Synthesis, Structure Determination from Powder Diffraction Data, and Thermal Behavior of Lead Zirconium Oxalate Hydrate Pb₂Zr(C₂O₄)₄·nH₂O (3 < n < 9)

Abstract

A new mixed lead zirconium oxalate, Pb 2 Zr(C 2 O 4 ) 4 ‚nH 2 O (3 < n < 9), has been prepared from precipitation of a nitric solution of lead and zirconium cations by an oxalic solution at 345 K. The crystal structure of Pb 2 Zr(C 2 O 4 ) 4 ‚6H 2 O has been determined ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is monoclinic, space group C2/c (No. 15), cell dimensions a ) 9.537(1) Å, b ) 29.622(3) Å, c ) 8.9398(9) Å, β ) 121.19(4)°, and Z ) 4. The complex three-dimensional structure is built from 8-fold-coordinated zirconium atoms and 9-fold-and 8-fold-coordinated lead atoms linked by oxalate groups. Only one water molecule has been found free in the structure. The dehydration is reversible, and the cell parameters vary between the composition limits without a major change of the crystal structure framework. A thermodynamical study has demonstrated the zeolitic nature of the water molecules. The enthalpy, ∆ r H, and entropy, ∆ r S, of the dehydration reaction have been determined as a function of the number of zeolitic water molecules. The complete decomposition scheme of the anhydrous phase Pb 2 Zr(C 2 O 4 ) 4 into PbZrO 3 and finally ZrO 2 , studied from temperature-dependent X-ray powder diffraction and thermogravimetric analysis, is carefully described.

Metal Carboxylates with Open Architectures

“…These compounds contain MO 8 (M=Zr, Cd) polyhedral units with dodecahedral or distorted square‐antiprismatic geometry that are linked through oxalate oxygen atoms to give 3D open frameworks. In [Pb 2 Zr(ox) 4 ]⋅ n H 2 O, {PbO 8 } and {PbO 9 } units form two independent chains linked through the oxalate groups and the isolated {ZrO 8 } polyhedron to form a 3D structure 47c. The zeolite‐like storage of water molecules in the channels of some of these compounds has also been examined and the influence of water content on the lattice parameters has been studied.…”

Offene Metallcarboxylat‐Architekturen

“…In diesen Verbindungen liegen dodekaedrische oder verzerrt quadratisch‐antiprismatische {MO 8 }‐Polyeder (M=Zr, Cd) vor, die über Oxalat‐Sauerstoffatome miteinander verbunden sind und so offene dreidimensionale Gerüste bilden. In [Pb 2 Zr(ox) 4 ]⋅ n H 2 O bilden die {PbO 8 }‐ und {PbO 9 }‐Einheiten zwei unabhängige Ketten, die durch Oxalatliganden und isolierte {ZrO 8 }‐Polyeder miteinander zu dreidimensionalen Strukturen verknüpft sind 47c. Die Zeolith‐analoge Einlagerung von Wassermolekülen in die Kanäle einiger dieser Verbindungen wurde ebenso untersucht wie der Einfluss des Wassergehalts auf die Gitterkonstanten.…”

catena-Poly[N-methylpiperazinium(2+) [[bis(oxalato-κ2O,O′)zirconate(IV)]-μ2-oxalato-κ4O,O′:O′′,O′′′]]

“…In common with other metals, zirconium oxalate complexes can serve as precursors in the preparation of ternary oxides; among these are some species having four oxalate groups attached to the Zr atom, for example, Na 4 [Zr(C 2 O 4 ) 4 ]Á3H 2 O (Glen et al, 1963), K 4 [Zr(C 2 O 4 ) 4 ]Á.5H 2 O (Kojić-Prodić et al, 1978), Ba 2 [Zr(C 2 O 4 ) 4 ]Á3H 2 O (Vertruyen et al, 2004) and Pb 2 [Zr(C 2 O 4 ) 4 ]ÁnH 2 O (Boudaren et al, 2000). The ammonium salt formulated as (NH 4 ) 2 [CdZr(C 2 O 4 ) 4 ]Á4H 2 O has distinct [Zr(C 2 O 4 ) 4 ] 4À and [Cd(C 2 O 4 ) 4 ] 6À anions.…”