7 research outputs found
Structural Evolution from 0D Units to 3D Frameworks in Pb Oxyhalides: Unexpected Strongly Corrugated Layers in Pb<sub>7</sub>O<sub>6</sub>Br<sub>2</sub>
Novel Pb<sub>7</sub>O<sub>6</sub>Br<sub>2</sub> (<b>1</b>) lead oxybromide was prepared from
Pb oxybromide melt by the “rapid quenching” route. Bonding
scheme, thermal expansion, and structural properties were studied.
The structural features of this unexpectedly complex phase are described
on the basis of lone electron pair stereochemical activity and Pb–Br
versus Pb–O bonding scheme. The structure of <b>1</b> contains a number of cavities, which can be assigned to the self-containments
of the lone electron pairs on Pb<sup>2+</sup> cations. “Empty”
□Pb<sub>4</sub> chains are observed in between of the folding
sides of the adjacent strongly corrugated oxocentered [Pb<sub>7</sub>O<sub>6</sub>]<sup>2+</sup> layers. Highly isotropic thermal expansion
of <b>1</b> appeared to be unexpected. The possible explanations
of such a behavior in <b>1</b> are given. The structure of <b>1</b> is an interesting example of tetrahedral framework with
mixed chemical bonding and is the densest known among Pb oxyhalides
with the density of 18.4 tetrahedra/1000 Å<sup>3</sup>. Current
study shows that oxocentered layers derivatives from α-PbO can
be very flexible and form rather dense three-dimensional structural
topologies. The properties and structure are compared to other phases
crystallizing in the anhydrous PbO–Pb<i>X</i><sub>2</sub> (X = F, Cl, Br, I) systems, illustrate the complexity of
lead oxyhalides, and reveal new and general pathways for the targeted
synthesis of new phases with the Pb–O units of desired dimensionality.
The indirect gap value of ∼2.04 eV obtained from generalized
gradient approximation calculations demonstrates potentially good
photocatalytic properties of <b>1</b>