Abstract
Two polynuclear cobalt(II,III) complexes, [Co5(N3)4(N-n-bda)4(bza·SMe)2] (1) and [Co6(N3)4(N-n-bda)2(bza·SMe)5(MeOH)4]Cl (2), where Hbza·SMe = 4-(methylthio)benzoic acid and N-n-H2bda = N-n-butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound 1 exhibits an unusual, approximately C2-symmetric {CoII} core of two isosceles Co3 triangles with perpendicularly oriented planes, sharing a central, high-spin CoII ion residing in a distorted tetrahedral coordination environment. This central CoII ion is connected to four outer, octahedrally coordinated low-spin CoIII ions via oxo bridges. Compound 2 comprises a semi-circular {} motif of four non-interacting high-spin CoII and two low-spin CoIII 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 {CuIILnIII} 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 {Co5}-based coordination cluster (1-A) with five non-interacting, high-spin octahedral CoII 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, [Co10(N3)2(N-n-bda)6(bza·SMe)6] (3), containing 10 virtually non-interacting high-spin CoII centers.
Highlights
IntroductionThe so-called “quantum limit” (sub-10-nm regime) valid
The implementation of metal coordination complexes with specific paramagnetic and/or redox properties as single molecules or as constituents of two-dimensional molecular monolayers (Yao et al, 2019) into computer memory cells (Linnenberg et al, 2018) is a promising way to keep the miniaturization and sustainability of electronic components from colliding withSelf-Assembled Monolayers of Cobalt Complexes on GoldGRAPHICAL ABSTRACT | The synthesis, structure, magnetochemistry and adsorption behavior of several new cobalt coordination clusters on gold surfaces are reported.the so-called “quantum limit” valid
Based on our ongoing interest in investigating the largearea charge transport properties of moisture-stable polynuclear transition metal complexes, we describe the synthesis, structure, and magnetochemistry of novel mixed-valent CoII/III and mono-valent CoII coordination clusters and assess their abilities to exhibit reproducible electrical conductivity features when deposited on a metallic substrate
Summary
The so-called “quantum limit” (sub-10-nm regime) valid At both these levels of molecule–surface interfaces, preservation of the main molecular characteristics (Mitcov et al, 2019) as identified in the bulk state, and avoidance of the agglomerative behavior of coordination compounds after their immobilization on solid support constitute important milestones in the controlled (micro-)spectroscopic addressing of the tunnel junction structures of molecule–electrode hybrid devices. The eventual step to practical devices (Sun et al, 2014) mandates an in-depth understanding of the adsorption, autonomous selforganization, electron charge-/spin-transport characteristics (AlOwaedi et al, 2017; Bu et al, 2018) and switching mechanisms of mono- and polynuclear complexes of transition metals (Higgins and Nichols, 2018), lanthanides (Dreiser, 2015), and their mixedmetal derivatives (Schmitz et al, 2018a) on conductive and semi-conductive surfaces (Cornia et al, 2011). It is noteworthy that metal complexes derivatized by thiane functionalities as, for example, mononuclear copper(II) pyridyl–alcohol complexes are capable of featuring close intermolecular S···S contacts in the crystal lattice (Schmitz et al, 2019)
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