Precessional Motion in Crystalline Solid Solutions of Ionic Rotors

Abstract

The order-disorder phase transition associated with the uprise of reorientational motion in (DABCOH2) , in the supramolecular salts of general formula [1⋅(DABCOH )]X (where 1=12-crown-4, DABCO=1,4-diazabicyclo[2.2.2]octane, and X=Cl or Br ), has been investigated by variable temperature X-ray diffraction on single crystals and powder samples, as well as by DSC and solid-state NMR spectroscopy (SSNMR). The two compounds undergo a reversible phase change at 292 and 290 K, respectively. The two crystalline materials form solid solutions [1⋅(DABCOH )]Cl Br in the whole composition range (0 < x<1), with a decrease in the temperature of transition to a minimum of ca 280 K, corresponding to x=0.5. Activation energy values for the dynamic processes, evaluated by variable-temperature C magic-angle spinning (MAS) SSNMR and line-shape analysis are ca. 50 kJ mol in all cases. Combined diffraction and spectroscopic evidence has allowed the detection of a novel dynamic process for the (DABCOH ) dications, based on a room temperature precessional motion that is frozen out below the disorder-order transition; to the best of the authors' knowledge this phenomenon has never been observed before.

Solid‐State Dynamics and High‐Pressure Studies of a Supramolecular Spiral Gear

“…It is often assumed that pressure and temperature are in an inverse relation, that is, the effect of the high pressure is comparable to that of low temperature, but this does not necessarily hold, especially in crystals possessing anisotropic compressibility . In the present work, we describe the dynamics of the supramolecular complexes [(12‐crown‐4) 2 ⋅ DABCOH 2 ](X) 2 (X=BF 4 , ClO 4 ; see Scheme ), which are in fact an iteration of the design principles adopted previously . Herein, complexity is added to the system by using tetragonal instead of spherical anions; as a result, discrete structural units are formed, which self‐assemble in a chiral structure.…”

“…We recently showed that weak interactions as well can play as ignificant role. [21] We reported the dynamics of as upramolecular complexo fD AB-COH 2 X 2 (DABCO = 1,4-diazabicyclo[2.2.2]octane, X = Cl or Br) and 12-crown-4, in which chains are formed as represented in Scheme1,c onsisting of the repetition of one molecule of crowne ther,o ne of diprotonated DABCO and counterions.I t was observed that labile attachment of the DABCOH 2 2 + cation bonded,v ia charge-assisted N-H···O bonds, to the crown ether is the driving force in the origin of ac omplex precessional motion, as the DABCOH 2 2 + unit is forcefully tilted with respect to its rotation axis,c ausing af ast andr eversible transition from at etragonal to am onoclinic symmetry,w hich affectst he birefringenceofthe crystals(see Figure 1).…”

“…[24,25] In the present work, we describe the dynamics of the supramolecular complexes [(12-crown-4) 2 ·DABCOH 2 ](X) 2 (X = BF 4 ,C lO 4 ;s ee Scheme1), which are in fact an iteration of the design principles adopted previously. [21] Herein, complexity is added to the system by using tetragonal insteado fs pherical anions;a saresult,d iscrete structuralu nits are formed, whichs elf-assemblei nachiral structure. The solids were investigated by ac ombination of XRD techniques, solidstate NMR spectroscopy,a nd thermala nalyses, showingt hat both the DABCOH 2 2 + cations and the crown ethers undergo fast rotationalm otions.…”

“…So, a loosely packed structure is desirable to lower the activation energy for the rotation and hence increase its frequency. We recently showed that weak interactions as well can play a significant role . We reported the dynamics of a supramolecular complex of DABCOH 2 X 2 (DABCO=1,4‐diazabicyclo[2.2.2]octane, X=Cl or Br) and 12‐crown‐4, in which chains are formed as represented in Scheme , consisting of the repetition of one molecule of crown ether, one of diprotonated DABCO and counterions.…”

Hydrogen‐Bonded Crystalline Molecular Machines with Ultrafast Rotation and Displacive Phase Transitions

“…[18][19][20] The choice of the rotator also plays an essential role in achieving fast intramolecular motion. [21] Globular rotators like bicyclo [2.2.2]octane (BCO), [22] 1,4-diazabicyclo[2.2.2]octane (DABCO), [23,24] p-carborane, [25] or fullerene, [26] might display rotational frequencies faster than those reached with phenylene groups, [27,28] due to their larger size and symmetry that may enable volume-conserving motions. With this in mind, the pairing of the appropriate molecular components should facilitate the development of molecular rotors with fast rotation.…”