Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6

Few examples of magnetic systems displaying a transition to pure dipolar magnetic order are known to date, and single-molecule magnets can provide an interesting example. The molecular cluster spins and thus their dipolar interaction energy can be quite high, leading to reasonably accessible ordering temperatures, provided the crystal field anisotropy is sufficiently small. This condition can be met for molecular clusters of sufficiently high symmetry, as for the Mn6 compound studied here. Magnetic specific heat and susceptibility experiments show a transition to ferromagnetic dipolar order at T_{c} = 0.16 K. Classical Monte-Carlo calculations indeed predict ferromagnetic ordering and account for the correct value of T_{c}. In high magnetic fields we detected the contribution of the ^{55}Mn nuclei to the specific heat, and the characteristic timescale of nuclear relaxation. This was compared with results obtained directly from pulse-NMR experiments. The data are in good mutual agreement and can be well described by the theory for magnetic relaxation in highly polarized paramagnetic crystals and for dynamic nuclear polarization, which we extensively review. The experiments provide an interesting comparison with the recently investigated nuclear spin dynamics in the anisotropic single molecule magnet Mn12-ac.Comment: 19 pages, 11 eps figures. Contains extensive discussions on dipolar ordering, specific heat and nuclear relaxation in molecular magnet

Long-range ferromagnetic dipolar ordering of high-spin molecular clusters

We report the first example of a transition to long-range magnetic order in a purely dipolarly interacting molecular magnet. For the magnetic cluster compound Mn6O4Br4(Et2dbm)6, the anisotropy experienced by the total spin S=12 of each cluster is so small that spin-lattice relaxation remains fast down to the lowest temperatures, thus enabling dipolar order to occur within experimental times at Tc = 0.16 K. In high magnetic fields, the relaxation rate becomes drastically reduced and the interplay between nuclear- and electron-spin lattice relaxation is revealed.Comment: 4 pages, 4 .eps figures; accepted for publication in Phys. Rev. Let

A heterometallic [LnLn′Ln] lanthanide complex as a qubit with embedded quantum error correction

We show that a [Er-Ce-Er] molecular trinuclear coordination compound is a promising platform to implement the three-qubit quantum error correction code protecting against pure dephasing, the most important error in magnetic molecules. We characterize it by preparing the [Lu-Ce-Lu] and [Er-La-Er] analogues, which contain only one of the two types of qubit, and by combining magnetometry, low-temperature specific heat and electron paramagnetic resonance measurements on both the elementary constituents and the trimer. Using the resulting parameters, we demonstrate by numerical simulations that the proposed molecular device can efficiently suppress pure dephasing of the spin qubits

Hanford Site River Protection Project High-Level Waste Safe Storage and Retrieval

This paper provides an update from last year and describes project successes and issues associated with the management and work required to safely store, enhance readiness for waste feed delivery, and prepare for treated waste receipts for the approximately 53 million gallons of mixed and high-level waste currently in aging tanks at the Hanford Site. The Hanford Site is a 560 square-mile area in southeastern Washington State near Richland, Washington

Polynuclear complexes as precursor templates for hierarchical microporous graphitic carbon: An unusual approach

YesA highly porous carbon was synthesized using a coordination complex as an unusual precursor. During controlled pyrolysis, a trinuclear copper complex, [CuII3Cl4(H2L)2]·CH3OH, undergoes phase changes with melt and expulsion of different gases to produce a unique morphology of copper-doped carbon which, upon acid treatment, produces highly porous graphitic carbon with a surface area of 857 m2 g–1 and a gravimetric hydrogen uptake of 1.1 wt % at 0.5 bar pressure at 77 K.EPSRC (EP/R01650X/1 for VPT, and EP/E040071/1 for MT) and the University of Bristo

Lanthanoid “Bottlebrush” Clusters: Remarkably Elongated Metal-Oxo Core Structures with Controllable Lengths

Large metal-oxo clusters consistently assume spherical or regular polyhedral morphologies rather than high-aspect-ratio structures. Access to elongated core structures has now been achieved by the reaction of lanthanoid salts with a tetrazole-functionalized calixarene in the presence of a simple carboxylate coligand.The resulting Ln19 and Ln12 clusters are constructed from apex-fused Ln5O6 trigonal bipyramids and are formed consistently under a range of reaction conditions and reagent ratios. Altering the carboxylate coligandstructure reliably controls the cluster length, giving access to a new class of rod-like clusters of variable length

In search for molecules displaying ferromagnetic exchange: multiple-decker Ni12 and Ni16 complexes from the use of pyridine-2-amidoxime

The use of pyridine-2-amidoxime (pyaoxH2) in Ni chemistry has provided access to a dodecanuclear complex and a hexadecanuclear Ni cluster, namely [Ni12(pyaox)6(pyaoxH)6(MeOH)2Cl2]Cl4·5MeOH (1·5MeOH) and [Ni16(pyaox)8(pyaoxH)8(MeOH)4](SO4)4·10H2O·26MeOH (2·10H2O·26MeOH). Complex 1·5MeOH was isolated by the reaction of NiCl2·6H2O, pyaoxH2 and NaOMe in a 1 : 1 : 2 molar ratio in MeOH in 60% yield. Treatment of NiSO4·6H2O with pyaoxH2 and NEt3 in a 1 : 1 : 2 molar ratio in MeOH afforded 2·10H2O·26MeOH in good yield (65%). The two compounds display a multi-decker configuration based on stacked Ni4 layers, {Ni4(pyaox)2(pyaoxH)2}2+x (x = 3, 1·5MeOH; x = 4, 2·10H2O·26MeOH); each deck consists of two square planar and two octahedral NiII centres. The number of decks observed in 1·5MeOH and 2·10H2O·26MeOH depends on the nature of the inorganic anion that is present in the reaction system, which provides elements of synthetic control towards new high nuclearity NiII species. 2·10H2O·26MeOH is the first structurally characterized complex of any metal displaying a quadruple-decker configuration, being also the highest nuclearity metal cluster bearing pyaoxH2 and the highest nuclearity NiII cluster with any type of 2-pyridyl oxime. Each cluster cation displays ferromagnetic exchange between the octahedral NiII ions resulting in a spin ground state of S = 6 for 1 and S = 8 for 2. Magnetothermal studies have been performed and discussed for both clusters.CP and CE thank the School of Chemistry, NUI Galway, for the financial support. RI thanks the Royal Society of Edinburgh and ME thanks Spanish MINECO (MAT2015-68204-R) for funding. LCS acknowledges the financial support by FEDER (Fundo Europeu de Desenvolvimento Regional) through PT2020, by FCT (Fundação para a Ciência e a Tecnologia) for the research centre REQUIMTE/LAQV (UID/QUI/50006/2013) and for the grant SFRH/BPD/111899/2015.Peer Reviewe