AUTHOR=Schmitz Sebastian , Qiu Xinkai , Glöß Maria , van Leusen Jan , Izarova Natalya V. , Nadeem Muhammad Arif , Griebel Jan , Chiechi Ryan C. , Kögerler Paul , Monakhov Kirill Yu. 

TITLE=Conductive Self-Assembled Monolayers of Paramagnetic {CoIICo4III} and {Co4IICo2III} Coordination Clusters on Gold Surfaces

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00681

DOI=10.3389/fchem.2019.00681

ISSN=2296-2646

ABSTRACT=<p>Two polynuclear cobalt(II,III) complexes, [Co<sub>5</sub>(N<sub>3</sub>)<sub>4</sub>(<italic>N</italic>-<italic>n</italic>-bda)<sub>4</sub>(bza·SMe)<sub>2</sub>] (<bold>1</bold>) and [Co<sub>6</sub>(N<sub>3</sub>)<sub>4</sub>(<italic>N</italic>-<italic>n</italic>-bda)<sub>2</sub>(bza·SMe)<sub>5</sub>(MeOH)<sub>4</sub>]Cl (<bold>2</bold>), where Hbza·SMe = 4-(methylthio)benzoic acid and <italic>N</italic>-<italic>n</italic>-H<sub>2</sub>bda = <italic>N</italic>-<italic>n</italic>-butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound <bold>1</bold> exhibits an unusual, approximately <italic>C</italic><sub>2</sub>-symmetric {Co<sup>II</sup><inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>Co</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mtext>III</mml:mtext></mml:mrow></mml:msubsup></mml:math></inline-formula>} core of two isosceles Co<sub>3</sub> triangles with perpendicularly oriented planes, sharing a central, high-spin Co<sup>II</sup> ion residing in a distorted tetrahedral coordination environment. This central Co<sup>II</sup> ion is connected to four outer, octahedrally coordinated low-spin Co<sup>III</sup> ions <italic>via</italic> oxo bridges. Compound <bold>2</bold> comprises a semi-circular {<inline-formula><mml:math id="M5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>Co</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mtext>II</mml:mtext></mml:mrow></mml:msubsup></mml:math></inline-formula><inline-formula><mml:math id="M6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>Co</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mtext>III</mml:mtext></mml:mrow></mml:msubsup></mml:math></inline-formula>} motif of four non-interacting high-spin Co<sup>II</sup> and two low-spin Co<sup>III</sup> centers in octahedral coordination environments. Self-assembled monolayers (SAMs) of <bold>1</bold> and <bold>2</bold> were physisorbed on template-stripped gold surfaces contacted by an eutectic gallium-indium (EGaIn) tip. The acquired current density-voltage (<italic>I-V</italic>) data revealed that the cobalt-based SAMs are more electrically robust than those of the previously reported dinuclear {Cu<sup>II</sup>Ln<sup>III</sup>} complexes with Ln = Gd, Tb, Dy, or Y (Schmitz et al., <xref ref-type="bibr" rid="B29">2018a</xref>). In addition, between 170 and 220°C, the neutral, mixed-valence compound <bold>1</bold> undergoes a redox modification, yielding a {Co<sub>5</sub>}-based coordination cluster (<bold>1-A</bold>) with five non-interacting, high-spin octahedral Co<sup>II</sup> centers as indicated by SQUID magnetometry analysis in combination with X-ray photoelectron spectroscopy and infrared spectroscopy. Solvothermal treatment of <bold>1</bold> results in a high-nuclearity coordination cluster, [Co<sub>10</sub>(N<sub>3</sub>)<sub>2</sub>(<italic>N</italic>-<italic>n</italic>-bda)<sub>6</sub>(bza·SMe)<sub>6</sub>] (<bold>3</bold>), containing 10 virtually non-interacting high-spin Co<sup>II</sup> centers.</p>