Inversion Symmetry Breaking in Order–Disorder Transitions of Globular Ligands Coordinating to Cobalt(II) and Nickel(II) Bisacetylacetonato Complexes During Heating

Abstract

Unexpectedi nversion-symmetry breakingw as observed in the order-disorderp hase transitions of [M(acac) 2 (abco) 2 ](1;M = Co 2 + , 2;N i 2 + ,a cac À = 2,4-pentanedionato, abco = 1-azabicyclo-[2.2.2]-octane = quinuclidine) during heating. The isostructural, transition-free complexes [M(acac) 2 (cabco) 2 ](3;M = Co 2 + , 4;N i 2 + ,c abco = 3-chloro-1azabicyclo-[2.2.2]-octane = 3-chloroquinuclidine) were also studiedf or comparison. Complexes 1 and 2 crystallized in orderedp hases in the centrosymmetric I2/m space group at 100 K, whereas they crystallizedi nd isorderedp hases in the non-symmetric I2s pace group at 300 K. The 608 step rotation disorderingo ft he abco ligandsw as observedi nt he electron density maps of 1 and 2,w hichw as consistent with the transition enthalpies estimated by differential scanning calorimetry (DSC). Gradual phase transitions were observed for 1 and 2 by DSC and powder X-ray diffraction (PXRD) at approximately 225 K. The inversion-symmetry disordering was likely induced by the local pseudo-symmetry of the abco ligands, increasing from trigonal to hexagonal and the increased steric repulsion pathways among them.

Ionic Conductivities Induced by the Partial Solvent Molecule Removal from Diruthenium(II,III) Adamantanecarboxylate Salts

“…It should be distinguished from the case of perfect racemic twinning, in which the noncentrosymmetric structure was successfully refined with Flack x = 0.5. 14 Globular molecular groups, such as adamantyls, sometimes exhibit rotational or vibrational fluctuations at relatively high temperatures. The electron density maps of 1 were generated using the X-ray data acquired at 118 and 300 K to study the thermal fluctuations (Figure 4).…”

“…This suggests that the pair of MeOH molecules and BF 4 – ions were randomly placed at the neighboring sites without the formation of local chiral domains. It should be distinguished from the case of perfect racemic twinning, in which the noncentrosymmetric structure was successfully refined with Flack x = 0.5 …”

“…8 In the crystal, as the molecules are orientationally disordered, the crystal defects and diffusions increase, and it becomes plastic. Linear alkyl chains and globular substituents also exhibit uniaxial rotations in crystals 9,10 and often affect the physical properties of the solids, such as thermal conductivities, 11 birefringences, 12,13 chirality, 14 and dielectricities. 15,16 In this work, we prepared dinuclear Ru(II,III) paddlewheels bearing substituted adamantyl groups as molecular rotators (Figure 1).…”

“…In the crystal, as the molecules are orientationally disordered, the crystal defects and diffusions increase, and it becomes plastic. Linear alkyl chains and globular substituents also exhibit uniaxial rotations in crystals , and often affect the physical properties of the solids, such as thermal conductivities, birefringences, , chirality, and dielectricities. , In this work, we prepared dinuclear Ru­(II,III) paddlewheels bearing substituted adamantyl groups as molecular rotators (Figure ). They have been reported as useful functional building blocks with electron acceptability and magnetic anisotropy, and various functional metal–organic frameworks have been reported from their combinations with the bridging ligands coordinating to the axial sites of the Ru­(II,III) 2 ions. − However, we found that the crystals of the discrete paddlewheels 1 – 3 also exhibit ionic conductivity along with the partial removal of the crystal solvent molecules.…”

Ferroic phase transition molecular crystals

“…5d), 86 showing unique inverse temperature symmetry breaking. [87][88][89][90] The dumbbell-shaped molecular rotor consists of Zn-salen as the stator and 1,4-diazabicyclo[2.2.2]octane as the rotator. Anisotropic steric repulsions among the molecules trigger a concerted molecular movement resulting in the unique ferroelastic phase transition at 263 K (low-temperature phase Cmca ↔ high-temperature phase P2 1 /c).…”