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

To achieve fine regulation of FeII SCO behavior, a series of trinuclear cyanido-bridged complexes trans-[CpMen(dppe)MII(CN)]2[Fe1II(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; CpMen = 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 CCN-terminal fragment of CpMen(dppe)MIICN can be flexibly regulated by changing the methyl number (n) of the cyclopentadiene ligand or metal ion type (MII). These investigations indicate that the electron-donating ability of the CCN-terminal fragment has an influence on the SCO behavior of Fe1II. The spin transition temperature (T1/2) of the complexes decreases with the increase of the electron-donating ability of the fragment CpMen(dppe)MII. This study provides a new strategy to predict and precisely regulate the behaviors of SCO complexes.

Co(NCS)2(abpt)2 and Ni(NCS)2(abpt)2 [abpt is 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole]: structural characterization of polymorphs A and B

The synthesis and structures of bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N²,N³]bis(thiocyanato-κN)cobalt(II), [Co(NCS)₂(C₁₂H₁₀N₆)₂] or Co(NCS)₂(abpt)₂, and bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N²,N³]bis(thiocyanato-κN)nickel(II), [Ni(NCS)₂(C₁₂H₁₀N₆)₂] or Ni(NCS)₂(abpt)₂, are reported. In both cases, two polymorphs, A and B, were identified and structurally characterized. For both polymorphs, the structures obtained with the different metals, i.e. Co^II or Ni^II, were found to be isostructural. All of the structures contained an intramolecular N-H...N hydrogen bond, C-H...N interactions and π-π stacking interactions. No structural evidence was observed for a thermal spin crossover for either of the Co(NCS)₂(abpt)₂ polymorphs between 300 (2) and 120 (2) K.