Structural investigations of a lead(iv) tetraacetate–pyridine complex

Abstract

A 1 : 1 crystalline complex of lead(IV) tetraacetate and pyridine (LTA-py) has been prepared. The single-crystal X-ray structure, at 296 and 150 K, establishes the presence of a relatively short Pb-N bond (2.307 A) within an intriguing seven-coordinate lead inner sphere consisting of the pyridine ligand and two bidentate and two monodentate acetate ligands. The pyridine occupies a surprising amount of the available coordination space and has induced a dramatic change in coordination compared to the four chelating acetate ligands found in lead tetraacetate (LTA). Thermal measurements (TGA/DSC) indicate the de-coordination of pyridine and its loss from the solid between 360 and 380 K. (207)Pb CP/MAS NMR spectroscopy also demonstrates the existence of the Pb-N bond through observation of (1)J((207)Pb,(14)N)= 63 Hz and a (207)Pb-(14)N dipolar coupling constant, of 149 Hz. The solid-state (207)Pb NMR parameters are used to give insight into the coordination environment of Pb(iv) in LTA-py. In solution, ligand exchange is rapid on chemical shift and J-coupling time scales. A (207)Pb NMR study of the titration of an LTA solution by pyridine yields a stability constant for LTA-py of K = 1.5 M(-1) and predicts it to have a (207)Pb NMR chemical shift essentially identical to that observed by CP/MAS NMR in the solid state. This correlation between the solid state and solution indicates that the seven-coordinate LTA-py structure found in the crystalline state does persist in solution, and this could further explain why the addition of pyridine has such profound effects on lead(IV) carboxylate-mediated organic reactions. Simulations of exchange-broadened line shapes of (13)C CP/MAS NMR spectra in the temperature regime above 280 K indicate local motion of the pyridine rings in the form of 180 degrees jumps (activation energy 72.5 kJ mol(-1)); these are first such ring flips reported for a coordinated pyridine ligand.

Cyclodextrin Bucket Wheels: An Oligosaccharide Assembly Accommodates Metal(IV) Centers

“…A good example is lead(IV), whose coordination chemistry in water is restricted to a couple of halogeno plumbates(IV) in acidic solution, and the hexahydroxidoplumbate(IV) ion at high pH values. In line with this experience, the lead(IV) compounds used in synthetic organic chemistry, lead tetraacetate and its derivatives, rapidly decompose on contact with moisture to form black lead dioxide 1. Attempts to prepare chelates by adding potential chelators such as oxalate, catecholate, or glycosides to hexahydroxidoplumbate(IV) solutions result in the formation of mostly brownish suspensions of decomposition products.…”

Effect of Co-Ordination Chemistry and Oxidation State on the 207Pb Magnetic-Shielding Tensor: A DFT/ZORA Investigation

“…The various classes of lead co-ordination compounds have solid-state nuclear magnetic (SSNMR) fingerprints. , In general, 207 Pb SSNMR spectra of hemidirected lead­(II) co-ordination systems show chemical-shift tensors with large spans (Ω) due to the asymmetric electron density distribution around the lead site. ,− For such materials, the skew (κ) of the 207 Pb shielding tensor tends to be positive and close to 1.00, indicating the existence of a significantly shielded unique principal component of the chemical-shift tensor. By comparison, 207 Pb SSNMR measurements of holodirected lead­(II) systems exhibit a tensor that has a smaller span than for hemidirected sites. ,,,, The 207 Pb SSNMR literature for lead­(IV) systems is sparser than for lead­(II), but reported investigations suggest that these sites generally have small chemical-shift spans, similar to holodirected lead­(II) sites. − In addition, the range of isotropic 207 Pb chemical shifts of lead­(IV) sites is, in general, smaller than that of either hemidirected or holodirected lead­(II) sites.…”

On-surface assembly of low-dimensional Pb-coordinated metal–organic structures

“…[1][2][3] These characteristics provide opportunities for constructing Pb-based MOFs that exhibit rich structural topologies and diverse coordination geometries. [4][5][6][7][8][9][10][11] Moreover, the unique electronic configuration of Pb makes the Pb-based MOFs potential electroluminescent devices, light-emitting diodes and fluorescent sensors. [9][10][11] Recently, it was demonstrated theoretically that a Pb-based two-dimensional (2D) organometallic structure exhibits a non-trivial quantum state, known as the topological insulator phase, due to the strong spin-orbit coupling effects of the heavy Pb atoms.…”

“…[4][5][6][7][8][9][10][11] Moreover, the unique electronic configuration of Pb makes the Pb-based MOFs potential electroluminescent devices, light-emitting diodes and fluorescent sensors. [9][10][11] Recently, it was demonstrated theoretically that a Pb-based two-dimensional (2D) organometallic structure exhibits a non-trivial quantum state, known as the topological insulator phase, due to the strong spin-orbit coupling effects of the heavy Pb atoms. 12 This prediction hints that the Pb-coordinated 2D metal-organic structures may represent a new family of functional materials with appealing electronic and spintronic properties.…”