Accuracy evaluation of an optical lattice clock with bosonic atoms

We report what we believe to be the first accuracy evaluation of an optical lattice clock based on the S01-->P03 transition of an alkaline earth boson, namely, Sr88 atoms. This transition has been enabled by using a static coupling magnetic field. The clock frequency is determined to be 429228066418009(32)Hz. The isotopic shift between Sr87 and Sr88 is 62188135Hz with fractional uncertainty 5x10(-7). We discuss the necessary conditions to reach a clock accuracy of 10(-17) or less by using this scheme.     

Dithiolene complexes as metalloligands: [Cu(en)2][Cu(mnt)2], an S = ½ spin chain

The paramagnetic dithiolene complex [Cu(mnt)₂]^2– (mnt: 1,2-dicyanoethylene-1,2-dithiolate) is used as metalloligand for coordination of dicationic [Cu(en)₂]²⁺ (en: ethylenediamine) complex, leading to the formation of chains of alternating [Cu(mnt)₂]^2–and [Cu(en)₂]²⁺ moieties through C≡N•••Cu•••N≡C trans coordination with N•••Cu distance of 2.664(4) Å and a noticeable deviation from linearity as the C≡N•••Cu angle amounts to 146.3(3)°. The [Cu(en)₂][Cu(mnt)₂] salt exhibits weak antiferromagnetic interactions between spin carriers along the chains and slightly stronger inter-chain [Cu(mnt)₂]•••[Cu(mnt)₂] antiferromagnetic interactions through intermolecular S•••S contacts.     

Temperature-dependent interfacial properties of hydrophobically end-modified poly(2-isopropyl-2-oxazoline)s assemblies at the air/water interface and on solid substrates

We describe herein the properties at the air/water (A/W) interface of hydrophobically end-modified (HM) poly(2-isopropyl-2-oxazoline)s (PiPrOx) bearing an n-octadecyl chain on both termini (telechelic HM-PiPrOx) or on one chain end (semitelechelic HM-PiPrOx) for different subphase temperatures and spreading solvents using the Langmuir film balance technique. The polymer interfacial properties revealed by the π–A isotherms depend markedly on the architecture and molecular weight of the polymer. On cold water subphases (14 °C), diffusion of PiPrOx chains onto water takes place for all polymers in the intermediate compressibility region (5 mN m⁻¹). At higher subphase temperatures (36 and 48 °C), the HM-PiPrOx film exhibited remarkable stability with time. Brewster angle microscopy (BAM) imaging of the A/W interface showed that the polymer assembly was not uniform and that large domains formed, either isolated grains or pearl necklaces, depending on the polymer structure, the concentration of the spreading solution and the subphase temperature. The Langmuir films were transferred onto hydrophilic substrates (silica) by the Langmuir–Blodgett (LB) technique and onto hydrophobic substrates (gold) by Langmuir–Schaefer (LS) film deposition, resulting in the formation of adsorbed particles ranging in size from 200 to 500 nm, depending on the polymer architecture and the substrate temperature. The particles presented “Janus”-like hydrophilic/hydrophobic characteristics.     

(Li/Ag)CoO2: a new intergrowth cobalt oxide composed of rock salt and delafossite layers

A new ordered (Li/Ag)CoO(2) layered compound with an unusual oxygen packing combining rock salt and delafossite layers is obtained during the (Li(+), Na(+))/Ag(+) ionic exchange from the OP4-(Li/Na)CoO(2) precursor. This compound is actually an intermediate step to the final D4-AgCoO(2) delafossite and can be isolated thanks to the kinetics difference between the Li(+)/Ag(+) and Na(+)/Ag(+) exchange processes. It crystallizes in the P6(3)/mmc space group with cell parameters a(hex.) = 2.848(3) ? and c(hex.) = 21.607(7) ?. The details of the structure as well as its thermal stability and transport properties are presented and discussed.     

Pyrazolylborates and their importance in tuning single-molecule magnet properties of {Fe(III)2Ni(II)} complexes

A new tricyanoferrate(III) building block and a trinuclear single-molecule magnet derivative are described. The treatment of a 2:1 ratio of [NEt(4)][(Tp*(Bn))Fe(III)(CN)(3)]·H(2)O·MeOH [1; Tp*(Bn) = tris(3,5-dimethyl-4-benzyl)pyrazolylborate] with nickel(II) trifluoromethanesulfonate gives {[(Tp*(Bn))Fe(III)(CN)(3)](2)[Ni(II)(DMF)(4)]}·2DMF (2; DMF = N,N-dimethylformamide). The symmetry-equivalent Fe(III)(LS) ions lead to a favorable alignment of anisotropy tensors (i.e., Fe···B axes) in 2, and an energy barrier of Δ(eff)/k(B) = 16.7 K is found for the S(T) = 2 complex.     

Water exchange of a ProHance MRI contrast agent: isomer-dependent free-energy landscapes and mechanisms

The water-exchange reaction in two diastereoisomers of the clinical magnetic resonance imaging contrast agent [Gd(HP-DO3A)(H(2)O)] (also known as ProHance) has been studied using ab initio simulations. On the basis of the molecular-level details of the mechanism derived from these simulations in aqueous solution, we unravel the underlying difference in the free energies and mechanisms of water exchange in the two diastereoisomers. These findings reveal the crucial role played by hydrogen-bonding dynamics and thus suggest their appropriate control in tailoring improved gadolinium-based constrast agents.     

Contribution of spin and anisotropy to single molecule magnet behavior in a family of bell-shaped Mn11Ln2 coordination clusters

The synthesis, structures, and magnetic properties of a family of isostructural "bell-shaped" heterometallic coordination clusters [Mn(III)(9)Mn(II)(2)La(III)(2)(μ(4)-O)(7)(μ(3)-O)(μ(3)-OH)(2)(piv)(10.8)(O(2)CC(4)H(3)O)(6.2)(NO(3))(2)(OH(2))(1.5)(MeCN)(0.5)]·12CH(3)CN·2H(2)O (1) and [Mn(III)(9)Mn(II)(2)Ln(2)(μ(4)-O)(7)(μ (3)-O)(μ(3)-OH)(2)(piv)(10.6)(O(2)CC(4)H(3)O)(6.4)(NO(3))(2)(OH(2))]·nCH(3)CN·H(2)O (Ln = Pr(III), n = 8 (2); Ln = Nd(III), n = 10 (3); Ln = Eu(III), n = 17 (4); Ln = Gd(III), n = 13 (5); piv = pivalate) are reported. The complexes were obtained from the reaction of [Mn(III)(2)Mn(II)(4)O(2)(piv)(10)(4-Me-py)(2.5)(pivH)(1.5)] and Ln(NO(3))(3)·6H(2)O in the presence of 2-furan-carboxylic acid (C(4)H(3)OCOOH) in CH(3)CN. Compounds 1-5 are isomorphous, crystallizing in the triclinic space group P1 with Z = 2. The Mn(III) and Mn(II) centers together form the shell of the bell, while the two Ln(III) centers can be regarded as the bell's clapper. The magnetic properties of 1-4 reveal dominant antiferromagnetic interactions between the magnetic centers leading to small spin ground states; while those of 5 indicate similar antiferromagnetic interactions between the manganese ions but with unusually strong ferromagnetic interactions between the Gd(III) ions leading to a large overall spin ground state of S = 11-12. While ac and dc magnetic measurements confirmed that Mn(11)Gd(2) (5) is a single-molecule magnet (SMM) showing hysteresis loops at low temperatures, compounds 1-4 do not show any slow relaxation of the magnetization, indicating that the S = 7 spin of the ferromagnetic Gd(2) unit in 5 is a necessary contribution to its SMM behavior.