Synthesis and reactions of N-heterocycle functionalised variants of heterometallic {Cr7Ni} rings.

Here we present a series of linked cage complexes of functionalised variants of the octametallic ring {Cr7Ni} with the general formula [(n)Pr2NH2][Cr7NiF8(O2C(t)Bu)15(O2CR)], where HO2CR is a N-heterocycle containing carboxylic acid. These compounds are made by reacting [(n)Pr2NH2][Cr7NiF8(O2C(t)Bu)15(O2CR)] with a variety of simple metal salts and metal dimers. The carboxylic acids studied include iso-nicotinic acid, 3-(4-pyridyl)acrylic acid and 4-pyridazine carboxylic acid. These new linked cage complexes have been studied structurally and the study highlights the versatility of functionalised {Cr7Ni} as a Lewis base ligand. As {Cr7Ni} is a putative molecular electron spin qubit this work contributes to our understanding of the chemistry that might be required to assemble molecular spin qubits.

Molecular nanomagnets with switchable coupling for quantum simulation.

Molecular nanomagnets are attractive candidate qubits because of their wide inter- and intra-molecular tunability. Uniform magnetic pulses could be exploited to implement one- and two-qubit gates in presence of a properly engineered pattern of interactions, but the synthesis of suitable and potentially scalable supramolecular complexes has proven a very hard task. Indeed, no quantum algorithms have ever been implemented, not even a proof-of-principle two-qubit gate. Here we show that the magnetic couplings in two supramolecular {Cr7Ni}-Ni-{Cr7Ni} assemblies can be chemically engineered to fit the above requisites for conditional gates with no need of local control. Microscopic parameters are determined by a recently developed many-body ab-initio approach and used to simulate quantum gates. We find that these systems are optimal for proof-of-principle two-qubit experiments and can be exploited as building blocks of scalable architectures for quantum simulation.

Rings and threads as linkers in metal-organic frameworks and poly-rotaxanes.

Coordination polymers and metal-organic rotaxane frameworks are reported where the organic linker is replaced by functionalised inorganic clusters that act as bridging ligands.

Chemical control of spin propagation between heterometallic rings.

We present a synthetic, structural, theoretical, and spectroscopic study of a family of heterometallic ring dimers which have the formula [{Cr(7)NiF(3)(Etglu)(O(2)CtBu)(15)}(2)(NLN)], in which Etglu is the pentadeprotonated form of the sugar N-ethyl-D-glucamine, and NLN is an aromatic bridging diimine ligand. By varying NLN we are able to adjust the strength of the interaction between rings with the aim of understanding how to tune our system to achieve weak magnetic communication between the spins, a prerequisite for quantum entanglement. Micro-SQUID and EPR data reveal that the magnetic coupling between rings is partly related to the through-bond distance between the spin centers, but also depends on spin-polarization mechanisms and torsion angles between aromatic rings. Density functional theory (DFT) calculations allow us to make predictions of how such chemically variable parameters could be used to tune very precisely the interaction in such systems. For possible applications in quantum information processing and molecular spintronics, such precise control is essential.

Synthesis, spectroscopy and electronic structure of the vinylidene and alkynyl complexes [W(C=CHR)(dppe)(η-C7H7)](+) and [W(C≡CR)(dppe)(η-C7H7](n+) (n = 0 or 1).

The first examples of vinylidene complexes of the cycloheptatrienyl tungsten system [W(C=CHR)(dppe)(η-C7H7)](+) (dppe = Ph2PCH2CH2PPh2; R = H, 3; Ph, 4; C6H4-4-Me, 5) have been synthesised by reaction of [WBr(dppe)(η-C7H7)], 1, with terminal alkynes HC≡CR; a one-pot synthesis of 1 from [WBr(CO)2(η-C7H7)] facilitates its use as a precursor. The X-ray structure of 4[PF6] reveals that the vinylidene ligand substituents lie in the pseudo mirror plane of the W(dppe)(η-C7H7) auxiliary (vertical orientation) with the phenyl group located syn to the cycloheptatrienyl ring. Variable temperature ¹H NMR investigations on [W(C=CH2)(dppe)(η-C7H7)][PF6], 3, estimate the energy barrier to rotation about the W=C(α) bond as 62.5 ± 2 kJ mol⁻¹; approximately 10 kJ mol⁻¹ greater than for the molybdenum analogue. Deprotonation of 4 and 5 with KOBu(t) yields the alkynyls [W(C≡CR)(dppe)(η-C7H7)] (R = Ph, 6; C6H4-4-Me, 7) which undergo a reversible one-electron oxidation at a glassy carbon electrode in CH2Cl2 with E(½) values approximately 0.12 V negative of Mo analogues. The 17-electron radicals [6](+) and [7](+) have been investigated by spectroelectrochemical IR, UV-visible and EPR methods. The electronic structures of representative vinylidene (3) and alkynyl (6) complexes have been investigated at the B3LYP/Def2-SVP level. In both cases, electronic structure is characterised by a frontier orbital with significant metal d(z²)character and this dominates the structural and spectroscopic properties of the system.