Template synthesis, structure and electropolymerization of the 2-thiopheneboron-capped cobalt(II) clathrochelates

Synthesis and Temperature-Induced Structural Phase and Spin Transitions in Hexadecylboron-Capped Cobalt(II) Hexachloroclathrochelate and Its Diamagnetic Iron(II)-Encapsulating Analogue

“…The nitrogen and oxygen atoms of the LS molecule of Co(Cl 2 Gm) 3 (Bn-C 16 H 33 ) 2 are not equally populated; the maxima of the spin density are localized on the atoms of its ribbed chelate fragment, giving the longest Co−N bond. This explains the observation of superhyperfine interaction with only two 14 N nuclei in the EPR spectrum of the LS complex. In contrast, in the HS molecule of this cobalt(II) complex, the spin density is almost equally distributed close to its Co−N bonds and oxygen atoms of the donor oxime groups.…”

“…The SCO behavior of the molecular compounds in the solid state can be regarded as a competition between long-range cooperative and short-range anticooperative interactions, with stacking − and van der Waals bonding ,, typically regarded as anticooperative supramolecular interactions. So, gradual single-step SCO for the clathrochelate Co­(Cl 2 Gm) 3 (BThioph) 2 can be assigned to the anticooperative effect of the π···S interactions in its crystals. In the isostructural crystals Co­(Cl 2 Gm) 3 (B n -C 4 H 9 ) 2 and Co­(Br 2 Gm) 3 (B n -C 4 H 9 ) 2 , the infinite π···Hal bonded chains with the shortest plane···dot distances of approximately 3.2–3.5 Å can be distinguished: the fine-crystalline samples of these n -butylboron-capped cobalt­(II) hexahalogenoclathrochelates exhibit gradual SCO due to anticooperativity effects.…”

“…The magnetometry data, however, suggested the preferable population of the LS state of this clathrochelate in the solid state at low temperatures. Given that only substitution of the clathrochelate ligand by six halogen atoms − resulted in a sufficiently weak ligand field to make HS ↔ LS transitions possible, here we report the synthesis, single-crystal X-ray structures, SCO and phase transition behavior, and magnetic, spectral, and redox properties of the hexadecylboron-capped cobalt­(II) hexachloroclathrochelate compared with its iron­(II)-containing analogue; note that such metal hexahalogenoclathrochelates are also reported , to be very efficient electrocatalysts for hydrogen production.…”

Spin-Crossover Anticooperativity Induced by Weak Intermolecular Interactions

“…Out of more than 30 known cobalt(II) clathrochelates (see reference in the SI), only those with six chlorine atoms in their chelate fragments can become high-spin, 18 and some of them demonstrate a complete SCO without any detectable cooperativity. 29 Thus, the anticooperative effects observed are due to some specific intermolecular interactions that effectively stabilize the LS state of the complex.…”

“…The comparison of the crystal structures of similar compounds shows that all complexes with the stabilized LS state share the same weak π•••Cl interactions (Figure 5 and Figure S9 in the SI). Disrupting these interactions by either including solvent molecules into the crystal lattice 18 or by using apical substituents preventing the close packing of macrobicylic ligands 29 (Figure S10 in the SI) leads to the gradual and complete SCO without extra stabilization of the LS state. Although the average energy of these π•••Cl interactions (estimated from X-ray diffraction data; see the SI for more details) is only 1.2 kcal/mol, the resulting weak stabilization is quite significant in comparison with the enthalpy of this LS↔ HS transition in solution (1.7 kcal/mol using simple Boltzmann model), which explains the observed changes in the SCO curves.…”