The thermally stable tris(pyridyl) Al(III) complex [MeAl(2-py)3Li·THF] (1·THF), obtained from the reaction of lithiopyridine [2-pyLi] with MeAlCl2 (3:1 molar equiv, respectively), functions as a pyridyl-transfer reagent, as exemplified by the reaction of 1·THF with CuCl (1:1 molar equiv), which gives the Cu(I) organometallic [{Cu(2-py)}3]∞ (2). The solid-state structures of 1, the dimer [MeAl(2-py)3Li]2 ([1]2), and 2 are reported. Complex 2, which cannot be obtained by direct reaction of [2-pyLi] with CuCl, has a polymeric structure in which macrocyclic [Cu(2-py)]3 ring units form infinite offset stacks associated by short Cu···Cu interactions between three- and four-coordinate Cu(I) centers (2.762(3) Å).

The hybrid dibismuthines O{(CH2)2BiPh2}2, MeN(CH2-2-C6H4BiR2)2, and S(CH2-2-C6H4BiR2)2 (R = Me, Ph), have been prepared and characterized by microanalysis, 1H and 13C{1H} NMR spectroscopy, and FAB mass spectrometry. The X-ray structures of O{(CH2)2BiPh2}2 and S(CH2-2-C6H4BiPh2)2 show close to symmetrical hypervalent interactions between the O or S atoms and both bismuth centers. The antimony analogue S(CH2-2-C6H4SbMe2)2 is quaternized by MeI to [S(CH2-2-C6H4SbMe3)2]I2, which also shows a hypervalent S···Sb interaction, but in this case to only a single antimony center. Complexes of these and related ligands with the CpFe(CO)2 + group, of the type [{CpFe(CO)2}2L][BF4]2 (L = O{(CH2)2BiPh2}2, MeN(CH2-2-C6H4BiR2)2, S(CH2-2-C6H4BiR2)2, O{(CH2)2SbR2}2, S(CH2-2-C6H4SbMe2)2, MeN(CH2-2-C6H4SbMe2)2, Ph2Sb(CH2)3SbPh2), have been prepared and characterized by microanalysis (antimony complexes only), 1H and 13C{1H} NMR and IR spectroscopy, and ES+ mass spectrometry. The X-ray crystal structure of [{CpFe(CO)2}2{O{(CH2)2SbMe2}2}][BF4]2 shows a hypervalent Sb···O contact to one of the antimony centers, whereas no hypervalent contacts are seen in the structure of [{CpFe(CO)2}2{MeN(CH2-2-C6H4SbMe2)2}][BF4]2. IR (carbonyl region) and NMR spectroscopy indicate that, uniquely, [{CpFe(CO)2}2{MeN(CH2-2-C6H4BiPh2)2}][BF4]2 shows hypervalent N···Bi interactions in both the solid and solution, but for the other dibismuthine complexes, there is evidence for inequivalence of the iron centers (and hence hypervalency) only in the solid state. Spectroscopic data indicate that hypervalent interactions are absent in [{CpFe(CO)2}2{MeN(CH2-2-C6H4SbMe2)2}][BF4]2 and [{CpFe(CO)2}2{S(CH2-2-C6H4SbMe2)2}][BF4]2, but present in solid [{CpFe(CO)2}2{O{(CH2)2SbR2}2}][BF4]2. The preparation and X-ray structure of [CpFe(CO)2{BiPh2(o-C6H4OMe)}][BF4] is also reported, but attempts to isolate [CpFe(CO)2(BiPhMe2)]][BF4] resulted in rapid scrambling of the substituents at bismuth to give [CpFe(CO)2(BiPh3−n Me n )][BF4] (n = 0−3).

We review recent efforts and discuss future prospects in research employing x-ray photon correlation spectroscopy (XPCS) to interrogate the nanometer-scale structural dynamics of soft materials undergoing in situ mechanical deformation and flow. Examples of such rheo-XPCS experiments include those incorporating conventional homogeneous shear deformation, including notably large amplitude oscillatory shear (LAOS), as well as other modes of flow and deformation, such as tensile strain and flow within microfluidic environments. Particular attention is given to opportunities in such studies to reveal the structural dynamics associated with nonlinear rheological behavior such as yielding. We also review recent related work employing XPCS as a microrheological tool by tracking nanoparticle mobility within complex fluids.

Contaminated peanut butter and peanut products caused a nationwide salmonellosis outbreak. Ingredient-driven outbreaks are challenging to detect and may lead to widespread contamination of numerous food products.

Buoyant plumes, evolving free of boundary constraints, may develop well-defined mushroom-shaped heads. In conventional plumes, overturning flow in the head entrains less buoyant fluid from the surroundings as the head rises, robbing the plume of its driving force. We consider here a new type of plume in which the source of buoyancy is an autocatalytic chemical reaction. The reaction occurs at a sharp front which separates reactants from less dense products. In this type of autocatalytic plume, entrainment assists the reaction, producing new buoyancy which fuels an accelerating plume head. When the head has grown to a critical size, it detaches from the upwelling conduit, forming an accelerating, buoyant vortex ring. A second-generation head then develops at the point of detachment. Multiple generations of autocatalytic vortex rings can detach from a single triggering event.

Reactions of the Al(III) complex [{MeAl(2-py)3}Li·THF] (1), containing the tripodal [MeAl(2-py)3]- ligand, with [(C7H8)Mo(CO)3], CaI2, and ZnCl2 give the trimetallic and bimetallic complexes [{MeAl(2-py)3}Mo(CO)3Li(THF)3] (2), [{MeAl(2-py)3}2Ca] (3), and [{MeAl(2-py)3}ZnCl] (4), respectively. [{ n BuIn(2-py)3}Li·THF] (5), an InIII analogue of 1 containing the [ n BuIn(2-py)3]- anion, is obtained by the one-pot reaction of n BuLi with InCl3 followed by reaction with 2-Li-py. Complex 5 reacts with [(C7H8)Mo(CO)3] to give [{ n BuIn(2-py)3}Mo(CO)3Li(THF)2]∞ (6) (analogous to the AlIII complex 2). The X-ray structures of the new complexes 2, 3, 4, 5, and 6 are reported.

We report x-ray photon correlation spectroscopy experiments on a concentrated nanocolloidal gel subject to in situ oscillatory shear strain. The strain causes periodic echoes in the speckle pattern that lead to peaks in the intensity autocorrelation function. Above a threshold strain that is near the first yield point of the gel, the peak amplitude decays exponentially with the number of shear cycles, signaling irreversible particle rearrangements. The wave-vector dependence of the decay rate reveals a power-law distribution in the size of regions undergoing shear-induced rearrangement. The gel also displays strain softening well below the threshold, indicating a range of strains at which the rheology is nonlinear but the microscopic deformations are reversible.

A starting plume or jet has a well-defined, evolving head that is driven through the surrounding quiescent fluid by a localized flux of either buoyancy or momentum, or both. We studied the scaling and morphology of starting plumes produced by a constant flux of buoyant fluid from a small, submerged outlet. The plumes were laminar and spanned a wide range of plume Richardson numbers Ri. Ri is the dimensionless ratio of the buoyancy forces to inertial effects, and is thus our measurements crossed over the transition between buoyancy-driven plumes and momentum-driven jets. We found that the ascent velocity of the plume, nondimensionalized by Ri, exhibits a power law relationship with Re, the Reynolds number of the injected fluid in the outlet pipe. We also found that as the threshold between buoyancy-driven and momentum-driven flow was crossed, two distinct types of plume head mophologies existed: confined heads, produced in the Ri > 1 regime, and dispersed heads, which are found in the Ri < 1 regime. Head dispersal is caused by a breakdown of overturning motion in the head, and a local Kelvin-Helmholtz instability on the exterior of the plume.Comment: 8 pages, 8 figures, accepted for publication in Physics of Fluids (final version with corrections