Nature of ambivalence effects in chemical reactivity

Halogen bond directionality translates tecton geometry into self-assembled architecture geometry

“…Both structures feature infinite X-bonded chains in which the nitrogen atoms of the two pyridine rings act selectively as XB acceptors, with no XB involving the oxadiazole core. The observed site selectivity in XB formation parallels the relative basicity of the competing sites 20,21 and is favoured by the greater steric accessibility of the pyridine nitrogens relative to the oxadiazolic core. Exploitation of this site selectivity is currently under investigation to construct novel oxadiazole-based liquid crystalline materials.…”

“…The nC-H absorptions of the pyridine rings are centred at 3045 cm 21 in the pure oxadiazole 1. In 4 and 5 they are blueshifted to 3047 and 3051 cm 21 , respectively, and also become less intense than in pure 1 consistent with a higher positive charge on the pyridyl hydrogens in the complexes. 12a A blue-shift is observed also for the bands associated with the pyridine ring breathing vibrations (at 1543 and 1487 cm 21 in pure 1, at 1545 and 1489 cm 21 in 4, and at 1549 and 1492 cm 21 in 5).…”

“…19 Single crystal X-ray analyses of 4 and 5 reveal that short I … N XBs involving pyridyl nitrogen atoms are the attractive noncovalent interactions largely responsible for the cocrystals' formation. In fact, while the nitrogen atom in position four of the oxadiazole ring has a nucleophilic or weakly basic character 20 and the nitrogen in position two has an amphiphilic 21 character, no XB involves the azole ring. XB selectively involves the two pyridyl nitrogen atoms of 1 which give I … N contacts in the range 2.77-2.88 Å.…”

Oxygen-Donor Metalloligands Induce Slow Magnetization Relaxation in Zero Field for a Cobalt(II) Complex with {CoO4} Motif

“…Results from this study can also be placed in a more general context related to the reactivity of O-donor-containing transition metal complexes that act as catalysts in charge transfer-type reactions. Specifically, second-coordination sphere effects on O-donor ligation, e.g., by coordination of additional metal ions, may induce ambivalence in the O-donor properties at the active site . When combined with vibronic coupling, this aspect may become important in both homogeneous and heterogeneous catalysis and may be analyzed and exploited both spectroscopically and by theoretical means.…”

“…Specifically, second-coordination sphere effects on O-donor ligation, e.g., by coordination of additional metal ions, may induce ambivalence in the O-donor properties at the active site. 63 When combined with vibronic coupling, this aspect may become important in both homogeneous and heterogeneous catalysis and may be analyzed and exploited both spectroscopically and by theoretical means. 53 were prepared following literature procedures.…”