Syntheses and Crystal Structures of a Series of Manganese-Lanthanide-Sodium 12-Metallacrown-4 Dimers

A series of heterotrimetallic manganese-lanthanide-sodium dimer metallacrowns has been synthesized and characterized by single-crystal X-ray analysis: {LnNa[12-MC_{Mn(III)N(shi)}-4]}₂(iph)₄, where Ln^III?=?La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14), and Y (15); MC is metallacrown; shi^3? is salicylhydroximate; and iph^2? is isophthalate. The manganese(III) ions and shi^3? ligands generate the 12-MC-4 framework with one Ln^III and Na⁺ ion bound to each [12-MC_{Mn(III)N(shi)}-4] on opposite sides of the central MC cavity. The carboxylate groups of the isophthalate ligands bridge between the central Ln^III ion and each ring Mn^III ion, and the meta-arrangement of the carboxylate groups joins two LnNa[12-MC_{Mn(III)N(shi)}-4] units together to form the dimer through the Ln^III ions, which reside on the interior of the molecule. The identity of the central Ln^III ion slightly impacts the size the [12-MC_{Mn(III)N(shi)}-4] framework. As the crystal radius of the Ln^III ion increases from Lu^III (1.02 Å) to La^III (1.19 Å), the 12-MC-4 framework expands to accommodate the larger Ln^III ion as the MC cavity increases in size (0.53 Å for Lu^III to 0.58 Å for La^III) and the average cross cavity Mn^III-Mn^III and oxime oxygen-oxime oxygen distances also increase (Mn^III-Mn^III distances: 6.48 Å for Lu^III to 6.52 Å for La^III; O_oxime-O_oxime distances: 3.66 Å for Lu^III to 3.75 Å for La^III). In addition, the larger Ln^III ions reside further from the MC cavity as indicated by the Ln^III-oxime oxygen mean plane (O_oxMP) distance. The Ln^III-O_oxMP distance steadily decreases from La^III (1.7527(12) Å) to Lu^III (1.5575(15) Å).

Graphic Abstract

The complex {LaNa[12-MC_{Mn(III)N(shi)}-4]}₂(iph)₄(DMF)₆(H₂O)₂ is a dimer of [12-MC-4] molecules linked by four isophthalate anions

     

Acyclic 1,4-stereocontrol via reductive 1,3-transpositions

One-pot reduction/allylic diazene rearrangement of lactic acid- and mandelic acid-derived alpha,beta-unsaturated tosyl hydrazones leads to 1,4-syn- or 1,4-anti-E-2-alkenyl arrays in high yield and diastereoselectivity. Either the syn or the anti diastereomer can be prepared by choosing the appropriate alkene stereoisomer of the hydrazone. The E-alkenes led to the 1,4-syn isomers, while the Z-alkenes led to the 1,4-anti isomers, both with > or =20:1 diastereoselectivity.     

Preparation of cyclophanes by room-temperature ring-closing alkyne metathesis with imidazolin-2-iminato tungsten alkylidyne complexes

Room-temperature ring-closing alkyne metathesis of 1,2-, 1,3-, and 1,4-bis(3-pentynyloxymethyl)benzenes has been investigated in the presence of catalytic amounts of an imidazolin-2-iminato tungsten alkylidyne complex. The m- and p-diynes selectively form the respective [10]metacyclophane or [10.10]paracyclophane, respectively, whereas a mixture of monomeric and dimeric cycloalkynes is obtained in the case of the o-diyne. DFT calculations reveal that the different selectivities can be attributed to the relative thermodynamic stability of the emerging cyclophanes.     

Gamma limit of the nonself-dual Chern-Simons-Higgs energy

We consider the Gamma limit of the Abelian Chern-Simons-Higgs energy

     

Invariant measures and maximal L2 regularity for nonautonomous Ornstein-Uhlenbeck equations

We characterize the domain of the realizations of a linear parabolicoperator defined in L² spaces with respect to a suitable measurethat is invariant for the associated evolution semigroup. Asa byproduct, we obtain optimal L² regularity results for evolutionequations with time-dependant Ornstein–Uhlenbeck operators.     

A dynamic micromixer for arbitrary control of disguised chemical selectivity

A new type of dynamic micromixer combining the concepts of parallel multi-lamination and hydrodynamic focusing was developed for arbitrary control of disguised chemical selectivity.     

The strength of the σ-, π- and δ-bonds in Re2Cl 8 2−

The geometry of Re₂Cl₈²⁻ has been optimized for the eclipsed (D _4h ) equilibrium conformation and for the staggered (D _4d ) conformation at BP86/TZ2P. The nature of the Re–Re bond which has a formal bond order four has been studied with an energy decomposition analysis (EDA). The EDA investigation indicates that the contribution of the b ₂ (δ _xy ) orbitals to the Re–Re bond in the ground state is negligibly small. The vertical excitation of one and two electrons from the bonding δ orbital into the antibonding δ* orbitals yielding the singly and doubly excited states and gives a destabilization of 17.5 and 36.1 kcal/mol, respectively, which is nearly the same as the total excitation energies. The preference for the D _4h geometry with eclipsing Re–Cl bonds is explained in terms of hyperconjugation rather than δ bonding. This is supported by the calculation of the triply bonded Re₂Cl₈ which also has an eclipsed energy minimum structure. The calculations also suggest that the Re–Re triple bond in Re₂Cl₈ is stronger than the Re–Re quadruple bond in Re₂Cl₈²⁻. A negligible contribution of the δ orbital to the metal–metal bond strength is also calculated for Os₂Cl₈ which is isoelectronic with Re₂Cl₈²⁻. Contribution of the Mark S. Gordon 65th Birthday Festschrift Issue. Theoretical Studies of Inorganic Compounds. 38. Part 37 (2006) Bessac F, Frenking G, Inorg Chem 45:6956.