Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties

The research into adamantane-type compounds has gained momentum in recent years, yielding remarkable new applications for this class of materials. In particular, organic adamantane derivatives (AdR4) or inorganic adamantane-type compounds of the general formula [(RT)4E6] (R: organic substituent; T: group 14 atom C, Si, Ge, Sn; E: chalcogenide atom S, Se, Te, or CH2) were shown to exhibit strong nonlinear optical (NLO) properties, either second-harmonic generation (SHG) or an unprecedented type of highly-directed white-light generation (WLG) - depending on their respective crystalline or amorphous nature. The (missing) crystallinity, as well as the maximum wavelengths of the optical transitions, are controlled by the clusters' elemental composition and by the nature of the organic groups R. Very recently, it has been additionally shown that cluster cores with increased inhomogeneity, like the one in compounds [RSi{CH2Sn(E)R'}3], not only affect the chemical properties, such as increased robustness and reversible melting behaviour, but that such 'cluster glasses' form a conceptually new basis for their use in light conversion devices. These findings are likely only the tip of the iceberg, as beside elemental combinations including group 14 and group 16 elements, many more adamantane-type clusters (on the one hand) and related architectures representing extensions of adamantane-type clusters (on the other hand) are known, but have not yet been addressed in terms of their opto-electronic properties. In this review, we therefore present a survey of all known classes of adanmantane-type compounds and their respective synthetic access as well as their optical properties, if reported.

Electrochemically prepared oxygen and sulfur co-doped graphitic carbon nitride quantum dots for fluorescence determination of copper and silver ions and biothiols

Although great advances have been achieved in synthesis of fluorescent graphitic carbon nitride quantum dots (g-C₃N₄-dots), it is still challenging to develop g-C₃N₄-dots with high fluorescence quantum yield (FLQY) and multiple sensing functionalities. Herein, the oxygen and sulfur co-doped graphitic carbon nitride quantum dots (OS-g-C₃N₄-dots) with high FLQY of 33.9% were firstly synthesized by a simple electrochemical "tailoring" process. It was found that OS-g-C₃N₄-dots could specifically bind copper ions (Cu²⁺) and silver ions (Ag⁺), accompanied with a dramatic "turn-off" fluorescence response. With the help of different masking agents, OS-g-C₃N₄-dots are able to selectively detect Cu²⁺ and Ag⁺. Furthermore, the generated OS-g-C₃N₄-dots/Ag⁺ displayed a "turn-on" fluorescent response specific to biothiols (HCy, Cys and GSH). Therefore, the multiple functional sensing platforms based on "ON-OFF-ON" fluorescence response of OS-g-C₃N₄-dots for the detection of Cu²⁺, Ag⁺ and biothiols were constructed. Under the optimal conditions, the detection limits of Cu²⁺, Ag⁺, HCy, Cys and GSH were as low as 7.0 × 10^-10 M, 2.0 × 10^-9 M, 1.0 × 10^-8 M, 1.0 × 10^-8 M and 8.4 × 10^-9 M, respectively. Moreover, the prepared platforms could be successfully applied to the determination of Cu²⁺, Ag⁺ and biothiols in practical samples and exhibited excellent sensitivity and selectivity.

Zwitterionic Metalates of Group 11 Elements and Their Use as Metalloligands for the Assembly of Multizwitterionic Clusters

Reaction of RNHC(S)PPh2NPPh2C(S)NR (HRSNS; R = Me, Et) with M(I) (M = Cu, Ag, Au) salts afforded zwitterionic complexes of the general formula [M(RSNS)] (M = Cu, Ag, Au). The ligand was found in the solid state in S,S-kappa2 and S,N,S-kappa3 coordination fashions. [Cu(RSNS)] and [Ag(RSNS)] can be used as metalloligand building blocks for the assembly of pentanuclear multizwitterionic Cu5, Cu3Ag2 and Ag5 core clusters of the general formula [M'2{M(RSNS)}3]2+ (M = Cu, M' = Cu, Ag; M = M' = Ag) upon reaction with suitable M' salts. The crystal structures of the most significant compounds are reported herein. Compound [Ag2{Ag(RSNS)}2(OTf)2] was also isolated and structurally characterized, representing a model for the intermediate species of the aforementioned assembly.

M-S vibrational study in three-coordinate thiolato compounds (NEt4)2[M(SC6H4-p-X)3] and (NEt4)

By using p-substituted benzenethiolate ligands, the novel three-coordinate copper(I) and silver(I) thiolato complexes (NEt4)2[Cu(SC6H4-p-X)3] (X=Cl (1) and Br (2)), (NEt4)2[Ag(SC6H4-p-X)3] (X=Cl (3) and Br (4)) and novel clusters (NEt4)2[M4(mu-SC6H4-p-Cl)6] (M=Cu (5) and Ag(6)) have been prepared and structurally characterized by single crystal X-ray diffraction. All the complexes have three-coordinate sites having point-group D3h symmetry. The three-coordinate mononuclear silver(I) complexes 3 and 4 are the first examples. The M-S stretching bands were determined by far-IR and FT-Raman spectroscopies; nu(Cu-S) 363-372 cm(-1) and nu(Ag-S) 353-363 cm(-1). These results indicate that M-S stretching vibration energy in the three-coordinate metal(I) site of the mononuclear compounds or clusters is around 340-380 cm(-1), and it is a useful tool for determining their coordination modes.

Surface Enhanced Raman Spectroscopic Study of Isomeric Methylthiophenes in Silver Colloid

Surface Enhanced Raman Spectra (SERS) of 2-methylthiophene (2-MT) and 3-methylthiophene (3-MT) in silver colloid are compared with their normal Raman spectra in the bulk and in acetonitrile solution. Experimental results indicate that both the methylthiophene molecules are adsorbed on a metal surface through the sulfur atom. Assuming the image dipole theory to be valid, the observed surface enhancement factor of the C-H stretching mode in 2-MT indicates that the C-H bond of this isomer makes an angle of 51 degrees with the surface normal. The experimental results further suggest that the 3-MT molecule is adsorbed with its ring plane almost vertical to the metal surface; the 2-MT molecule, on the other hand, is tilted more than 45 degrees to the surface normal. The concentration dependence of the relative enhancement factor indicates that a monomolecular layer is formed on the metal surface at a specific concentration of the methylthiophenes in silver sol. No oligomerization of the two methylthiophenes on the silver surface is observed. Copyright 1999 Academic Press.

Surface-Enhanced Raman Spectroscopic Study of Isomeric Formylthiophenes in Silver Colloid

Surface enhanced Raman (SER) spectra of 2- and 3-formylthiophenes (2FT and 3FT) in silver colloids are compared with their normal Raman spectra in bulk and in acetonitrile solution. Experimental results indicate adsorption of 2FT on metal surface through the sulfur and the oxygen atoms with the ring plane vertical to the metal surface, whereas the ring plane of the 3FT molecule is inclined to the surface. Moreover, the SER spectrum of 2FT molecule predicts the existence of syn-form of this molecule in the adsorbed state because of large enhancement of the carbonyl stretching mode. Concentration dependence of relative enhancement infers the monolayer formation on metal surface at a specific concentration, implying strong evidence of chemisorption of the adsorbates. The excitation profile of C identical withC symmetric stretching mode of 2FT suggests classical plasmon resonance as the main contributor to surface enhancement. Copyright 1997 Academic Press. Copyright 1997Academic Press