FeII and CoII Complexes with Click-Derived Tripodal Ligands: Influence of the Peripheral Substituents on Geometric Structures and Magnetic Properties

Synthesis and characterisation of group 8 tris(1-benzyl-1,2,3-triazol-4-yl)-p-anisolylmethane complexes

The tris(1,2,3-triazol-4-yl)methane framework offers a highly versatile architecture for ligand design, yet the coordination chemistry of this class of ligand remains largely unexplored. We report here the synthesis and characterisation of the homoleptic complexes [M(ttzm)₂](PF₆)₂ (ttzm = tris(1-benzyl-1,2,3-triazol-4-yl)-p-anisolylmethane; M = Fe (Fe), Ru (Ru), Os (Os)). Initial attempts to prepare Ru by reaction of [Ru(p-cymene)Cl₂]₂ and ttzm also led to the isolation of the heteroleptic complex [Ru(p-cymene)(ttzm)](PF₆)₂. The structures of [Ru(p-cymene)(ttzm)](PF₆)₂, [Fe(ttzm)₂]²⁺ (as its BPh₄^- salt) and Os were solved by X-ray diffraction. The homoleptic Fe(II) and Os(II) containing cations adopt distorted octahedral geometries due to the steric interactions between the ansiole and triazole rings of the ttzm ligands. The homoleptic complexes all adopt a low-spin d⁶ configuration and exhibit reversible M(II)/M(III) processes (+0.35 to +0.72 V vs. Fc/Fc⁺). These oxidation processes are cathodically shifted relative to those of related hexatriazole donor based complexes with density functional theory (DFT) calculations showing the metal d-orbitals are destabilised through a π-donor contribution from the triazole rings. The complexes all show prominent UV-visible absorption bands between 350 and 450 nm assigned to transitions of ¹MLCT character. Whilst none of the homoleptic complexes are emissive in room temperature fluid solutions, Os is emissive at 77 K in an EtOH/MeOH glass (λ_max 472 nm).

Fluorinated Click-Derived Tripodal Ligands Drive Spin Crossover in both Iron(II) and Cobalt(II) Complexes

Control of the spin state of metal complexes is important because it leads to a precise control over the physical properties and the chemical reactivity of the metal complexes. Currently,...

Spin-state control of cobalt(II) and iron(II) complexes with click-derived tripodal ligands through non-covalent and fluorine-specific interactions

The fine-tuning of intermolecular or intramolecular non-covalent interactions (NCIs) and thus the precise synthesis of metal complexes in which the spin states can be controlled by NCIs remains challenging, even though several such complexes have been intensively studied. In this regard, we present mononuclear cobalt(II) and iron(II) complexes with "click"-derived tripodal ligands that contain fluorinated benzyl substituents in the secondary coordination sphere. The complexes were co-crystallized with different solvent molecules to decipher the effect of the crystallized solvents on NCIs, and on the spin state of the metal ion. Additionally, the fluorine-specific interactions in the secondary coordination sphere were examined. We present a first structure-property correlation between the nature of interaction of the (per)fluorinated aromatic substituents on the ligand periphery, and the spin state of the metal complexes. In particular, the TF₅TA containing ligand show interesting stacking motifs depending on the used solvent, and these interactions have an influence on the spin state of the cobalt(II) complexes. Furthermore, the iron(II) complex thereof, Fe(TF₅TA)₂(BF₄)₂·2EtOH displays spin crossover (SCO).

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

Reducible 3,6-bis(3,5-dimethyl-pyrazolyl)1,2,4,5-tetrazine was employed to isolate supramolecular air-stable [Co₄ ] and [Zn₄ ] squares, which were achieved via careful selection of counterions rather than the use of reducing agents. Magnetic susceptibility studies revealed a strong radical-Co^II exchange coupling (J_rad-Co /hc=-118 cm^-1 , -2J formalism) with a spin ground state of S_T =4, whereas the unreduced analogue revealed negligible coupling between the Co centers (J_Co-Co /hc=-0.64 cm^-1 ). Radical-radical coupling was also probed in the [Zn₄ ] congener, which led to J_rad-rad /hc=-15.9(5) cm^-1 . 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.

Structural snapshots in the copper(ii) induced azide–nitrile cycloaddition: effects of peripheral ligand substituents on the formation of unsupported μ1,1-azido vs. μ1,4-tetrazolato bridged complexes

Peripheral substituents on click-derived tripodal ligands dictate the reactivity of their copper(ii) azido complexes.