Cooperative spin transition in a lipid layer like system

Abstract

A novel iron(II) mononuclear spin transition complex [FeL(py)(2)] displays an abrupt spin transition around 225 K accompanied by a very wide thermal hysteresis loop (∼50 K) that spreads out over 100 K. Crystal structure analysis in both low-spin and high-spin states reveals a lipid layer-like arrangement of the complex molecules and provides insights into the spin switching mechanism.

Influence of the Alkyl Chain Length on the Self‐Assembly of Amphiphilic Iron Complexes: An Analysis of X‐ray Structures

“…The structure of an octahedral spin crossover complex with two alkyl chains of 16 carbon atoms was published recently in the HS and the LS state ( 12 LS and 12 HS ) 17. As for the complexes with C12 alkyl chains, a lipid‐layer‐like structure is observed in the crystal packing.…”

“…For complexes with C16 alkyl chains the situation is very similar. Unfortunately, only the crystal structure of one complex 12 (HS and LS) could be obtained so far 17. The axial pyridine ligands fit exactly in combination with substituent a and the C16 alkyl chains (( H + B )/ L for the complex in HS: 1.00) to give a lipid‐layer‐like structure in the crystal.…”

“…Despite this an up to 47 K wide thermal hysteresis loop is observed that can be explained with a hydrogen bond network between the polar head groups of the amphipilic complexes and significant changes in the structure of the complex upon spin transition 1. 5, 17 In contrast to this gradual spin transitions are observed for complexes with relatively short alkyl chain substituents 16. 18 The X‐ray structure of one of those complexes in the HS and the LS state reveals, that the volume change upon spin transition is higher compared to the example with the long alkyl chain.…”

“…In a previous work we showed, that the amphiphilic complexes of this family can self‐assemble to lipid‐layer‐like arrangements,16, 17 with one of those complexes exhibiting a highly cooperative spin transition with a wide hysteresis loop 17. The X‐ray structure of this complex was solved before and after the spin transition, revealing that the volume change of the unit cell is very small (Δ V / V ≈2.9 %),17 and in the region of thermal contraction. Despite this an up to 47 K wide thermal hysteresis loop is observed that can be explained with a hydrogen bond network between the polar head groups of the amphipilic complexes and significant changes in the structure of the complex upon spin transition 1.…”

Weak cooperativity in selected iron(II) 1D coordination polymers

“…Self-assembled coordination polymers (CPs) represent a family of compounds where precisely organised molecular building blocks generate a long range cooperative phenomenon that has effective means of propagation through rigid covalent bonding and flexible supramolecular interactions [4]. Although this situation is usually set for small ligand modules, larger molecular fragments such as dendrimers [5] or extended alkyl chains [6] often show promising SCO profiles without cooperativity loss thus reviewing the selection criteria of ligand topology. We introduce in this context a new module for CPs: 4-(3 -N-phtalimido-propyl)-1,2,4-triazole (phtptrz) (Fig.…”