Spin crossover in di-, tri- and tetranuclear, mixed-ligand tris(pyrazolyl)methane iron(ii) complexes?

Dalton Transactions Pub Date: 2011-06-06 DOI: 10.1039/C0DT01725F

Abstract

A series of polynuclear mixed-ligand tris(pyrazolyl)methane iron(II) complexes displaying high temperature spin crossover behaviour has been synthesised. These complexes are of the type [(Fe((3,5-Me2pz)3CH))n(μ-L)](BF4)2n, where μ-L is one of five bridging ligands X(CH2OCH2C(pz)3)n, (X = the central linking moiety, pz = pyrazolyl ring and n = 2 (ditopic), 3 (tritopic) or 4 (tetratopic)). Throughout the series the terminal tris(3,5-dimethylpyrazolyl)methane co-ligand (3,5-Me2pz)3CH and the BF4? counter anion were kept constant while variations in the central linking moiety have produced three dinuclear complexes and a trinuclear and tetranuclear complex, all isolated as solvates. The three dinuclear complexes are a 1,4-xylene-bridged complex 1·2DME, a 2,6-naphthalene-bridged complex 2·2.5MeCN.2DME and a 1,4-butene-bridged complex 3·2DME. The trinuclear complex 4·solvent (solvent undefined) has a 1,3,5-mesitylene core and the tetranuclear complex, 5·8MeCN.2tBuOMe, has a 1,2,4,5-tetramethylbenzene core (DME = dimethoxyethane, tBuOMe = tertiarybutyl-methylether). The trinuclear cluster has a “3-up” cup shape with the cups arranging themselves in pairs to form capsules that contain anion guests. All the solvated compounds have been structurally characterised and both the solvated and desolvated versions have had their magnetic and thermal properties thoroughly investigated by variable temperature magnetic susceptibility, differential scanning calorimetric and M?ssbauer spectral methods. They all display typical low spin iron(II) magnetic behaviour at room temperature and all undergo a spin state transition to high spin iron(II) above room temperature. In particular, complex 1·2DME shows an abrupt spin transition which shifts, upon desolvation, to a lower value of T1/2 and in addition displays a small thermal hysteresis.

Graphical abstract: Spin crossover in di-, tri- and tetranuclear, mixed-ligand tris(pyrazolyl)methane iron(ii) complexes
Recommended Literature