Interaction of Lead(II) Perchlorate with N'-Isonicotinoylpicolinohydrazonamide and Its Sodium Salt in the Presence of Potassium Cyanide: Yellow Green Light Emitting Phosphors, Stabilized by Tetrel Bonds, and a System to Transform Methanol to Acetate

Abstract

A coordination polymer is synthesized via the reaction of a mixture of Pb(ClO₄)₂ and KCN with N'-isonicotinoylpicolinohydrazonamide (HL), leading to the formation and stabilization of a {[Pb₃L₃(OAc)(H₂O)](ClO₄)₂}_n·nH₂O (1·nH₂O) network, with the formation and trapping of the acetate anion. Using the sodium N-(amino(pyridin-2-yl)methylene)isonicotinohydrazonate (NaL) instead of HL yields complex [Pb₂L₂OH](ClO₄)·H₂O (2·H₂O) with the formation and trapping of the hydroxide anion. In 1·nH₂O, an almost linear aggregate is produced when the 4-pyridine fragments of the two [PbL]⁺ are coordinated to the metal cation of the third species, joining the three [PbL]⁺ cations. In 1·nH₂O, supramolecular stability is enhanced by Pb···O and Pb···π interactions involving the electron-rich core (Cg) of a ten-membered hydrogen-bonded ring, indicative of tetrel-type bonding. [Pb₂L₂OH]⁺ in 2·H₂O is formed, when a pair of the [PbL]⁺ cations are joined by a hydroxide anion. The Pb···N tetrel bonds bind [Pb₂L₂OH]⁺ to form a zigzag-like 1D supramolecular cationic chain. Both complexes are emissive in methanol. The emission profiles of 1·nH₂O and 2·H₂O in MeOH correspond to CIE-1931 chromaticity coordinates of (0.406, 0.492) and (0.420, 0.498), placing them within the yellow-green region of the visible spectrum. DFT studies are applied to reveal noncovalent interactions, including tetrel bonding, governing the supramolecular architectures. Electrostatic potential and QTAIM analyses confirm the presence of σ-holes at the Pb²⁺ cation in both structures.

1. Synthetic Protocol of Complexes 1 and 2

1

FTIR (top) and ¹H NMR (bottom) spectra of 1·nH₂O ( black) and 2·H₂O (red).

2

A symmetric unit (top) and 1D polymeric chain (bottom) in the crystal structure of 1·nH₂O (ClO₄ ^– anions and the crystal water molecules are not shown for the sake of clarity). Color code: hydrogen atoms in black, carbon atoms in gold, nitrogen atoms in blue, oxygen atoms in red, chlorine atoms in green and lead atoms in magenta.

3

(top) Supramolecular aggregate in the crystal structure of 1·nH₂O (Cg = L _{H33–C33–C32–C31–N13–N12–C30–N15–H15B}···O14_perchlorate). (bottom) The coordination polyhedra are shown. Color code as in Figure .

4

Crystal packing of 1·nH₂O along the a axis (top), b axis (middle) and c axis (bottom).

5

(top) Different views of the {[Pb₂L₂OH]₂(ClO₄)₂}⁻ unit in the crystal structure of 2·H₂O. (middle) A 1D supramolecular chain constructed through the Pb···N and Pb···O tetrel bonds, and N–H···O and O–H···O hydrogen bondsin the crystal structure of 2. (bottom) The coordination polyhedra are shown. Color code as in Figure .

6

Crystal packing of 2·H₂O along the a (top), b (middle) and c (bottom) axes.

7

(top) The absorption (black), emission (red, λ_exc = 380 nm) and excitation (blue, λ_em = 560 nm) spectra for 1·nH₂O (solid line) and 2·H₂O (dashed line) in MeOH at room temperature. (bottom) The absorption (black), emission (red, λ_exc = 370 nm) and excitation (blue, λ_em = 508 nm) spectra for HL (dot line) and NaL (dash-dot line) in MeOH at room temperature. Deconvolution (green) of the emission spectra for 1·nH₂O (solid line, R ² = 0.9970), 2·H₂O (dashed line, R ² = 0.9946), HL (dot line, R ² = 0.9974) and NaL (dash-dot line, R ² = 0.9995) are given.

8

MEP surfaces of the [PbL­(OAc)] fragment of 1·nH₂O (top) and the [Pb₂L₂OH]­(ClO₄) fragment of 2·H₂O (bottom).

9

Combined QTAIM/NCI analysis for 1·nH₂O (left) and 2·H₂O (right). Formation energies of the assemblies are also indicated.

10

(left) Two-dimensional map plot of ∇²ρ combined with the reduced density gradient plot for the dimer of 1. (right) The electron localization function (ELF) represented in a two-dimensional map of the dimer of 1. The two-dimensional map is defined by the Pb3 and N13 atoms of both monomers.