An Iron(II) Spin Crossover Complex with a Maleonitrile Schiff base‐like Ligand and Scan Rate‐dependent Hysteresis above Room Temperature

Abstract

A Schiff base-like ligand bearing a maleonitrile backbone was synthesized and converted in two steps to an octahedral iron(II) complex with axial imidazole ligands. Single crystal X-ray structure analysis of this complex revealed a 3D hydrogen bond network based on the NH groups of the axial imidazole ligands that act as donors. Interestingly, temperature-dependent magnetic measurements showed an abrupt spin crossover with hysteresis above room temperature. Thereby, the hysteresis width features a strong scan rate dependency leading to a 6 K wide hysteresis at a scan rate of 5 K/min and 1 K width when measured in settle mode. This kinetic effect is further investigated by DSC measurements verifying the strong scan rate dependency of the hysteresis width. The small hysteresis was additionally followed using temperature-dependent PXRD. For comparison, the corresponding pyridine complex was synthesized as well.

Quenched Lewis Acidity: Studies on the Medium Dependent Fluorescence of Zinc(II) Complexes

“…In the case of H 2 (1) and H 2 (2) the free Schiff base‐like ligands were obtained directly through reaction of diaminomaleonitrile with the respective keto‐enol ether in the presence of p ‐toluenesulfonic acid ( p ‐TSA); H 2 (2) has been reported previously. [11] H 2 (1) was received from MeOH as an orange solid in 44 % yield. The identity and purity of the ligands was confirmed by 1 H NMR spectroscopy, mass spectrometry, and elemental analysis.…”

“…Methoxymethylenemethylacetoacetate, ethoxymethyleneethyl‐acetoacetate, ethoxymethylene‐1,1,1‐trifluoroacetylacetone, and H 2 (2) were synthesised as described in literature. [ 11 , 24 ] Diaminomaleonitril (98 %, Sigma Aldrich), p ‐toluenesulfonic acid (98 %, Merck), and Zn(OAc) 2 ⋅ 2 H 2 O (97+%, Alfa Aesar) were used without further purification. Methanol, ethanol, THF, and pyridine were of analytical grade and used without further purification.…”

Asymmetric Design of Spin-Crossover Complexes to Increase the Volatility for Surface Deposition

“…Herein, we apply such a strategy to a homoleptic SCO complex based on the combination of an Fe II ion with tridentate Schiff-base type ligands. The ligands of Schiff-base type are well established to provide an appropriate ligand field strength for the occurrence of SCO in Fe II complexes. − We demonstrate that the complex [Fe­( t Bu 2 qsal) 2 ] (Scheme ), where t Bu 2 qsal – is a deprotonated form of 2,4-di­( tert -butyl)-6-((quinoline-8-ylimino)­methyl)­phenol ( t Bu 2 qsalH), undergoes an abrupt spin transition centered at 123 K with a 12 K thermal hysteresis. The complex also exhibits light-induced spin-state switching at low temperatures.…”

Hidden Lewis acidity: Studies on the medium and structure dependent fluorescence of zinc(II) complexes

“…In the case of H2(1) and H2(2) the free Schiff base-like ligands were obtained directly through reaction of diaminomaleonitrile with the respective keto-enol ether in the presence of p-toluenesulfonic acid (p-TSA); H2(2) has been reported previously. [11] H2(1) was received from MeOH as an orange solid in 44% yield. The identity and purity of the ligands was confirmed by 1 H NMR spectroscopy, mass spectrometry, and elemental analysis.…”

“…Methoxymethylenemethylacetoacetate, ethoxymethyleneethylaceto-acetate, ethoxymethylene-1,1,1trifluoroacetylacetone, and H2(2) were synthesised as described in literature. [11,23] -Diaminomaleonitril (98%, Sigma Aldrich), p-toluenesulfonic acid (98%, Merck), and Zn(OAc)2•2 H2O (97+%, Alfa Aesar) were used without further purification. Methanol, ethanol, THF, and pyridine were of analytical grade and used without further purification.…”