”

Di- and Tetranuclear Dysprosium Single-Molecule Magnets Bridged by Unprecedentedly Disassembled Nitrogen-Enriched Tetrazine Derivatives

“…30−34 At present, the coordination chemistry of tetrazine derivatives from dipyrimidine is scarcely developed, and there is only one report on asymmetric ring opening in a tetrazine-based ligand in combination with lanthanides. 35 What is more, the nitrogen-enriched bridged ligand 3,6-di(pyrimidin-2-yl)-1,2,4,5-tetrazine (bmtz) has been reported involving coordination with transition metals, 36−39 while none of the corresponding lanthanide-based complexes have been reported so far. More importantly, both N8-containing bmtz and its disassembled moiety N6-membered (Z)-N-[(E)-pyrimidin-2ylmethylene]pyrimidine-2-carbohydrazonate (bmzch), possibly transformed into radical bridges to build SMMs, are promising candidates.…”

Self-assembly of Ni(ii) metallacycles (a square and a triangle) supported by tetrazine radical bridges

“…10 Such an open-shell bridge may bring much stronger magnetic interaction through the direct overlap of orbitals that contain the unpaired electrons. For example, Dunbar 6,11 and Murugesu 12 groups prepared a series of dinuclear and tetranuclear complexes using tetrazine radical bridges, in which strong antiferromagnetic (AF) or ferromagnetic (F) interactions with coupling constants of ±100 cm −1 between the radical and the neighbouring metal ion (AF for Co II –radical and F for Ni II –radical) were observed. With the incorporation of azide ions as secondary bridges, we recently prepared a series of [2 × 2] grid-like [M II 4 ] clusters based on 3,6-substituted pyridazine derivatives within cis -bridging modes as dictated by the end-on azido bridges.…”