Abstract
Two polynuclear cobalt(II,III) complexes, [Co(5)(N(3))(4)(N-n-bda)(4)(bza·SMe)(2)] (1) and [Co(6)(N(3))(4)(N-n-bda)(2)(bza·SMe)(5)(MeOH)(4)]Cl (2), where Hbza·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 { Co4II Co2III } 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°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·SMe)(6)] (3), containing 10 virtually non-interacting high-spin Co(II) centers.