| Abstract |
In this work, we report extensive experimental and theoretical investigations on a new series of Pb(II)coordination polymers exhibiting extended supramolecular architectures, namely [Pb-2(L-I)(NCS)(4)](n)(1), [Pb(HLII)I-2](n)(2), [Pb(L-III)I](n)(3) and [Pb(HLIV)(NO3)(2)](n)center dot nMeOH (4), which were self-assembled from different Pb(II)salts and various pyridine-hydrazine based linkers, namely 1,2-bis(pyridin-3-ylmethylene)hydrazine (L-I), (pyridin-4-ylmethylene)isonicotinohydrazide (HLII), 1-(pyridin-2-yl)ethylidenenicotinohydrazide (HLIII) and phenyl(pyridin-2-yl)methylenenicotinohydrazide (HLIV), respectively. It is recognized that the origin of self-assembling is fundamentally rooted in a dual donor (6s(2)/6p(0) hybridized lone electron pair) and electrophilic behaviour of Pb-II. This allows production of extended topologies from a 1D polymeric chain in 4 through a 2D layer in 2 to the 3D frameworks in 1 and 3, predominantly due to the cooperative action of both covalent and non-covalent tetrel interactions of the overall type Pb-X (X = O, N, S, I). Counterintuitively, the latter, seemingly weak interactions, have appeared to be even stronger than the typical covalent bonds due to the presence of a bunch of supportive London dispersion dominated contacts: pi center dot center dot center dot pi, Lp center dot center dot center dot pi, C-H center dot center dot center dot O, C-H center dot center dot center dot I, C-H center dot center dot center dot H-C as well as more typical mainly electrostatically driven N-H center dot center dot center dot O or N/O-H center dot center dot center dot O hydrogen bonds. It is revealed that the constituting generally strong tetrel type Pb-X (X = O, N, S, I) bonds, though dominated by a classic Coulomb term, are therefore characterized by a very important London dispersion constituent, extremely strong relativistic effects and the two way dative-covalent Pb <-> X electron charge delocalization contribution as revealed by the Extended Transition State Natural Orbital for Chemical Valence (ETS-NOCV) charge and energy decomposition scheme. It unravels that the pyridine-hydrazine linkers are also excellent London dispersion donors, and that together with the donor-acceptor properties of the heavy (relativistic) Pb-II atoms and nucleophilic counterions lead to extended self-assembling of 1-4. |
