Interface-engineered templates for molecular spin memory devices.

The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices, opening avenues for developing multifunctional molecular spintronics. Such ideas have been researched extensively, using single-molecule magnets and molecules with a metal ion or nitrogen vacancy as localized spin-carrying centres for storage and for realizing logic operations. However, the electronic coupling between the spin centres of these molecules is rather weak, which makes construction of quantum memory registers a challenging task. In this regard, delocalized carbon-based radical species with unpaired spin, such as phenalenyl, have shown promise. These phenalenyl moieties, which can be regarded as graphene fragments, are formed by the fusion of three benzene rings and belong to the class of open-shell systems. The spin structure of these molecules responds to external stimuli (such as light, and electric and magnetic fields), which provides novel schemes for performing spin memory and logic operations. Here we construct a molecular device using such molecules as templates to engineer interfacial spin transfer resulting from hybridization and magnetic exchange interaction with the surface of a ferromagnet; the device shows an unexpected interfacial magnetoresistance of more than 20 per cent near room temperature. Moreover, we successfully demonstrate the formation of a nanoscale magnetic molecule with a well-defined magnetic hysteresis on ferromagnetic surfaces. Owing to strong magnetic coupling with the ferromagnet, such independent switching of an adsorbed magnetic molecule has been unsuccessful with single-molecule magnets. Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.

Chiral-at-Metal Phosphorescent Square-Planar Pt(II)-Complexes from an Achiral Organometallic Ligand.

The synthesis and characterization of a new kind of cis- and trans-cyclometalated square-planar platinum(II) complexes is reported. Uncharged organometallic compounds carrying one or two of the C∧N-donor ligand LCN were prepared. Due to the heterobidentate coordination of the achiral chelate ligand, the formed [PtLCNCl(SEt2)], cis- and trans-[PtLCN2] complexes are chiral with the metal serving as the stereo center. The enantiomers of complex trans-[PtLCN2] could be separated and their absolute configuration was determined by anomalous X-ray diffraction, in accordance with CD spectroscopic results and TD-DFT calculations. All compounds were fully characterized by NMR spectroscopy, mass spectrometry and X-ray structure determination. The photophysical properties of trans-[PtLCN2] have been investigated showing phosphorescence in solution and in the solid state with a moderate quantum yield. For the enantiomers, strong circular dichroism (CD) and circularly polarized luminescence (CPL) effects were observed, rendering this new structural motif suitable for application in chiroptical and luminescent materials.

Introducing a Hydrogen-Bond Donor into a Weakly Nucleophilic Brønsted Base: Alkali Metal Hexamethyldisilazides (MHMDS, M=Li, Na, K, Rb and Cs) with Ammonia.

Alkali metal 1,1,1,3,3,3-hexamethyldisilazide (MHMDSs) are one of the most utilised weakly nucleophilic Brønsted bases in synthetic chemistry and especially in natural product synthesis. Like lithium organics, they aggregate depending on the employed donor solvents. Thus, they show different reactivity and selectivity as a function of their aggregation and solvation state. To date, monomeric LiHMDS with monodentate donor bases was only characterised in solution. Since the first preparation of LiHMDS in 1959 by Wannagat and Niederprüm, all efforts to crystallise monomeric LiHMDS in the absence of chelating ligands failed. Herein, we present ammonia adducts of LiHMDS, NaHMDS, KHMDS, RbHMDS and CsHMDS with unprecedented aggregation motifs: 1) The hitherto missing monomeric key compound in the LiHMDS aggregation architectures. Monomeric crystal structures of trisolvated LiHMDS (1) and NaHMDS (2), showing unique intermolecular hydrogen bonds, 2) the unprecedented tetrasolvated KHMDS (3) and RbHMDS (4) dimers and 3) the disolvated CsHMDS (5) dimer with very close intermolecular Si-CH3 ⋅⋅⋅Cs s-block "agostic" interactions have been prepared and characterised by single-crystal X-ray structure analysis.

Rational design of a face-centred square-cuboid coordination cage.

The simple synthetic conversion of a 90°-angled bis-pyridyl ligand into a tripodal tris-pyridyl ligand leads to the formal transformation of a cubic (a=b=c) into a square-cuboid (a=b≠c) coordination cage. Mathematical considerations associated with the ligand design, together with X-ray structure results, NMR spectroscopic and mass spectrometric characterization and molecular modeling of both coordination cages are presented and discussed.

Template control over dimerization and guest selectivity of interpenetrated coordination cages.

We have previously shown that the self-assembly of dibenzosuberone-based bis-monodentate pyridyl ligands L(1) with Pd(II) cations leads to the quantitative formation of interpenetrated coordination cages [BF4@Pd4L(1)8]. The BF4(-) anion inside the central cavity serves as a template, causing the outer two pockets to show a tremendous affinity for allosteric binding of two small chloride anions. Here we show that derivatization of the ligand backbone with a bulky aryl substituent allows us to control the dimerization and hence the guest-binding ability of the cage by the choice of the templating anion. Steric constraints imposed by L(2) prevent the large BF4(-) anion from serving as a template for the formation of interpenetrated double cages. Instead, a single isomer of the monomeric cage [Pd2L(2)4] is formed. Addition of the small anionic template Cl(-) permits dimerization, yielding the interpenetrated double cage [Cl@Pd4L(2)8], whose enlarged outer pockets show a preference for the binding of large anions such as ReO4(-).

The layered structure of [Na(NH3)4][Indenide] containing a square-planar Na(NH3)4(+) cation.

It's hip to be a square! The ammines [Li(NH(3))(4)][Ind] and [Na(NH(3))(4)][Ind] both contain a cation coordinated by four ammonia molecules. Whereas the first shows the anticipated tetrahedral coordination, in the second the metal coordination is unexpectedly square-planar. The solvent-separated ion pair forms a rippled layer structure of alternating planar Na(NH(3))(4)(+) cations and indenyl carbanions that is attributed to NH(3) ⋅⋅⋅π hydrogen bonds.

Preparation of RSn(I)-Sn(I)R with two unsymmetrically coordinated Sn(I) atoms and subsequent gentle activation of P4.

This article reports the reduction of [{2,6-iPr(2)C(6)H(3)NC(CH(3))}(2)C(6)H(3)SnCl] (1) with potassium graphite to afford a new distannyne [{2,6-iPr(2)C(6)H(3)NC(CH(3))}(2)C(6)H(3)Sn](2) (2) with a Sn-Sn bond. The most striking phenomenon of 2 is the presence of two differently coordinated Sn atoms (one is three-coordinated, the other is four-coordinated). The Sn-Sn bond length in 2 is 2.8981(9) Å, which is very close to that of a Sn-Sn single bond (2.97-3.06 Å). To elucidate the nature of the Sn-Sn bond, DFT calculation is carried out that shows there is no multiple bond character in 2. Furthermore, the reaction of 2 with white P(4) affords the tetraphosphabicylobutane derivative 3. This is the first example of gentle activation of white phosphorus by a compound with low valent Sn atoms. Note that, unlike 2, in 3 both Sn atoms are four-coordinated.

Reactivity studies of a disilene with N2O and elemental sulfur.

In a previous contribution, we have reported on a convenient and high yield synthesis of the disilene trans-[(TMS)(2)N(η(1)-Me(5)C(5))Si═Si(η(1)-Me(5)C(5))N(TMS)(2)] (2). Herein, we show the reactions of 2 with N(2)O and S(8). The former reaction affords two isomeric (cis- and trans-) dioxadisiletane ring compounds. To the best of our knowledge, this is the first report where both cis-and trans-isomers are isolated from the same disilene precursor and characterized structurally by single-crystal X-ray diffraction (XRD) studies. The reaction of 2 with elemental sulfur yields only the trans-isomer. To investigate this dissimilar reaction pattern exhibited by 2, computational studies were performed. Density functional theory (DFT) calculations showed that the two dioxadisiletane ring isomers are isoenergetic, with the trans isomer being slightly more stable than the cis counterpart, by 3.3 kcal/mol, while that is not the case with sulfur. All the isolated compounds are characterized by single-crystal XRD studies, multinuclear NMR spectroscopy, and electron ionization-mass spectrometry (EI-MS).

One pot synthesis of disilatricycloheptene analogue and Jutzi's disilene.

The reaction of LiN(TMS)(2) (TMS = Me(3)Si) with dichlorosilane (Me(5)C(5))SiHCl(2) (1) in a molar ratio of 3:2 at ambient temperature leads to the formation of the disilatricycloheptene analogue (2). Compound 2 consists of three (three-, four-, and five-membered) fused rings that together form a six-membered heterocyclic ring. However, the reaction of 1 with KN(TMS)(2) affords the formation of disilene of composition E-[(TMS)(2)N](η(1)-Me(5)C(5))Si═Si(η(1)-Me(5)C(5))[N(TMS)(2)] (3) in good yield. This is a convenient and facile route for the synthesis of 3 in a single step and supports the formation of (Me(5)C(5))SiN(TMS)(2) as an intermediate.

Monomeric Sn(II) and Ge(II) hydrides supported by a tridentate pincer-based ligand.

Herein we report the syntheses of terminal Sn(II) (3) and Ge(II) (4) hydrides from the corresponding chloride precursors [{2,6-iPr(2)C(6)H(3)NCMe}(2)C(6)H(3)MCl] (M = Sn (1), Ge (2)) using [K{B(sec-Bu)(3)}H] as a hydrogenating agent. Combination of steric shielding and intramolecular N → M interactions resulted in the protection of M(II)-H bonds.