ABSTRACT
Two new salts of a mononuclear tripodal Fe(II) complex were prepared, using ClO4- and Cl-. The ClO4- sample (1) remained HS at low temperatures, similar to the previously reported BF4- analogue. Crystallising with the Cl- anion (2) led to a markedly different crystal packing arrangement, and engendered SCO activity. This has been correlated to the lower crystal packing density in 2 and the coordination complex conformational differences arising due to the packing motifs of 1 and 2. Further, solvent ordering effects have been proposed to facilitate spin transition behaviour in 2.
ABSTRACT
We present five new dinuclear triple helicate compounds of types [Mn2L3](ClO4)4, [Co2L3](BF4)4, [Ni2L3](BF4)4, [Cu2L3](BF4)4, and [Zn2L3](BF4)4, where L is a previously reported semi-rigid ligand incorporating two α-diimine primary donor groups and two secondary 4-pyridyl donor groups. All complexes have been characterized in both solution and the solid state. Single crystal X-ray diffraction studies were used to probe the variation in the respective helical structures as the coordinated metal ion was altered, including the effect on the orientations of the secondary binding domains. The influence of the metal ion size, the spin state in the case of Fe(II), and the presence of Jahn-Teller distortions on the overall helical structure has been investigated. These results form a basis for the design and construction of new large metallosupramolecular architectures which manifest properties associated with the constituent helical metalloligand units.
ABSTRACT
Discrete spin crossover (SCO) heteronuclear cages are a rare class of materials which have potential use in next-generation molecular transport and catalysis. Previous investigations of cubic cage [Fe8 Pd6 L8 ]28+ constructed using semi-rigid metalloligands, found that FeII centers of the cage did not undergo spin transition. In this work, substitution of the secondary metal center at the face of the cage resulted in SCO behavior, evidenced by magnetic susceptibility, Mössbauer spectroscopy and single crystal X-ray diffraction. Structural comparisons of these two cages shed light on the possible interplay of inter- and intramolecular interactions associated with SCO in the NiII analogue, 1 ([Fe8 Ni6 L8 (CH3 CN)12 ]28+ ). The distorted octahedral coordination environment, as well as the occupation of the CH3 CN in the NiII axial positions of 1, prevented close packing of cages observed in the PdII analogue. This led to offset, distant packing arrangements whereby important areas within the cage underwent dramatic structural changes with the exhibition of SCO.
