Element-Selective Molecular Charge Transport Characteristics of Binuclear Copper(II)-Lanthanide(III) Complexes

A series of isostructural dinuclear 3d-4f complexes, isolated as [CuLn(L·SMe)2(OOCMe)2(NO3)]·xMeOH (Ln = Gd 1, Tb 2, Dy 3, and Y 4; x = 0.75–1) and comprising one acetate and two thioether-Schiff base (L·SMe–) bridging ligands based on 4-(methylthio)aniline and 2-hydroxy-3-methoxybenzaldehyde (HL·SMe = C15H15NO2S), was synthesized and fully characterized. The magnetic properties of the charge-neutral {CuLn} complexes are dominated by ferromagnetic CuII–LnIII exchange interactions. Large-area electron transport studies reveal that the average conductivity of robust, self-assembled {CuLn} monolayers on a gold substrate is significantly lower than that of common alkanethiolates. Theoretical calculations of transmission spectra of individual complexes 1 and 4 embedded between two metallic electrodes show that the molecular current–voltage (I–V) characteristics are strongly influenced by electron transport through the Cu centers and thus fully independent of the lanthanide ion, in excellent agreement with the experimental I–V data for 1–4. The β-polarized transmission indicated by calculations of 1 and 4 points out their potential as spin filters. In addition, the reactivity of the title compound 1 with CuII in a square-pyramidal coordination environment toward methanolate and azide was examined, resulting in the formation of a linear trinuclear complex, [Cu2Na(L·SMe)4]NO3·3MeOH (5), characterized by antiferromagnetic exchange interactions between the two copper ions

Synthesis, directed self-assembly, IRRAS and electrical properties studied on amphiphilic and zwitterionic Janus Gold nanoparticles

Gold nanoparticles (AuNPs) have gained significant scientific and technological importance due to their facile synthesis, their exceptional stability, their versatile surface chemistry and their tunable optical properties. By symmetry-breaking syntheses, Janus functionality can be imparted to AuNPs, which thereby present different chemical and physical properties on their opposite ends. Janus AuNPs represent a unique class of nanomaterials as they are suited, e.g., as Pickering type surfactants, as building blocks for functional self-assembled superstructures and as building blocks for nanoelectronic devices exhibiting asymmetric, diode-like current characteristics. A crucial step to realize these applications is to validate the asymmetric functionalization of the Janus AuNPs unequivocally. For this purpose, the respective ligands need to be detected selectively, which despite the development of groundbreaking instruments and methods of investigation still remains challenging as a confined area of the particles has to be analyzed. Therefore, this work focuses on synthesizing amphiphilic and zwitterionic Janus AuNPs, on validating their Janus character by IRRAS and on evaluating their electrical properties in order to assess their applicability in novel, optoelectronic devices.Amphiphilic and zwitterionic Janus AuNPs in the size range of 12 -15 nm were obtained by two-phase ligand exchange reactions at liquid/liquid and solid/liquid interfaces, respectively. Samples of Janus AuNPs for IRRAS and electrical measurements were prepared by applying directed self-assembly (DSA). In this way, amphiphilic AuNPs were directionally deposited on polar and non-polar gold substrates and zwitterionic AuNPs on gold substrates functionalized with a negatively or positively charged molecular monolayer. By fine-tuning the parameters influencing the DSA process, monolayers of Janus AuNPs exhibiting a specific orientation over macroscopic areas were obtained. During the IRRAS measurements of these samples, one of the two ligands of the Janus AuNPs pointed towards the substrate and was shielded from the IR radiation by the AuNPs’ core, while the other one was selectively detected and analyzed. Thus, the Janus character of the synthesized amphiphilic and zwitterionic AuNPs presenting diameters larger than 10 nm was directly proven, which up to now had not been accomplished. The electrical properties of the directionally deposited Janus AuNPs were investigated using a homemade setup allowing to perform locally resolved electrical measurements at ambient conditions

Directed Self-Assembly and Infrared Reflection Absorption Spectroscopy Analysis of Amphiphilic and Zwitterionic Janus Gold Nanoparticles

Here, we report an approach to use infrared reflection absorption spectroscopy (IRRAS) for the unambiguous proof of the presence as well as the spatial distribution of organic ligands on the Janus gold nanoparticle (AuNP) surface. For this purpose we synthesized amphiphilic and zwitterionic Janus AuNPs and immobilized these on pretreated gold surfaces by directed self-assembly, exploiting hydrophilic/hydrophobic or electrostatic interactions, respectively. Thus, we obtained macroscopic two-dimensional arrays of Janus AuNPs exhibiting a specific orientation. These arrays were investigated by IRRAS, and the obtained spectra revealed only peaks of the ligands facing the IR beam, while the ligands facing the gold substrate were not detected due to reflection of the IR beam on the AuNP cores. Thus, we describe a straightforward spectroscopic procedure to prove the Janus character of zwitterionic and amphiphilic AuNPs in the size range of 10–15 nm

Probing Frontier Orbital Energies of {Co 9 (P 2 W 15 ) 3 } Polyoxometalate Clusters at Molecule–Metal and Molecule–Water Interfaces

Functionalization of polyoxotungstates with organoarsonate coligands enabling surface decoration was explored for the triangular cluster architectures of the composition [CoII9(H2O)6(OH)3(p-RC6H4AsVO3)2(α-PV2WVI15O56)3]25– ({Co9(P2W15)3}, R = H or NH2), isolated as Na25[Co9(OH)3(H2O)6(C6H5AsO3)2(P2W15O56)3]·86H2O (Na-1; triclinic, P1̅, a = 25.8088(3) Å, b = 25.8336(3) Å, c = 27.1598(3) Å, α = 78.1282(11)°, β = 61.7276(14)°, γ = 60.6220(14)°, V = 13888.9(3) Å3, Z = 2) and Na25[Co9(OH)3(H2O)6(H2NC6H4AsO3)2(P2W15O56)3]·86H2O (Na-2; triclinic, P1̅, a = 14.2262(2) Å, b = 24.8597(4) Å, c = 37.9388(4) Å, α = 81.9672(10)°, β = 87.8161(10)°, γ = 76.5409(12)°, V = 12920.6(3) Å3, Z = 2). The axially oriented para-aminophenyl groups in 2 facilitate the formation of self-assembled monolayers on gold surfaces and thus provide a viable molecular platform for charge transport studies of magnetically functionalized polyoxometalates. The title systems were isolated and characterized in the solid state, in aqueous solutions, and on metal surfaces. Using conducting tip atomic force microscopy, the energies of {Co9(P2W15)3} frontier molecular orbitals in the surface-bound state were found to directly correlate with cyclic voltammetry data in aqueous solution

Triangular {Ni3} coordination cluster with a ferromagnetically coupled metal-ligand core

The coordination characteristics of a tridentate, π-conjugated Schiff base (HL·SMe) combined with 4-(methylthio)benzoic acid (Hbza·SMe) were explored in methanol solution. A two-step aerobic process involving the precursor NiCl2·6H2O afforded the trinuclear coordination compound [NiII3(L·SMe)4(bza·SMe)(MeOH)2]Cl0.5(CH3O)0.5·5.5MeOH·H2O (1), while the precursor Ni(ClO4)2·6H2O resulted in [NiII3(L·SMe)4(bza·SMe)(MeOH)2](ClO4)0.75(CH3O)0.25·1.5MeOH·0.75H2O (2); in both cases the thioether-containing ligands are key to isolation of crystalline products. Their solvent-free cationic motif [Ni3(L·SMe)4(bza·SMe)]+, supported by two different types of monodeprotonated chelate ligands, has been studied by electrospray ionization mass spectrometry. 1 and 2 crystallize in the triclinic space group and monoclinic space group Cc, respectively, and feature a hitherto not observed triangular metal-ligand skeleton that is characterized by predominantly ferromagnetic exchange coupling between Ni(II) ions. Proof-of-concept infrared reflection–absorption spectroscopy measurements of 1 deposited on a gold substrate indicate that this moisture-stable compound retains its main structural features upon adsorption on the metal surface, which enables subsequent studies of catalytic properties of 1 on a solid support

Probing Frontier Orbital Energies of {Co 9 (P 2 W 15 ) 3 } Polyoxometalate Clusters at Molecule–Metal and Molecule–Water Interfaces

Full paper with figures and supporting informationInternational audienceFunctionalization of polyoxotungstates with organoarsonate co-ligands enabling surface decoration was explored for the triangular cluster architectures of the composition [CoII9(H2O)6(OH)3(p-RC6H4AsVO3)2({\alpha}-PV2WVI15O56)3]25-({Co9(P2W15)3}, R = H or NH2), isolated as Na25[Co9(OH)3(H2O)6(C6H5AsO3)2(P2W15O56)3]86H2O (Na-1) and Na25[Co9(OH)3(H2O)6(H2NC6H4AsO3)2(P2W15O56)3]86H2O (Na-2). The axially oriented para-aminophenyl groups in 2 facilitate the formation of self-assembled monolayers on gold surfaces, and thus provide a viable molecular platform for charge transport studies of magnetically functionalized polyoxometalates. The title systems were isolated and characterized in the solid state and in aqueous solutions, and on metal surfaces. Using conducting tip atomic force microscopy (C-AFM), the energies of {Co9(P2W15)3} frontier molecular orbitals in the surface-bound state were found to directly correlate with cyclic voltammetry data in aqueous solution

Differential Adsorption of Gold Nanoparticles to Gold/Palladium and Platinum Surfaces

Integration of molecule-capped gold nanoparticles (AuNP) into nanoelectronic devices requires detailed knowledge about the AuNP–electrode interface. Here, we report the pH-dependent adsorption of amine or carboxylic acid-terminated gold nanoparticles on platinum or gold/palladium (30% Pd) alloy, respectively. We synthesized amine-terminated AuNP, applying a new solid phase supported approach, as well as AuNP exhibiting carboxylic acid as terminal groups. The pH-induced agglomeration of the synthesized AuNP was investigated by UV–vis, DLS, and ζ-potential measurements. Depending on the pH and the ionic strength of the AuNP solution a preferential adsorption on the different metals occurred. Thereby, we demonstrate that by choosing the appropriate functional group and adjusting the pH as well as the ionic strength a directed binding can be achieved, which is an essential prerequisite for applications of these particles in nanoelectronics. These findings will pave the way for a controlled designing of the interface between molecule-capped AuNP and metallic electrodes for applications in nanoelectronics

Probing Frontier Orbital Energies of {Co9(P2W15)3} Polyoxometalate Clusters at Molecule-Metal and Molecule-Water Interfaces.

Functionalization of polyoxotungstates with organoarsonate coligands enabling surface decoration was explored for the triangular cluster architectures of the composition [CoII9(H2O)6(OH)3(p-RC6H4AsVO3)2(α-PV2WVI15O56)3]25- ({Co9(P2W15)3}, R = H or NH2), isolated as Na25[Co9(OH)3(H2O)6(C6H5AsO3)2(P2W15O56)3]·86H2O (Na-1; triclinic, P1̅, a = 25.8088(3) Å, b = 25.8336(3) Å, c = 27.1598(3) Å, α = 78.1282(11)°, β = 61.7276(14)°, γ = 60.6220(14)°, V = 13888.9(3) Å3, Z = 2) and Na25[Co9(OH)3(H2O)6(H2NC6H4AsO3)2(P2W15O56)3]·86H2O (Na-2; triclinic, P1̅, a = 14.2262(2) Å, b = 24.8597(4) Å, c = 37.9388(4) Å, α = 81.9672(10)°, β = 87.8161(10)°, γ = 76.5409(12)°, V = 12920.6(3) Å3, Z = 2). The axially oriented para-aminophenyl groups in 2 facilitate the formation of self-assembled monolayers on gold surfaces and thus provide a viable molecular platform for charge transport studies of magnetically functionalized polyoxometalates. The title systems were isolated and characterized in the solid state, in aqueous solutions, and on metal surfaces. Using conducting tip atomic force microscopy, the energies of {Co9(P2W15)3} frontier molecular orbitals in the surface-bound state were found to directly correlate with cyclic voltammetry data in aqueous solution