No abstract

Using X-band pulsed electron spin resonance, we report the intrinsic spin-lattice (T1) and phase coherence (T2) relaxation times in molecular nanomagnets for the first time. In Cr7M heterometallic wheels, with M = Ni and Mn, phase coherence relaxation is dominated by the coupling of the electron spin to protons within the molecule. In deuterated samples T2 reaches 3 µs at low temperatures, which is several orders of magnitude longer than the duration of spin manipulations, satisfying a prerequisite for the deployment of molecular nanomagnets in quantum information applications.Certain computational tasks can be efficiently implemented using quantum logic, in which the informationcarrying elements are permitted to exist in quantum superpositions [1]. To achieve this in practice, a physical system that is suitable for embodying quantum bits (qubits) must be identified. Some proposed scenarios employ electron spins in the solid state, for example phosphorous donors in silicon [2], quantum dots [3], heterostructures [4] and endohedral fullerenes [5,6], motivated by the long electron-spin relaxation times exhibited by these systems. An alternative electron-spin based proposal exploits the large number of quantum states and the non-degenerate transitions available in high spin molecular magnets [7,8]. Although these advantages have stimulated vigorous research in molecular magnets [9,10,11], the key question of whether the intrinsic spin relaxation times are long enough has hitherto remained unaddressed. Here we show, using pulsed electron spin resonance experiments on heterometallic wheels, that the relaxation times in molecular magnets can significantly exceed the duration of coherent manipulations, a prerequisite for the deployment of these systems in quantum information applications.Molecular magnets comprising clusters of exchanged coupled transition metal ions have been studied extensively in recent years [12]. They can exhibit a substantial ground state spin with a large and negative zerofield splitting (ZFS), leading to a spontaneous magnetic moment parallel to the easy axis. In the absence of a magnetic field, the configurations in which the moment is 'up' or 'down' relative to the easy axis are degenerate, and this bistable nature has stimulated interest in the application of magnetic clusters as classical [13] or quantum [7,8,9, 11] information elements.Molecules in this class have been synthesised with widely varying properties, from the S = 10 highly axial Mn 12 -acetate [14], to the diamagnetic ring Cr 8 F 8 Piv 16 [15,16]. A key recent chemical advance is the the development of procedures for magnetically 'doping' a diamagnetic cluster to synthesise paramagnetic molecules in a systematic and controllable way [17]. Thus, substituting a Cr 3+ (s = 3/2) by a Mn 2+ (s = 5/2) or a Ni 2+ (s = 1) generates the S = 1 Cr 7 Mn or the S = 1/2 Cr 7 Ni respectively.Many clusters have been investigated using thermodynamic probes such as magnetization [18] and heat capacity [19], and spectroscopic probes such as neutr...

We report a monometallic dysprosium complex, [Dy(O Bu) (py) ][BPh ] (5), that shows the largest effective energy barrier to magnetic relaxation of U =1815(1) K. The massive magnetic anisotropy is due to bis-trans-disposed tert-butoxide ligands with weak equatorial pyridine donors, approaching proposed schemes for high-temperature single-molecule magnets (SMMs). The blocking temperature, T , is 14 K, defined by zero-field-cooled magnetization experiments, and is the largest for any monometallic complex and equal with the current record for [Tb N {N(SiMe ) } (THF) ].

Two ligands have been synthesized by derivatisation of cyanuric chloride: 6-(diethylamino)-2,4-disulfanyl-1,3,5triazine (H 2 SSta) 1 and 6-(diethylamino)-2-hydroxo-4-sulfanyl-1,3,5-triazine (H 2 OSta) 2 have been characterised by X-ray crystallography, which shows intermolecular hydrogen bonding in the solid state, leading to dimers of 1 and ribbons of 2. On reaction with metal salts both ligands undergo oligomerisation reactions. Compound 1 reacts with nickel chloride to form a mononuclear complex, [Ni{(Sta)S(S 2 ta)}] 3. In 3 two triazine ligands have reacted, to form a tetradentate ligand in which two triazine rings are bridged by a sulfur group, with a co-ordinated disulfide group present on one ring and a co-ordinated thiolate on the second. Compound 2 reacts with cobalt() chloride to form a cage complex, [Co 6 NaO(OStaH) This complicated structure contains two polydentate ligands formed by linking triazine groups through a bridging sulfur. The cage contains four cobalt() and two cobalt() sites which are assigned by bond length considerations. The compound [Co(OSta) 3 ] 5 co-crystallises with 4, and its structure has also been determined.

Single-molecule magnets are compounds that exhibit magnetic bistability caused by an energy barrier for the reversal of magnetization (relaxation). Lanthanide compounds are proving promising as single-molecule magnets: recent studies show that terbium phthalocyanine complexes possess large energy barriers, and dysprosium and terbium complexes bridged by an N2(3-) radical ligand exhibit magnetic hysteresis up to 13 K. Magnetic relaxation is typically controlled by single-ion factors rather than magnetic exchange (whether one or more 4f ions are present) and proceeds through thermal relaxation of the lowest excited states. Here we report polylanthanide alkoxide cage complexes, and their doped diamagnetic yttrium analogues, in which competing relaxation pathways are observed and relaxation through the first excited state can be quenched. This leads to energy barriers for relaxation of magnetization that exceed 800 K. We investigated the factors at the lanthanide sites that govern this behaviour.