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In this work we report a new PbII coordination polymer [Pb3L2(N3)4] n , which was obtained from Pb(N3)2 and 1-(pyridin-2-yl)ethylidenepicolinohydrazide (HL). The complex exhibits a 1D polymeric chain, constructed from the {[Pb3(N3)4]2+}n backbone, decorated with deprotonated organic L− ligands. The latter ligands are pentadentate and link two metal cations. The PbII ions were found to be in a N5O or N5O2 coordination environment, formed by covalent bonds. The azide ligands either bind four metals in a μ4-1,1,3,3 coordination mode or are coordinated to metal centers as terminal ligands. All the metal centers exhibit a hemidirected coordination geometry with a pronounced coordination gap, which allows the close approach of an additional nitrogen atom arising from an adjacent terminal azide ligand. A simplified underlying network of [Pb3L2(N3)4] n , without considering Pb⋯N tetrel bonds, exhibits the tetranodal 3,4,4,4-connected chain topology, while considering all Pb⋯N tetrel bonds, the binodal 4,5-connected chain topology was shown. The crystal packing of [Pb3L2(N3)4] n is reinforced by intermolecular π⋯π stacking interactions, formed by PbII-based five-membered chelate metallocycles and pyridine rings. In-depth bonding analysis using ETS-NOCV, IQA and NCI methods demonstrates that although the azide anions experience significant steric crowding due to repulsive azide–azide interactions, they are engaged in strong attractive, Coulomb dominated, dative-covalent Pb–N and tetrel-type Pb⋯N connections, which are further augmented by weak exchange–correlation driven C–H⋯N hydrogen bonds as well as London dispersion forces due to metallocycle units. The diffuse reflectance spectrum of [Pb3L2(N3)4] n revealed a broad band with two maxima in the UV region, corresponding to intraligand transitions, and an intense shoulder in the visible region, corresponding to metal-to-ligand charge-transfer. The latter shoulder explains the observed yellow colour of the complex. [ABSTRACT FROM AUTHOR]

In this work, we report extensive experimental and theoretical investigations on a new series of PbII coordination polymers exhibiting extended supramolecular architectures, namely [Pb2(LI)(NCS)4]n (1), [Pb(HLII)I2]n (2), [Pb(LIII)I]n (3) and [Pb(HLIV)(NO3)2]n·nMeOH (4), which were self-assembled from different PbII salts and various pyridine-hydrazine based linkers, namely 1,2-bis(pyridin-3-ylmethylene)hydrazine (LI), (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 (6s2/6p0 hybridized lone electron pair) and electrophilic behaviour of PbII. 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: π⋯π, Lp⋯π, C–H⋯O, C–H⋯I, C–H⋯H–C as well as more typical mainly electrostatically driven N–H⋯O or N/O–H⋯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) PbII atoms and nucleophilic counterions lead to extended self-assembling of 1–4. [ABSTRACT FROM AUTHOR]