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

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 = CF 3 SO 3 - ) 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) 2 X 2 (X = NCS, NCSe, N(CN) 2 , C(CN) 3 , (NC) 2 CC(OCH 3 )C(CN) 2 , (NC) 2 CC(OC 2 H 5 )C(CN) 2 , C 16 SO 3 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 II CN 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.