K W Hipps - Polymorphic, Porous, and Host–Guest Nanostructures Directed by Monolayer–Substrate Interactions: Epitaxial Self-Assembly Study of Cyclic Trinuclear Au(I) Complexes on HOPG at the Solution–Solid Interface

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  Chilukuri, Bhaskar, McDougald, Roy N., Ghimire, Mukunda M.,   Nesterov, Vladimir N., Mazur, Ursula, Omary, Mohammad A., Hipps,   K. W. The Journal of Physical Chemistry C  2015 119 (44) 24844-24858

  Abstract: Synthesis, crystallographic   characterization, and molecular self-assembly of two novel   cyclotrimeric gold(I) complexes, Au3[3,5-(COOEt)2Pz]3 (Au3Pz3)   and Au3[(n-Pr–O)C═N(Me)]3 (Au3Cb3) was studied. Single crystal   X-ray crystallography data reveal that both gold(I) complexes   have one-dimensional stacking patterns caused by intermolecular   Au(I)···Au(I) aurophilic interactions. The Au3Pz3 trimer units   stack with two alternate and symmetrical Au(I)···Au(I)   interactions while the Au3Cb3 units have three alternating and   nonsymmetrical Au(I)···Au(I) interactions. Molecular   self-assembly of the gold(I) complexes on the   1-phenyloctane/highly ordered pyrolytic graphite (HOPG) (0001)   solution–solid interface is studied with scanning tunneling   microscopy (STM). The gold(I) cyclotrimers form epitaxial   nanostructures on the HOPG surface. At a concentration of ∼1 ×   10–4 M, Au3Pz3 complexes exhibit a single morphology, while   Au3Cb3 complexes exhibit polymorphology. Two polymorphs, one   nonporous and the other porous, are observed at 22.0 ± 2.0 °C for   Au3Cb3 complexes. A nonporous, low-surface-density (0.82   molecules/nm2) Au3Cb3 nanostructure forms first and then   transforms into a high-density (1.43 molecules/nm2) porous   nanostructure. This is the first time any porous surface   nanostructure is reported for an organometallic system. The   porous structure is thought to be stabilized by a combination of   hydrogen bonding and monolayer–substrate interactions. These   pores are utilized to incorporate pyrene into the film, rendering   this the first organometallic host–guest system imaged at the   solid–solution interface. Molecular and periodic density   functional theory (DFT) calculations shed light on the   two-dimensional topography and polymorphic self-assembly revealed   by STM; these calculations suggest significant electronic   hybridization of the Au3 trimer orbitals and HOPG. The   multiple-technique approach used herein provides insights   concerning molecule–substrate and molecule–molecule interactions.

  Address (URL): http://dx.doi.org/10.1021/acs.jpcc.5b08171