The Coordination Behavior of Oxygen-depleted Calixarenes towards d10 Noble Metal Ions

A calix[4]arene, in which two of the phenol functions are replaced by pyrazole units, [H₂(bpzCal)], was investigated as a ligand for Cu⁺, Ag⁺ and Au⁺ ions. Using [Cu(MeCN)₄]BF₄ and AgSbF₆ as the precursors, complexes [MH₂(bpzCal)]X (M = Cu, X = BF_4; M = Ag, X = SbF₆) were formed, where the calixarene ligands adopt a 1,3-alternate structure and the metal ions are coordinated linearly by the two pyrazolyl donors. [CuH₂(bpzCal)]BF₄ displayed a – for copper(I) complexes – unusual stability towards O₂, which is due to the steric protection of the Cu^I center. By contrast a dinuclear copper(I) complex [Cu₂(bpzCal)] that was obtained through treatment of [H₂(bpzCal)] with two equivalents of Cu(HMDS) is rather sensitive towards O₂. The preparation of a gold complex required the employment of a gold precursor, which contains one labile and one stabilizing neutral ligand, namely [(PPh₃)Au(NCMe)]SbF₆, which led to the formation of [(PPh₃)AuH₂(bpzCal)]SbF₆. In this complex [H₂(bpzCal)] acts only as a monodentate ligand for the gold center. Taken together, the results demonstrate the potential of [H₂(bpzCal)] in providing rather different coordination spheres for metal ions.     

Verifiable conditions of <Emphasis Type="Italic">ℓ</Emphasis><Subscript>1</Subscript>-recovery for sparse signals with sign restrictions

We propose necessary and sufficient conditions for a sensing matrix to be “s-semigood” – to allow for exact ℓ ₁-recovery of sparse signals with at most s nonzero entries under sign restrictions on part of the entries. We express error bounds for imperfect ℓ ₁-recovery in terms of the characteristics underlying these conditions. These characteristics, although difficult to evaluate, lead to verifiable sufficient conditions for exact sparse ℓ ₁-recovery and thus efficiently computable upper bounds on those s for which a given sensing matrix is s-semigood. We examine the properties of proposed verifiable sufficient conditions, describe their limits of performance and provide numerical examples comparing them with other verifiable conditions from the literature.     

光学特异材料的设计(英文)

In this contribution we review our latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials(MMs) at will. We give three examples of metamaterial designs that have been realized by means of electron-beam lithography and whose spectroscopic characteristics have been comprehensively investigated. In every case, our experiments are complemented by rigorous numerical simulations. Particular emphasis is put on the significance of such tailored effectiv...     

Electronic Tuning of Host-Guest Interactions within the Cavities of Fluorophore-Appended Calix[4]arenes

A series of fluorescent calix[4]arene scaffolds bearing electron-rich carbazole moiety conjugated at the lower rim have been prepared. Studies of the fluorescence quenching in the presence of the N-methyl pyridinium guest revealed that the electronic properties of the distal phenolic ring play a major role in the host–guest complexation. In particular, placing an electron-donating piperidine fragment at that ring significantly increased the host–guest interactions, while introducing the same fragment into the proximal phenolic ring weakened the fluorescence response. These results suggest that the dominant interactions between the guest and calixarene cavity involve the oxygen-depleted fluorophore-bearing aromatic ring and not the more electron-rich unsubstituted phenolic fragments.