We show that the electron spin phase memory time, the most important property of a molecular nanomagnet from the perspective of quantum information processing, can be improved dramatically by chemically engineering the molecular structure to optimize the environment of the spin. We vary systematically each structural component of the class of antiferromagnetic Cr(7)Ni rings to identify the sources of decoherence. The optimal structure exhibits a phase memory time exceeding 15  μs.

We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2'-bipyridine]. The complex crystallizes in the trigonal space group R3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = -324 cm(-1)). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = (1)/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.

The sugar-modified Schiff base ligand benzyl 2-deoxy-2-salicylideneamino-alpha-D-glucopyranoside H 2L, prepared by condensation of salicylaldehyde and the monomeric chitosan analogue benzyl 2-deoxy-2-amino-alpha-D-glucopyranoside, reacts with copper(II) acetate to form a self-assembled, alkoxo-bridged tetranuclear homoleptic copper(II) complex [{Cu(L)}4] (4) with Cu4O4 heterocubane core. The chiral complex 4 crystallizes in the space group P2 12 12 1. The tetranuclear complex 4 is composed of two dinuclear {Cu(L)}2 entities linked by the four mu 3-bridging C-3 alkoxide oxygen atoms of the sugar backbone. The preorganization of the dimeric {Cu(L)}2 entities is enforced by strong hydrogen bonds between the phenolate oxygen atom and the C-4 hydroxy group of the two constituting chiral monomeric building blocks. Therefore the Cu4O4 core can be classified as a type I or 2 + 4 cubane. The chirality of the structure is confirmed by circular dichroism (CD) spectra, which reveal a significant dichroism associated with the copper centered transitions at around 600 nm. Temperature dependent magnetic susceptibility measurements indicate ferromagnetic exchange interactions in complex 4. Fitting of the experimental data with a two J model based on the 2 + 4 topology ( H = - J1(S1S3 + S2S4) - J2(S1 + S3)(S2 + S4)) leads to exchange coupling constants of J1 = 64 and J2 = 4 cm(-1). The observed ferromagnetic coupling can be attributed to the very small Cu-O-Cu bridging angles within the Cu2O2 core of the constituting dimeric entities, which are a result of the conformational requirements introduced by the sugar backbone. 4 is not only the first example of an alkoxo-bridged tetranuclear copper(II) complex with Cu4O4 core representing the 2 + 4 cubane class with ferromagnetic ground state but also a rare example for the class of molecules combining a ferromagnetic ground state with optical activity. The ferromagnetic S = 2 ground state of 4 is confirmed by magnetization measurements and ESR spectroscopy.

The influence of the counteranion on the ability of the mesogenic cation 1-methyl-3-dodecyl-triazolium to form mesophases is explored. To that avail, salts of the cation with anions of different size, shape, and hydrogen bonding capability such as Cl -, Br -, I -, I 3 -, PF 6 -, and Tf 2 N -[bis(trifluorosulfonyl)amide] were synthesized and characterized. The crystal structures of the bromide, the iodide, and the triiodide reveal that the cations form bilayers with cations oriented in opposite directions featuring interdigitated alkyl tails. Within the layers, the cations are separated by anions. The rod-shaped triiodide anion forces the triazolium cation to align with it in this crystal structure but due to its space requirement reduces the alkyl chain interdigitation which prevents the formation of a mesophase. Rather the compound transforms directly from a crystalline solid to an (ionic) liquid like the analogous bis(trifluorosulfonyl)amide. In contrast, the simple halides and the hexafluorophosphate form liquid crystalline phases. Their clearing points shift with increasing anion radius to lower temperatures. Disciplines Ceramic Materials | Complex Fluids | Other Chemical Engineering | Other Materials Science and Engineering CommentsReprinted with permission from Cryst. Growth Des., 2015, 15 (2) ABSTRACT: The influence of the counteranion on the ability of the mesogenic cation 1-methyl-3-dodecyl-triazolium to form mesophases is explored. To that avail, salts of the cation with anions of different size, shape, and hydrogen bonding capability such as Cl −

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The reaction of benzyl 2-amino-4,6-O-benzylidene-2-deoxy-alpha-D-glucopyranoside (HL) with the metal salts Cu(ClO(4))(2)6 H(2)O and Ni(NO(3))(2)6 H(2)O affords via self-assembly a tetranuclear mu(4)-hydroxido bridged copper(II) complex [(mu(4)-OH)Cu(4)(L)(4)(MeOH)(3)(H(2)O)](ClO(4))(3) (1) and a trinuclear alcoholate bridged nickel(II) complex [Ni(3)(L)(5)(HL)]NO(3) (2), respectively. Both complexes crystallize in the acentric space group P2(1). The X-ray crystal structure reveals the rare (mu(4)-OH)Cu(4)O(4) core for complex 1 which is mu(2)-alcoholate bridged. The copper(II) ions possess a distorted square-pyramidal geometry with an [NO(4)] donor set. The core is stabilized by hydrogen bonding between the coordinating amino group of the glucose backbone and the benzylidene protected oxygen atom O4 of a neighboring {Cu(L)} fragment as hydrogen-bond acceptor. For complex 2 an [N(4)O(2)] donor set is observed at the nickel(II) ions with a distorted octahedral geometry. The trinuclear isosceles Ni(3) core is bridged by mu(3)-alcoholate O3 oxygen atoms of two glucose ligands. The two short edges are capped by mu(2)-alcoholate O3 oxygen atoms of the two ligands coordinated at the nickel(II) ion at the vertex of these two edges. Along the elongated edge of the triangle a strong hydrogen bond (244 pm) between the O3 oxygen atoms of ligands coordinating at the two relevant nickel(II) ions is observed. The coordinating amino groups of the these two glucose ligands are involved in additional hydrogen bonds with O4 oxygen atoms of adjacent ligands further stabilizing the trinuclear core. The carbohydrate backbones in all cases adopt the stable (4)C(1) chair conformation and exhibit the rare chitosan-like trans-2,3-chelation. Temperature dependent magnetic measurements indicate an overall antiferromagnetic behavior for complex 1 with J(1)=-260 and J(2)=-205 cm(-1) (g=2.122). Compound 2 is the first ferromagnetically coupled trinuclear nickel(II) complex with J(A)=16.4 and J(B)=11.0 cm(-1) (g(1,2)=2.183, g(3)=2.247). For the high-spin nickel(II) centers a zero-field splitting of D(1,2)=3.7 cm(-1) and D(3)=1.8 cm(-1) is observed. The S=3 ground state of complex 2 is consistent with magnetization measurements at low temperatures.

Two sets of new azobenzene-based bromide salts are synthesized, and their thermal photochromic properties are studied. Both sets are based on the imidazolium cation. The first set (1) features a symmetric biscation where two imidazolium head groups (Im) with different alkyl chains (Cn) are connected to a central azobenzene unit (Azo): [Azo(C1-Im-Cn) 2 ]; n = 6, 8, 10, 12, 14. The other one contains an n-alkylimidazolium cation (Cn-Im) bearing a terminal azobenzene unit (C1-Azo) substituted with an alkoxy chain (O-Cm) of either two (2) or six (3) carbon atoms: [C1-Azo-O-Cm-Im-Cn]; m = 2, n = 8, 10, 12 and m = 6, n = 8, 10, 12, 14, 16. For both cation classes, the influence of alkyl chains of varying length on the thermal phase behavior was investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). For five compounds (Azo(-C1-Im-C12) 2 (1d), Azo(-C1-Im-C12) 2 (1e), C1-Azo-O-C2-Im-C10 (2b), C1-Azo-O-C2-Im-C12 (2c), and C1-Azo-O-C6-Im-C16 (3e)), the formation of a liquid crystalline phase was observed. The biscationic salts (1) are all comparatively high melting organic salts (180-240 °C), and only the two representatives with long alkylchains (C12 and C14) exhibit liquid crystallinity. The monocationic salts with an O-C2 bridge (2) melt between 140 and 170 °C depending on the alkyl chain length, but from an alkyl chain of 10 and more carbon atoms on they form a smectic A liquid crystalline phase. The representatives of the third set with a O-C6 bridge qualify as ionic liquids with melting points less than 100 °C. However, only the representative with a hexadecyl chain forms a liquid crystalline phase. Representative single crystals for all sets of cations could be grown that allowed for single crystal structure analysis. Together with small-angle X-ray scattering experiments they allow for a more detailed understanding of the thermal properties. Through irradiation with UV-light (320-366 nm) all compounds undergo trans-cis isomerization, which reverses under visible light (440 nm). Disciplines Ceramic Materials | Complex Fluids | Other Materials Science and Engineering CommentsReprinted (adapted) with permission from Cryst. Growth Des., 2015, 15 (9) (2c), and C1-Azo-O-C6-Im-C16 (3e)), the formation of a liquid crystalline phase was observed. The biscationic salts (1) are all comparatively high melting organic salts (180−240°C), and only the two representatives with long alkylchains (C12 and C14) exhibit liquid crystallinity. The monocationic salts with an O−C2 bridge (2) melt between 140 and 170°C depending on the alkyl chain length, but from an alkyl chain of 10 and more carbon atoms on they form a smectic A liquid crystalline phase. The representatives of the third set with a O−C6 bridge qualify as ionic liquids with melting points less than 100°C. However, only the representative with a hexadecyl chain forms a liquid crystalline phase. Representative single crystals for all sets of cations could be grown that allowed for single crystal structure analysis. Together ...

A new framework cobalt(II) hydroxyl phosphate, Co 2 PO 4 OH, was prepared by ionothermal synthesis using 1-butyl-4-methyl-pyridinium hexafluorophosphate as the ionic liquid. As the formation of Co 2 PO 4 F competes in the synthesis, the synthesis conditions have to be judiciously chosen to obtain well-crystallized, single phase Co 2 PO 4 OH. Single-crystal X-ray diffraction analyses reveal Co 2 PO 4 OH crystallizes with space group I4 1 /amd (a = b = 5.2713 (7)