A new series of iron(II) 1D coordination polymers with the general formula [FeL1(pina)]·xsolvent with L1 being a tetradentate N2O2(2-) coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentanedionato)(2-)-N,N',O(2),O(2)'], and pina being a bridging axial ligand N-(pyrid-4-yl)isonicotinamide, are discussed. The X-ray crystal structure of [FeL1(pina)]·2MeOH was solved for the low-spin state. The compound crystallizes in the monoclinic space group P21/c, and the analysis of the crystal packing reveals the formation of a hydrogen bond network where additional methanol molecules are included. Different magnetic properties are observed for the seven samples analyzed, depending on the nature of the included solvent molecules. The widest hysteresis loop is observed for a fine crystalline sample of composition [FeL1(pina)]·xH2O/MeOH. The 88 K wide thermal hysteresis loop (T1/2↑ = 328 K and T1/2↓ = 240 K) is centered around room temperature and can be repeated without of a loss of the spin transition properties. For the single crystals of [FeL1(pina)]·2MeOH, a 51 K wide hysteresis loop is observed (T1/2↑ = 296 K and T1/2↓ = 245 K) that is also stable for several cycles. For a powder sample of [FeL1(pina)]·0.5H2O·0.5MeOH a cooperative spin transition with a 46 K wide hysteresis loop around room temperature is observed (T1/2↑ = 321 K and T1/2↓ = 275 K). This compound was further investigated using Mössbauer spectroscopy and DSC. Both methods reveal that, in the cooling mode, the spin transition is accompanied by a phase transition while in the heating mode a loss of the included methanol is observed that leads to a loss of the spin transition properties. These results show that the pina ligand was used successfully in a crystal-engineering-like approach to generate 1D coordination polymers and improve their spin crossover properties.

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.

In this paper the X-ray structure and magnetic properties of iron(II) acetate -starting material for the synthesis of a wide range of iron complexes -are presented. The compound crystallises in the space group Pbcn and was identified as 2D coordination polymer consisting of iron atoms and acetate moieties with all the iron atoms hexacoordinate and different coordination modes for the acetate moieties. Additional hydrogen bond contacts lead to a porous coordination polymer

The synthesis and characterisation of four new Schiff base‐like ligands with long alkyl chains in the outer periphery and their iron(II) complexes with methanol and pyridine as axial ligands is reported. Two of the methanol complexes crystallise in a lipid layer‐like arrangement with the alkyl chain (tail) packed in the middle and the iron centres (head) in the outer sites. The pyridine complexes show varying types of spin transition (step wise, incomplete, with hysteresis), which depends on the alkyl chain length and substituents in the outer periphery of the ligand. Investigations in solution using 1H NMR spectroscopy demonstrate that the differences in the spin transition behaviour are due to packing effects as the same transition curve is obtained independently of the alkyl chain length.

Several new amphiphilic iron complexes were synthesised and characterised by single crystal X-ray structure analysis. The Schiff-base-like equatorial ligands contain long alkyl chains in their outer periphery with chain lengths of 8, 12, 16 and 22 carbon atoms. As axial ligands methanol, pyridine, 4-aminopyridine, 4-(dimethylamino)pyridine and 1,2-bis(4-pyridyl)ethane were used. X-ray structure analysis of the products reveals different coordination numbers, depending on the combination of equatorial and axial ligand. The driving force for this is the self-assembly to lipid-layer-like arrangements. This can be controlled through the chain lengths and the dimension of the axial ligands in a crystal-engineering-like approach. For this an empirical rule is introduced concerning the crystallisation behaviour of the complexes. The efficacy of this rule is confirmed with the crystallisation of an octahedral complex with two docosyl (C22) chains in the outer periphery. The rule is also applied to other ligand systems.