Probing Magnetic‐Exchange Coupling in Supramolecular Squares Based on Reducible Tetrazine‐Derived Ligands

Abstract

Reducible 3,6-bis(3,5-dimethyl-pyrazolyl)1,2,4,5-tetrazine was employed to isolate supramolecular air-stable [Co ] and [Zn ] squares, which were achieved via careful selection of counterions rather than the use of reducing agents. Magnetic susceptibility studies revealed a strong radical-Co exchange coupling (J /hc=-118 cm , -2J formalism) with a spin ground state of S =4, whereas the unreduced analogue revealed negligible coupling between the Co centers (J /hc=-0.64 cm ). Radical-radical coupling was also probed in the [Zn ] congener, which led to J /hc=-15.9(5) cm . These results highlight the versatile air-stable coordination chemistry of tetrazine and the importance of exploiting easily reducible delocalized radical to promote strong exchange coupling between spin carriers.

Enhancing Magnetic Communication between Metal Centres: The Role of s‐Tetrazine Based Radicals as Ligands

“…In parallel to the aforementioned studies, our group explored the coordination chemistry of 3,6‐bis(3,5‐dimethyl‐1 H ‐pyrazol‐1‐yl)‐ s ‐tetrazine (bpytz) in order to prepare stable radical compounds under aerobic conditions. Through this approach, we were able to isolate analogous molecular Co II squares in which the bpytz adopts either the natural form ([Co 4 ( μ ‐bpytz) 4 (CH 3 CN) 6 (H 2 O) 2 ]⋅8(BF 4 )⋅(CH 3 CN); 6 ) or the anionic radical form ([Co 4 ( μ ‐bpytz .− ) 4 (PhCOO) 4 ]⋅(C 2 H 5 ) 2 O⋅(CH 3 OH)⋅ 0.5(H 2 O); 7 ) [63] . With these complexes, we could therefore carefully probe the nature and strength of the magnetic exchange between the paramagnetic centres.…”

“…In parallelt ot he aforementioned studies, our group explored the coordination chemistry of 3,6-bis(3,5-dimethyl-1Hpyrazol-1-yl)-s-tetrazine (bpytz) in order to prepare stable radical compounds under aerobic conditions. Through this approach,w ew ere able to isolate analogous molecular Co II squares in which the bpytz adopts either the natural form [63] With thesec omplexes,w ec ould therefore carefully probe the nature ands trengtho ft he magnetic exchange between the paramagnetic centres.A se vident by the cT vs. T plots in Figure 5( 300 Kt o1 .8 Ku nder 1000 Oe applied field), the magnetic behaviour of 6 and 7 differ significantly from one another.T he room temperature cT value of 10.2 cm 3 Kmol À1 for 6 is higher than the expected spin-only value of 7.5 cm 3 Kmol À1 due to unquenched first order angular momentum for highly anisotropic Co II complexes. The cT vs. T profilei ndicates antiferromagnetic exchange interactions between the high spin (HS) Co II ions, leading to as inglet ground state at low temperature.…”

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

“…[15][16][17][18][19][20][21][22] These molecules are of interesti nc oordination chemistry due to their facile functionalisationa nd their redoxa ctivity,w hich can enhancem agnetic communication between metal ions. [23][24][25][26] For these reasons, the quest for tetrazine-based compounds is an extremely activef ield of research in coordinationc hemistry.…”

A tunable lanthanide cubane platform incorporating air-stable radical ligands for enhanced magnetic communication

“…Here, we propose an avenue to reinvigorate the field of magnetic lanthanide cubane clusteraggregates, by incorporating air-stable radical ligands within their frameworks, thereby promoting non-negligible magnetic interactions. This work focuses on the non-innocent redox properties of 3,6-bis(3,5-dimethylpyrazol-1-yl)−1,2,4,5-tetrazine (BPyTz), whose coordination to first row transition metal ions has previously yielded anionic air-stable radicals (BPyTz •− ) 21,22 . The ability of this ligand to generate air-stable radicals is rather unique compared to other radical-bridged systems, such as those based on 2,2′-bipyrimidine 23 , N 2 24 , or tetrapyridophenazine 25 , all of which are highly unstable in air and require strong reducing agents during synthesis.…”