Experimental and Theoretical Evidence of a Pb⋅⋅⋅Pb Ditetrel Bond Without a σ‐Hole

Abstract

The crystal structure of a newly synthesized compound, [PbL(Ac)]2, (where L=2 (amino(pyrazin‐2‐yl) methylene) hydrazinecarbothioamide, Ac=acetate anion) exhibits a close contact between pairs of Pb atoms, suggesting a ditetrel bond, in addition to two Pb⋅⋅⋅O tetrel bonds, and two C−H⋅⋅⋅O H‐bonds. The presence of this ditetrel bond as an attractive component is confirmed by various quantum chemical methods. This novelty of this particular bond is its existence even in the absence of a σ‐hole on the Pb atom, which is typically considered a prerequisite for a bond of this type. From a wider perspective, a survey of the Cambridge Structural Database suggests this bond may be more common than was hitherto thought, with 44 examples of Pb⋅⋅⋅Pb contacts amongst a total number of 219 examples of T⋅⋅⋅T interactions in general (T=Si, Ge, Sn, Pb).

A new look at the chalcogen bond: π-hole-based chalcogen (Se, Te) bonding which does not include a σ-hole interaction

“…It is noteworthy that the absence of interactions with a σ-hole has recently been revealed for Pb⋯Pb ditetrel bonding. 66…”

“…It is noteworthy that the absence of interactions with a σ-hole has recently been revealed for Pb⋯Pb ditetrel bonding. 66 The C⋯C/S interactions are structure directing and they are primarily responsible for the stabilization of binding mode b in the structures of (1-3)•ChDA. The orbital interaction (d z 2(Pt) → π*(ChDA)), playing a leading role in the formation of the Ch⋯Pt bond, is also favorable for such structural orientation of ChDA and 1-3, and the back Ch → Pt charge transfer additionally stabilizes this geometry.…”

Does a halogen bond require positive potential on the acid and negative potential on the base?

“…It might be added parenthetically that this same concept of s-holes lying along the extension of a covalent bond applies equally to a number of close cousins of the XB, such as chalcogen, pnicogen, and tetrel bonds, each named according to the column of the periodic table from which the bridging atom is drawn. [18][19][20][21][22][23][24][25][26][27][28][29] Extensive study of the XB has led to a number of general guidelines concerning its strength. Because of the dominating influence of the Coulombic attraction between the positive and negative regions of the acid and base, respectively, the magnification of the potential of either of these units will typically amplify the XB strength.…”

“…It might be added parenthetically that this same concept of σ-holes lying along the extension of a covalent bond applies equally to a number of close cousins of the XB, such as chalcogen, pnicogen, and tetrel bonds, each named according to the column of the periodic table from which the bridging atom is drawn. 18–29…”

Adjusting the balance between hydrogen and chalcogen bonds

“…The halogen bond, for example, occurs when it is Cl, Br, or I in this position, [8][9][10][11][12][13][14][15][16] with analogous designations for pnicogen and tetrel bonds as other classifications. [17][18][19][20][21][22][23][24][25] (First-row atoms like F and N rarely participate in these bonds. 26,27 ) The chief difference with HBs is that unlike the bridging H which is characterized by an overall partial positive charge, the electrostatic potential surrounding the replacement nucleus is more anisotropic and nuanced.…”