Fine-tuning of thermally induced SCO behaviors of trinuclear cyanido-bridged complexes by regulating the electron donating ability of CCN-terminal fragments

Abstract

To achieve fine regulation of Fe^II SCO behavior, a series of trinuclear cyanido-bridged complexes trans-[CpMe_n(dppe)M^II(CN)]₂[Fe1^II(abpt)₂](OTf)₂ (1–4) (1, M = Fe2 and n = 1; 2, M = Fe2 and n = 4; 3, M = Fe2 and n = 5; 4, M = Ru and n = 5; CpMe_n = alkyl cyclopentadienyl with n = 1, 4, 5; dppe = 1,2-bis-(diphenylphosphino)ethane; abpt = 4-amino-3,5-bis-(pyridin-2-yl)-1,2,4-triazole and OTf = CF₃SO₃⁻) were synthesized and fully characterized by using elemental analysis, X-ray crystallography, magnetic measurements, variable-temperature IR spectroscopy and Mössbauer spectroscopy. It is worth mentioning that different from many mononuclear Fe(abpt)₂X₂ (X = NCS, NCSe, N(CN)₂, C(CN)₃, (NC)₂CC(OCH₃)C(CN)₂, (NC)₂CC(OC₂H₅)C(CN)₂, C₁₆SO₃ and Cl) complexes with more than one polymorph, only one polycrystalline form was found in complexes 1–4. Moreover, the thermally induced SCO behaviors of these four complexes are independent of intermolecular π–π interactions. The electron-donating ability of the C_CN-terminal fragment of CpMe_n(dppe)M^IICN can be flexibly regulated by changing the methyl number (n) of the cyclopentadiene ligand or metal ion type (M^II). These investigations indicate that the electron-donating ability of the C_CN-terminal fragment has an influence on the SCO behavior of Fe1^II. The spin transition temperature (T_1/2) of the complexes decreases with the increase of the electron-donating ability of the fragment CpMe_n(dppe)M^II. This study provides a new strategy to predict and precisely regulate the behaviors of SCO complexes.