DABCO molecule in the M2(C8H4O4)2·C6H12N2 (M = Co, Ni, Cu, Zn) metal-organic frameworks

Overview of Low-Temperature Heat Capacity Data for Zn2(C8H4O4)2.C6H12N2 and the Salam Hypothesis

“…The entropy of the phase transitions is shown in Table 2. The obtained data indicate that the absorbed atoms of 4 He affect the states of D 3 (S) and D 3 (R) forms of DABCO (phase transitions~14 and~60 K) and do not affect the ordering and disordering of BDC 2− anions during the phase transition at 130 K. This result can be explained by the fact that the structure of DABCO is flexible [23,24] as compared to that of BDC 2− anions and can therefore be deformed in the presence of adjoining 4 He atoms, whereas the structure of BDC 2− anions remains unchanged.…”

“…Also, a quasi-D 3h form of DABCO is possible due to strong vibrations of the molecule around the C 3 axis. The molecules with the D 3 symmetry, which can be left-twisted D 3 (S) or right-twisted D 3 (R), are considered to be chiral isomers (enantiomers) [4]. the D3 symmetry, which can be left-twisted D3(S) or right-twisted D3(R), are considered to be chiral isomers (enantiomers) [4].…”

“…The vertical edges are formed by DABCO molecules (linkers), the point symmetry of which does not contain a 4-fold rotational symmetry axis (Figure 1). This is the reason why DABCO molecules are orientationally disordered; moreover, D3(S) and D3(R) forms can transform into each other (by activation or tunneling) [4,6]. Calorimetry, nuclear magnetic resonance, and X-ray structural analysis data provide evidence of the presence of phase transitions in Zn-DMOF at ~14, ~60, and ~130 K [7][8][9][10][11][12].…”

Chirality and Relativistic Effects in Os3(CO)12

“…The barrier between D3S and D3R is low (~10-14 kJ/mol). Thus, similarly to the DABCO molecule [1], at room temperature there should be a dynamical equilibrium between D3S and D3R structures resulting in a quasi-D3h structure. The main difference between experimental XRD data and relativistic calculations (for both SR and SO methods) is found in the dihedral angles ∠C-Os-Os-C и∠C 3axes -Os-C, which characterize the degree of the twisting of the Os 3 (CO) 12 structure.…”

“…Many essential biological and chemical processes are stereoselective, involving only one enantiomer, which exists independently from its chiral counterpart. Separation of one enantiomer from another is not only important for practical use, but also sparks much interest as a fundamental problem, which constantly attracts research attention to the spatial and electronic structure of enantiomers [1][2][3]. In particular, especially interesting is how the parity violating weak nuclear forces may manifest in chiral molecules and may be somehow responsible for the choice of which enantiomer would prevail in living organisms [4][5][6][7].…”