Chemical design of single molecule electronic components and quasi-1D chains
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Abstract
A series of heterobimetallic lantern complexes of the form [PtFe(SOCR)4(pyX)] (R = Me, X = H (1), X = NH2 (2), X = SMe (3); R = Ph, X = H (4), X = NH2 (5), X = SMe (6)) have been synthesized and characterized, including 57Fe Mössbauer spectroscopy. The synthesis of the new complexes in this family (1, 4, 5, 6) are reported along with a detailed structure-property comparison across the entire series. Substitutions made on the thiocarboxylate backbone (R) and the pyridine axial ligand (X) significantly affect the quadrupole splitting (ΔEQ) in the Mössbauer measurements. The quasi-1D chain [PtCo(SAc)4(4,4’-bipy)]∞ (7) has been synthesized via bottom-up assembly of individual lantern units coupled by 4,4’-bipyridine bridging ligands. Synthesis and characterization, including magnetic studies are reported. A new series of heterobimetallic lantern complexes [PtM(tba)4(pySMe)] (M = Mn (10), Fe (6), Co (11), Ni (12), Zn (13)) and homobimetallic lantern complexes [Cu2(OAc)4(pySMe)2] (14) and [Co2(esp)2(pySMe)2] (15) have been synthesized and characterized. These complexes were utilized to study the incorporation of coordination complexes into metal-molecule-metal junctions via the Scanning Tunneling Microscope Break Junction (STMBJ) technique. Single molecule conductance measurements reveal that intramolecular metal-ligand bonding is vulnerable to rearrangement on Au electrodes and competition from Au-ligand binding is consistent with empirical hard-soft acid-base principles. Single molecule conductance measurements in the presence of [KM(CN)2] (M = Au, Ag) are reported, which produce numerous conductance features ranging from 10-1 – 10-6 G0 at distinct junction elongations. Some junction extensions are longer than predicted for a [(NC)Au(CN)]1- molecular bridge between Au electrodes, suggesting rearrangement and in situ formation of molecular wires. Quantum interference effects between σ and π molecular orbitals have been identified in ~ 4 Å pyrazine-based molecules, bridging source and drain electrodes. Destructive interference effects were modulated via external pH control, as demonstrated by single molecule conductance measurements and electronic transport calculations.
Description
2023