Conductive Self-Assembled Monolayers of Paramagnetic {Co II Co 4 III } and { Co 4 II Co 2 III } Coordination Clusters on Gold Surfaces.

Two polynuclear cobalt(II,III) complexes, [Co-5(N-3)(4)(N-n-bda)(4)(bza center dot SMe)(2)] (1) and [Co-6(N-3)(4)(N-n-bda)(2)(bza center dot SMe)(5)(MeOH)(4)]Cl (2), where Hbza center dot SMe = 4-(methylthio)benzoic acid and N-n-H(2)bda = N-n-butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound 1 exhibits an unusual, approximately C-2-symmetric {Co(II)Co4III} core of two isosceles Co-3 triangles with perpendicularly oriented planes, sharing a central, high-spin Co-II ion residing in a distorted tetrahedral coordination environment. This central Co-II ion is connected to four outer, octahedrally coordinated low-spin Co-III ions via oxo bridges. Compound 2 comprises a semi-circular {Co4IICo2III} motif of four non-interacting high-spin Co-II and two low-spin Co-III centers in octahedral coordination environments. Self-assembled monolayers (SAMs) of 1 and 2 were physisorbed on template-stripped gold surfaces contacted by an eutectic gallium-indium (EGaIn) tip. The acquired current density-voltage (I-V) data revealed that the cobalt-based SAMs are more electrically robust than those of the previously reported dinuclear {Cu(II)Ln(III)} complexes with Ln = Gd, Tb, Dy, or Y (Schmitz et al., 2018a). In addition, between 170 and 220 degrees C, the neutral, mixed-valence compound 1 undergoes a redox modification, yielding a {Co-5}-based coordination cluster (1-A) with five non-interacting, high-spin octahedral Co-II centers as indicated by SQUID magnetometry analysis in combination with X-ray photoelectron spectroscopy and infrared spectroscopy. Solvothermal treatment of 1 results in a high-nuclearity coordination cluster, [Co-10(N-3)(2)(N-n-bda)(6)(bza center dot SMe)(6)] (3), containing 10 virtually non-interacting high-spin Co-II centers.