Biphenyl bridged hexadentate N6-ligands – a rigid ligand backbone for Fe(ii) spin crossover complexes

Abstract

The novel hexadentate nitrogen based ligand N,N'-bis-(2-(1H-pyrazol-1-yl)pyridine-6-ylmethyl)-2,2'-biphenylenediamine (3) was synthesized and used for the preparation of iron Spin Crossover (SCO) complexes [Fe(3)][BF4]2 (4) and [Fe(3)][ClO4]2 (5), which differ only by the respective counter ion. These complex salts show different spin transition temperatures T(1/2) (135 and 157 K, respectively). This effect was studied by the investigation of the solid state structure of different low- and high-spin isomers. All complexes of this series show closely related crystal packing regardless of the counter ion, metal (Zn/Fe) and spin state. The isomer exhibiting the lower transition temperature (4) was also investigated in respect to its photomagnetic behaviour. The LIESST process could be monitored for this complex, but no reverse-LIESST was observed. The relaxation of the photo-induced state occurs at ca. 80 K, showing a complex, three-state relaxation mechanism.

Synthesis, characterization, and cytotoxic properties of mono- and di-nuclear cobalt(ii)-polypyridyl complexes

“…The mono-and di-nuclear cobalt(II) complexes, 1-3 were synthesised as outlined in Scheme 1 and 2. The pyrazole-based ligand, L 1 was prepared by refluxing ortho-phenylene diamine with two equivalences of 2-(1H-pyrazol-1-yl)-pyridine-6carbaldehyde 35 in dry methanol for 3 h under nitrogen. The ligand was isolated, after evaporation of the solvent, as colourless crystals in a reasonable yield (66%) and fully characterized by 1 H and 13 C NMR, infrared spectroscopy, and ESI-MS mass spectrometry (see Supporting Information).…”

Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

“…The most prominent example is SCO between the low-spin (LS; 1 A 1g /t 2g 6 , S = 0) and highspin (HS; 5 T 2g /t 2g 4 e g 2 , S = 2) states in iron(II) complexes (d 6 ) in the bulk material [3,4], where the discontinuous change of magnetic properties is accompanied by dramatic changes in visiblelight response that can be selectively driven by visible light or effected by temperature gradients.…”

Modification of a Hexadentate Amine based Ligand System by N‐Methylation and Effects on Spin State and Redox ­Behavior of the Corresponding Transition Metal Complexes

“…The M –N bond lengths account to 2.1–2.35 Å, showing the high‐spin state in 5 and 6 . Also the bond angles are very similar, which clarifies once more, that Co II and Zn II complexes are useful structural analogues, if the structure of a desired Fe II high‐spin complex is not available 47. Furthermore, the high stability of the high‐spin configuration can be seen from the torsion angles ( α and β ) of the biphenyl backbone and the distance of the amino nitrogen atoms (N1 ··· N4), compared with the low‐spin complex 3a ,38 for example.…”