Structural Control and Chiroptical Response in Intrinsically Tetra- and Pentanuclear Chiral Gold Clusters

Controlling the synthesis of chiral metal clusters in the aspects of nuclearity number, metal–metal interaction, and spatial arrangement of metal atoms is crucial for establishing the correlation of detailed structural factors with chiroptical activity. Herein, a series of enantiopure gold complexes with nuclearity numbers ranging from 2 to 5 were constructed and structurally characterized. On the basis of the annulation reaction between two aurated μ2-imido nucleophilic units with various aldehydes, we finely adjusted the metal–metal interaction and torsion angles of a characteristic tetranuclear metal cluster by introducing different substituents into the resulting imidazolidine dianionic chiral skeleton. Further structural investigations, contrast experiments, and time-dependent density functional theory calculations confirmed that the chiroptical response of the acquired asymmetric metal clusters was mainly affected by the geometrically twisted arrangement of metal atoms. Finally, the tetranuclear gold cluster compound with the shortest intermetallic interaction and the largest torsion angle of a Au4 core showed the highest absorption anisotropy factor up to 2.2 × 10–3. In addition, the correlation of structural factors with the stability of chiral gold clusters was thoroughly evaluated by monitoring the CD, UV–vis, and NMR spectra at elevated temperatures. Insight into the relationship between the structural factors with the chiroptical property and stability of chiral gold clusters in this work will help us to design and achieve more stable chiral metal clusters and stimulate their practical applications in chiroptical functional materials

Direct Revelation of Multiple Conformations in RNA by Femtosecond Dynamics

RNA structures are intrinsically dynamic, and the dynamics are important for interactions and recognition. We developed a strategy using femtosecond dynamics to quantitatively investigate the heterogeneous nature of RNA structures. The different conformations that exist in an RNA molecule are resolved based on their distinct temporal behaviors of the fluorescent decays for the incorporated fluorophore on ultrafast time scales. Using this strategy, we have probed the GNRA tetraloop motif and revealed alternative structures that have not been directly observed by other techniques. A model is proposed for the coexisting multiple conformations and the conformational dynamics for this motif

Feature integration effects.

<p>Mean reaction times (RTs) and mean error rates as a function of the repetition versus alternation of response key/graphic shape and Stroop stimulus congruency level.</p

Synthesis of the Tetracyclic Core of the Kempanes by a Ring-Closing Metathesis Strategy

The synthesis of the tetracyclic ring system of the kempane diterpenes was achieved through the highly regio- and stereoselective Diels−Alder reaction of an isopropenyl-diene with 2,6-dimethyl-p-benzoquinone, addition of an allyl group, and ring-closing metathesis of the isopropenyl and allyl groups

Congruency sequence effects.

<p>Mean reaction times (RTs) and mean error rates for congruent and incongruent trials in the present trial (N) depending on the congruency of the previous trial (N−1).</p

Assembly of Silver(I) Two- and Three-Dimensional Coordination Networks with Complementary Tridentate Heteroaryl Ethynide Ligands

Three pairs of complementary nitrogen heteroaryl ligands [2,6-(CC)2-py and 2-CC-pym; 2,5-(CC)2-py and 2-CC-pyz; 3,5-(CC)2-py and 5-CC-pym (py = pyridine, pyz = pyrazine, pym = pyrimidine)], wherein a ring nitrogen atom in one is interchanged with a carbon atom bearing an ethynyl substituent in the other, have been used to generate seven silver(I) complexes (1−7), in which silver infinite chains and two-dimensional coordination networks bridged by heteroaryl ethynide ligands were obtained as pre-programmed. The relative positions and bonding preference between the ethynide group and ring nitrogen atom act as controlling factors to produce various structural building units for the formation of multidimensional coordination networks. The fusion of CC⊃Agn (n = 3, 4) building units yields multinuclear silver aggregates in 1−6 whose nuclearities range from seven to twelve. The crystal structure of 7 displays a honeycomb layer composed of Ag4 baskets alternately linked by pyrimidinyl-5-ethynide ligands. In addition, complex 1 features an infinite chain composed of an alternate arrangement of twist-boat water hexamers and bridging silver atoms

Silver(I)−Thiophene π Interaction in the Assembly of Coordination Networks with the Supramolecular Synthons R−C⋮C⊃Ag<i>_n</i> (R = 2- or 3-thienyl; <i>n</i> = 4)^†

Silver−thiophene π interactions in two bonding modes, namely, η2-(CC) and κ-(C,S), have been observed for the first time in crystalline silver(I) complexes (C4H3S-2)C⋮CAg·4AgCF3CO2 (1), 2[(C4H3S-2)C⋮CAg]·8AgCF3CO2·CH3CN (2), and (C4H3S-3)C⋮CAg·4AgCF3CO2 (4), bearing thiophene ligands with an ethynide substituent at the 2- or 3-position. Introduction of an additional betaine component in 3[(C4H3S-2)C⋮CAg]·8AgCF3CO2·Me3N+CH2CO2-·4.5H2O (3) and replacement of trifluoroacetate by pentafluoropropionate in (C4H3S-3)C⋮CAg·5AgC2F5CO2·4H2O (5) were found to interrupt these silver−thiophene π interactions and instead form an infinite π−π-stacked silver chain and a π−π-stacking-stabilized Ag8 aggregate, respectively. The establishment of a new kind of silver−ethynide supramolecular synthon, R−C⋮C⊃Agn (R = 2-, 3-thienyl; n = 4), highlights the potential of building metal−organic frameworks utilizing the π-coordination capacity of a heterocyclic ring

Assembly of Polymeric Silver(I) Complexes of Isomeric Phenylenediethynides with the Supramolecular Synthons Ag<i>_n</i>⊂ C₂RC₂ ⊃Ag<i>_n</i> (R = <i>p</i>-, <i>m</i>-, <i>o</i>-C₆H₄; <i>n</i> = 4, 5)

New Agn⊂ C2RC2 ⊃Agn (R = p-, m-, o-C6H4; n = 4, 5) supramolecular synthons have been explored in the coordination network assembly of silver(I) complexes of the isomeric phenylenediethynides. An unprecedented μ5-η-coordination mode for the ethynide moiety and a mixed μ4,μ5-coordination mode for the o-phenylenediethynide group are observed, providing a rationale for the abundant occurrence of C2@Agn (n ≤ 10) polyhedral cages in double and multiple salts of silver acetylenediide

Silver(I) 1,3-Butadiynediide and Two Related Silver(I) Double Salts Containing the C₄^2- Dianion

Ag2C4, the second silver carbide to be fully characterized, has been synthesized as a light-gray powder (contaminated with metallic silver) that is explosive at high temperature (130 °C) and sensitive to mechanical shock, rather like the well-known prototype Ag2C2. In the pair of hydrated double salts Ag2C4·6AgNO3·nH2O (n = 2, 3), the nearly linear, centrosymmetric 1,3-butadiyne-1,4-diyl dianion C42-exhibits an unprecedented μ8-coordination mode, each terminal being capped by four σ-bonded silver(I) atoms with π-interaction to one of them

Silver(I)−Thiophene π Interaction in the Assembly of Coordination Networks with the Supramolecular Synthons R−C⋮C⊃Ag<i>_n</i> (R = 2- or 3-thienyl; <i>n</i> = 4)^†

Silver−thiophene π interactions in two bonding modes, namely, η2-(CC) and κ-(C,S), have been observed for the first time in crystalline silver(I) complexes (C4H3S-2)C⋮CAg·4AgCF3CO2 (1), 2[(C4H3S-2)C⋮CAg]·8AgCF3CO2·CH3CN (2), and (C4H3S-3)C⋮CAg·4AgCF3CO2 (4), bearing thiophene ligands with an ethynide substituent at the 2- or 3-position. Introduction of an additional betaine component in 3[(C4H3S-2)C⋮CAg]·8AgCF3CO2·Me3N+CH2CO2-·4.5H2O (3) and replacement of trifluoroacetate by pentafluoropropionate in (C4H3S-3)C⋮CAg·5AgC2F5CO2·4H2O (5) were found to interrupt these silver−thiophene π interactions and instead form an infinite π−π-stacked silver chain and a π−π-stacking-stabilized Ag8 aggregate, respectively. The establishment of a new kind of silver−ethynide supramolecular synthon, R−C⋮C⊃Agn (R = 2-, 3-thienyl; n = 4), highlights the potential of building metal−organic frameworks utilizing the π-coordination capacity of a heterocyclic ring