Modelling Conformational Flexibility in a Spectrally Addressable Molecular Multi-Qubit Model System

Dipolar coupled multi-spin systems have the potential to be used as molecular qubits. Herein we report the synthesis of a molecular multi-qubit model system with three individually addressable, weakly interacting, spin1 / 2 ${{ 1/2 }}$ centres of differing g-values. We use pulsed Electron Paramagnetic Resonance (EPR) techniques to characterise and separately address the individual electron spin qubits; CuII , Cr7 Ni ring and a nitroxide, to determine the strength of the inter-qubit dipolar interaction. Orientation selective Relaxation-Induced Dipolar Modulation Enhancement (os-RIDME) detecting across the CuII spectrum revealed a strongly correlated CuII -Cr7 Ni ring relationship; detecting on the nitroxide resonance measured both the nitroxide and CuII or nitroxide and Cr7 Ni ring correlations, with switchability of the interaction based on differing relaxation dynamics, indicating a handle for implementing EPR-based quantum information processing (QIP) algorithms.

Synthesis and Characterisation of Luminescent [CrIII 2 L(μ-carboxylato)]3+ Complexes with High-Spin S=3 Ground States (L=N6 S2 donor ligand)

The synthesis, structure, magnetic, and photophysical properties of two dinuclear, luminescent, mixed-ligand [CrIII 2 L(O2 CR)]3+ complexes (R=CH3 (1), Ph (2)) of a 24-membered binucleating hexa-aza-dithiophenolate macrocycle (L)2- are presented. X-ray crystallographic analysis reveals an edge-sharing bioctahedral N3 Cr(μ-SR)2 (μ1,3 -O2 CR)CrN3 core structure with μ1,3 -bridging carboxylate groups. A ferromagnetic superexchange interaction between the electron spins of the Cr3+ ions leads to a high-spin (S=3) ground state. The coupling constants (J=+24.2(1) cm-1 (1), +34.8(4) cm-1 (2), H=-2JS1 S2 ) are significantly larger than in related bis-μ-alkoxido-μ-carboxylato structures. DFT calculations performed on both complexes reproduce both the sign and strength of the exchange interactions found experimentally. Frozen methanol-dichloromethane 1 : 1 solutions of 1 and 2 luminesce at 750 nm when excited into the 4 LMCT state on the 4 A2 → 2 T1 (ν2 ) bands (λexc =405 nm). The absolute quantum yields (ΦL ) for 1 and 2 were found to be strongly temperature dependent. At 77 K in frozen MeOH/CH2 Cl2 glasses, ΦL =0.44±0.02  (for 1), ΦL =0.45±0.02  (for 2).

The Synthesis and Characterisation of a Molecular Sea-Serpent: Studies of a {Cr24 Cu7 } Chain

A finite chain of thirty-one paramagnetic centers is reported, synthesized by reaction of hydrated chromium fluoride, copper carbonate and pivalic acid in the presence of 1,4,7,10-tetrazacyclododecane (cyclen). Magnetic studies show predominantly anti-ferromagnetic exchange leading to a high density of low-lying spin states and large saturation field.

Cyclic Heterometallic Interactions formed from a Flexible Tripeptide Complex Showing Effective Antiferromagnetic Spin Coupling

Developing tunable motifs for heterometallic interactions should be beneficial for fabricating functional materials based on cooperative electronic communications between metal centers. Reported here is the efficient formation of cyclic heterometallic interactions from a complex containing an artificial tripeptide with metal binding sites on its main chain and side chains. X-ray structural analysis and X-ray absorption spectroscopy revealed that the cyclic metal-metal arrangements arise from the amide groups connecting four square-planar Cu^II centers and four octahedral Ni^II centers in a cyclic manner. UV/Vis spectral studies suggested that this efficient formation was achieved by the selective formation of the square-planar Cu^II centers and a crystallization process. Magnetic measurements using SQUID clarified that the cyclic complex represented the S=2 spin state at low temperatures due to effective antiferromagnetic interactions between the Ni^II and Cu^II centers.

Hybrid Organic-Inorganic Rotaxanes, Including a Hetero-Hybrid [3]Rotaxane Featuring Two Distinct Heterometallic Rings and a Molecular Shuttle

[2] and [3] hybrid rotaxanes are reported based on {Ti₇ M} rings (M is a trivalent metal such as Fe^III or Ga^III ). NMR studies show that [2]rotaxanes can act as molecular shuttles, while EPR studies of [3]rotaxanes show weak interactions between the paramagnetic components of the supramolecular assemblies.

A pH-Dependent, Mechanically Interlocked Switch: Organometallic [2]Rotaxane vs. Organic [3]Rotaxane

We present the first [2]rotaxane featuring a functional organometallic host. In contrast to the known organic scaffolds, this assembly shows a high post-synthetic modifiability. The reactivity of the Ag₈ pillarplex host is fully retained, as is exemplified by the first transmetalation in a rotaxane framework to provide the respective Au₈ analogue. Additionally, a transformation under acidic conditions to give a purely organic [3]rotaxane is demonstrated which is reversible upon addition of a suitable base, rendering the assembly a pH-dependent switch. Hereby, it is shown that the mechanically interlocked nature of the system enhances the kinetic stability of the NHC host complex by a factor of >1000 and corresponds to the first observation of a stabilizing "rotaxand effect".

An Extensive Family of Heterometallic Titanium(IV)-Metal(III) Rings with Structure Control through Templates

A family of heterometallic [Cat][Ti_x MO_(x+1 )(O₂ C^t Bu)_2x+2 ] rings is reported where Cat=a secondary or tertiary alkyl ammonium ion, x=7, 8 or 9, and M=Fe^III , Ga^III , Cr^III , In^III and Al^III . The structures are regular polygons with eight, nine or ten vertices with each edge bridged by an oxide and two pivalates. The size of the ring formed is controlled by the alkylammonium cation present. In each case a homometallic by-product is found [Cat][Ti_x O_(x+1 )(O₂ C^t Bu)_2x-1 ].

Use of Supramolecular Assemblies as Lithographic Resists

A new resist material for electron beam lithography has been created that is based on a supramolecular assembly. Initial studies revealed that with this supramolecular approach, high-resolution structures can be written that show unprecedented selectivity when exposed to etching conditions involving plasmas.

Measuring Spin⋅⋅⋅Spin Interactions between Heterospins in a Hybrid [2]Rotaxane

Use of molecular electron spins as qubits for quantum computing will depend on the ability to produce molecules with weak but measurable interactions between the qubits. Here we demonstrate use of pulsed EPR spectroscopy to measure the interaction between two inequivalent spins in a hybrid rotaxane molecule.