Bernhard Bugenhagen

Toward Tailored All-Spin Molecular Devices

Molecular based spintronic devices offer great potential for future energy-efficient information technology as they combine ultimately small size, high-speed operation, and low-power consumption. Recent developments in combining atom-by-atom assembly with spin-sensitive imaging and characterization at the atomic level have led to a first prototype of an all-spin atomic-scale logic device, but the very low working temperature limits its application. Here, we show that a more stable spintronic device could be achieved using tailored Co-Salophene based molecular building blocks, combined with in situ electrospray deposition under ultrahigh vacuum conditions as well as control of the surface-confined molecular assembly at the nanometer scale. In particular, we describe the tools to build a molecular, strongly bonded device structure from paramagnetic molecular building blocks including spin-wires, gates, and tails. Such molecular device concepts offer the advantage of inherent parallel fabrication based on molecular self-assembly as well as an order of magnitude higher operation temperatures due to enhanced energy scales of covalent through-bond linkage of basic molecular units compared to substrate-mediated coupling schemes employing indirect exchange coupling between individual adsorbed magnetic atoms on surfaces.

On-Surface Oligomerization of Self-Terminating Molecular Chains for the Design of Spintronic Devices

Molecular spintronics is currently attracting a lot of attention due to its great advantages over traditional electronics. A variety of self-assembled molecule-based devices are under development, but studies regarding the reliability of the growth process remain rare. Here, we present a method to control the length of molecular spintronic chains and to make their terminations chemically inert, thereby suppressing uncontrolled coupling to surface defects. The temperature evolution of chain formation was followed by X-ray photoelectron spectroscopy to determine optimal growth conditions. The final structures of the chains were then studied, using scanning tunneling microscopy, as a function of oligomerization conditions. We find that short chains are readily synthesized with high yields and that long chains, even exceeding 70mers, can be realized under optimized growth parameters, albeit with reduced yields.

Ethyl (E)-3-(anthracen-9-yl)prop-2-enoate

In the asymmetric unit of the title compound, C19H16O2, there are two symmetry-independent molecules (A and B) that differ in the conformation of the ester ethoxy group. In the crystal, the molecules form inversion dimers via pairs of C—H⋯O interactions. Within the dimers, the anthracenyl units have interplanar distances of 0.528 (2) and 0.479 (2) Å for dimers of molecules A and B, respectively. Another short C—H⋯O contact between symmetry-independent dimers links them into columns parallel to [10-1]. These columns are arranged into (111) layers and there are π–π stacking interactions [centroid–centroid distances = 3.6446 (15) and 3.6531 (15) Å] between the anthracenyl units from the neighbouring columns. In addition, there are C—H⋯π interactions between the anthracenyl unit of dimers A and dimers B within the same column.

Cholest-5-en-3β-yl 3-(4-eth-oxy-phen-yl)prop-2-enoate.

In the asymmetric unit of the title compound, C38H56O3, there are two symmetry-independent molecules that differ in the rotation angle along the C—O bond between the 3-(4-ethoxyphenyl)prop-2-enoate and cholest-5-en-3β-yl groups by 169.3 (3)°. In both molecules, steroid ring B adopts a half-chair conformation, rings A and C adopt a chair conformation and ring D exists in an envelope form. The two symmetry-independent molecules pack in the crystal into separate layers parallel to (-102) with their long axis parallel to the [201] direction. Short intermolecular C—H⋯O and C—H⋯π contacts are observed.

Preparation of 3-(9-Anthryl)acrylates and 9-Aroylethenylanthracenes as Pi-Extended Anthracenes and Their Diels–Alder Type Adducts with Electron-Poor Dienophiles

ABSTRACT (E)-3-(9-Anthryl)acrylates and (E)-9-aroylethenylanthracenes have been prepared by solventless Wittig olefination with conjugated phosphoranes. The (E)-3-(9-anthryl)acrylates were brominated to give (E)-3[10-{9-bromoanthryl}]acrylates, which could be subjected to Suzuki reactions with arylboronic acids to produce (E)-3-[10-{9-arylanthryl}]acrylates as pi-extended systems. The compounds thus prepared were subjected to Diels–Alder reactions, partly under solventless conditions.

Crystal structure of (1Z,2E)-cinnamaldehyde oxime.

The title compound, C9H9NO, crystallized with two independent molecules (A and B) in the asymmetric unit. The conformation of the two molecules differs slightly with the phenyl ring in molecule A, forming a dihedral angle of 15.38 (12)° with the oxime group (O—N=C), compared to the corresponding angle of 26.29 (11)° in molecule B. In the crystal, the A and B molecules are linked head-to-head by O—H⋯N hydrogen bonds, forming –A–B–A–B– zigzag chains along [010]. Within the chains and between neighbouring chains there are C—H⋯π interactions present, forming a three-dimensional structure.

Crystal structure of bis­(μ2-4-tert-butyl-2-formyl­phenolato)-1:2κ3O1,O2:O1;3:4κ3O1,O2:O1-bis­(4-tert-butyl-2-formyl­phenolato)-2κ2O1,O2;4κ2O1,O2-di-μ3-methoxido-1:2:3κ3O;1:3:4κ3O-di-μ2-methoxido-1:4κ2O;2:3κ2O-tetra­copper(II)

The dinuclear title compound crystallizes as a dimer forming a tetranuclear copper(II) complex, [Cu4(CH3O)4(C11H13O2)4], in the solid state. In this complex, all CuII atoms have a square-pyramidal coordination sphere, with long axial and short basal Cu—O distances.

Crystal structure of cholest-5-en-3β-yl 3-(2,4-dimeth-oxy-3-methyl-phen-yl)prop-2-enoate.

In the title compound, C39H58O4, the steroid rings A and C adopt a chair conformation, while ring B adopts a half-chair conformation, and ring D has an envelope conformation, with the methyl-substituted C atom as the flap. In the crystal, molecules pack within layers parallel to (100), with their long axis parallel to the [101] direction. Adjacent layers are linked via C—H⋯O hydrogen bonds and C—H⋯π interactions, forming a three-dimensional framework.

2,5-Di­meth­oxy­benzo­nitrile

In the title molecule, C9H9NO2, the non-H atoms are essentially coplanar with a maximum deviation of 0.027 (2) Å for the C atom of one of the methyl groups. In the crystal, the molecules are arranged into centrosymmetric pairs via pairs of C—H⋯O and C—H⋯N interactions whereas π–π stacking interactions between the benzene rings [centroid–centroid distance 3.91001 (15) Å] organize them into polymeric strands propagating along the a-axis direction. There is a step of 0.644 (2) Å between the two planar parts of the centrosymmetric pair. In neighboring strands related by the n-glide operation, the aromatic rings are tilted by 29.08 (2)°.

2-(Prop-2-enyloxy)benzamide.

In the title molecule, C10H11NO2, the benzene ring forms dihedral angles of 33.15 (2) and 6.20 (2)° with the mean planes of the amide and propenoxy groups, respectively. The amide –NH2 group is oriented toward the propenoxy substituent and forms a weak intramolecular N—H⋯O hydrogen bond to the propenoxy O atom. The conformation of the propenoxy group at the Csp 2—Csp 3 and Csp 3—O bonds is synperiplanar and antiperiplanar, respectively. In the crystal, N—H⋯O hydrogen bonds involving the amide groups generate C(4) and R 2 3(7) motifs that organize the molecules into tapes along the a-axis direction. There are C—H⋯π interactions between the propenoxy –CH2 group and the aromatic system of neighboring molecules within the tape. The mean planes of the aromatic ring and the propenoxy group belonging to molecules located on opposite sites of the tape form an angle of 83.16 (2)°.