Alkali Metal Complexes of Aromatic Polycarboxylates—a Balance of π-Stacking and Coordinate Bonding Interactions?

Solid‐State Luminescence and π‐Stacking in Crystalline Uranyl Dipicolinates

“…An explanation of the difference in these alkali metal arrays may be that only Rb is involved in coordinative interaction with uranyl-O [Rb-O 3.035(6) Å]. As seems to be commonly the case with heavy and apparently weakly coordinating metals, [6,21,[27][28][29][30][31] it is difficult to define a precise cutoff distance for interactions considered to be bonding but the coordination numbers of both Rb and Cs here appear to be high, involving O-donors only, with rather irregular geometry about the metals. Interestingly, the extreme M···O separations approach those of M···U, which, if they are correctly considered as contacts of closed-shell species of similar charge, would be regarded as involving negligible interactions, thus indicating that the extreme M···O contacts must also be of little significance.…”

“…[1][2][3][4][5] Related ligands such as chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) and benzimidazole derivatives of dipicolinate also display interesting coordination properties. [6,7] Dipicolinic acid and its anions appear to bind well to all metals in the periodic table, though specific properties such as the strong luminescence of Eu III and Tb III [8] and the biological activity of transition-metal complexes [3,9,10] have led to a strong focus in certain areas and to a relative neglect of actinide complexation. Nonetheless, in the specific case of the uranyl ion, a variety of species, [11][12][13][14] including the remarkable helical polymer, [UO 2 (dipic)(OH 2 )] n , [15] has long been known and has recently been significantly expanded, principally through the characterisation of several binuclear complexes.…”

Lead(II): misleading or merely hermaphroditic?

“…4a), though both show close atom approaches~3.47 Å, typical of systems conventionally described as being involved in p-p stacking [26,27], though the actual nature of the projection shows a further variation on those known for coordinated phenanthroline in other Pb(II) complexes [15]. Presumably, such differences in projection are the consequences of other interactions involving the ligands (a parallel to the behaviour of aromatic ligands such as picrate [28] and various others [29]), the most obvious of these being N-and C-coordination to Pb, though there are several close contacts of other forms apparent, including 'edgeto-face' approaches associated with partial interlocking of the two phenanthroline arrays (Fig. 4b).…”

2,6-Bis(2-methyl-1,3-diazinan-2-yl)pyridine

“…For 2,6-diacetylpyridine, see: Burnet et al (2003) and for 1,3diaminopropane, see: Thalladi et al (2000).…”