Manipulating Ligand Density at the Surface of Polyoxovanadate-Alkoxide Clusters

We present the post-synthetic modification of a polyoxovanadate-alkoxide (POV-alkoxide) cluster via the reactivity of its cationic form, [V6O7(OCH3)12]1+, with water. This result indicates that cluster oxidation increases the lability of bridging methoxide ligands, affording a ligand exchange reaction that serves to compensate for the increased charge of the cluster core. This synthetic advance affords the isolation of a series of POV-alkoxide clusters with varying degrees of μ2–O2– ligands incorporated at the surface, namely, [V6O8(OCH3)11], [V6O9(OCH3)10], and [V6O10(OCH3)9]. Characterization of the POV-alkoxide clusters is described; changes in the infrared and electronic absorption spectra are consistent with the oxidation of the cluster core. We also examine the consequences of ligand substitution on the redox properties of the series of POV-alkoxide clusters via cyclic voltammetry; decreased alkoxide ligand density translates to a cathodic shift of analogous redox events. Ligand substitution also increases comproportionation constants of the Lindqvist core, indicating electron exchange between vanadium centers is promoted in structures with greater numbers of μ2–O2– ligands.

Manipulating Ligand Density at the Surface of Polyoxovanadate-Alkoxide Clusters Thompson V. Marinho, a ‡ Eric Schreiber, a ‡ Rachel E. Garwick, William W. Brennessel, a and Ellen M. Matson a * a Department of Chemistry, University of Rochester, Rochester, New York 14627 ‡ Authors contributed equally to this work *Corresponding author email: matson@chem.rochester.edu

Supporting Information Table of Contents
Table S1.Crystallographic

3 Figure
Figure S1.H NMR spectrum of the crude reaction performed in a J-Young tube of V6O7 1+ and 150 equiv of D2O collected in CD3CN at 21 o C after 30 min; inset shows formation of methanol following addition of D2O (top).H NMR spectrum of the starting material, V6O7 1+ , collected in CD3CN at 21 o C (bottom).

Figure S2 .
Figure S2.H NMR spectra of crude reaction of [V6O7(OCH3)12] 0 and 150 equiv H2O.Time points taken immediately after addition (green), 13 hours after addition of water (teal), and one week after addition of water (purple, bottom).(*) signals indicate formation of V6O8 in the bottom spectrum, suggesting conversion of the neutral POV-alkoxide cluster to V6O8 is possible after prolonged exposure to water.

Figure S7 .
Figure S7.From top to bottom, infrared spectra of V6O7 (black), V6O8 (green), V6O9 (purple), and V6O10 (red).Inset shows a magnification of the region between 500 and 1100 cm -1 where pertinent bands of the cluster core are observed.

Figure S14 .
Figure S14.ESI-MS(-)ve of reaction of V6O8 1+ and H2O; Sample A contains portion of product that is soluble in Et2O (top, both full spectrum and cluster-containing region shown for clarity), while Sample B contains portion of product that is insoluble in Et2O (bottom, both full spectrum and cluster-containing region are shown for clarity).As evidenced from this data, a mixture of products, V6O9 (minor), V6O10, and V6O11 (minor), is formed.Only V6O10 could be isolated in meaningful yield.

Table S1 .
Crystallographic parameters for molecular structures of V6O9 and V6O10.

Table S2 .
Bond valence sum calculations for V6O9 based on X-Ray crystallographic data collected at 100 K. Table reflects the results of BVS calculations using V-O valence parameters (r0) for different oxidation states of vanadium.
1 H NMR spectrum of [V6O7(OC2H5)12] 1+ with H2O added collected in CD3CN at 21 o C. Spectrum is consistent with peaks of the starting material.