Sandwich-like

Alkyl derivatives such as 1,4-S6(NR)2 and S4(NR)4 can be synthesized by reacting S2CI2 with primary amines RNH2 in an inert solvent. Compounds such as 1,4-S2(NR)4 (R = —C02Et) are now also well characterized.The bis-adduct [Ag(S4N4H4)2]" " has been isolated as its perchlorate this has a sandwich-like structure and is unique in being S-bonded rather than N-bonded to the metal ion. ... 

Tin phthalocyanines can be prepared using tin(II)110 or -(IV)154 chlorides. The reaction can be performed in 1-chloro-1 10,1 37,1 55 or 1-bromonaphthalene,154 starting from phthalonitrile110137154,155 or phthalic anhydride. In the second case, urea and ammonium molyb-date(VI) arc added.137 The central tin atom can also be introduced into metal-free phthalocyanine by the reaction with tin(IV) chloride in dimethylformamide.141 Treatment of PcSnCl2 with disodium phthalocyanine in refluxing 1-chloronaphthalenc forms a sandwich-like bis-(phthalocyanine) Pc2Sn.154... 

Bismuth phthalocyanines of the type PcBiX can be prepared in solution by the reaction of bismuth(III) halides with PcLi2 or in a molten mixture of phthalonitrile and bismuth(III) halide.166 The sandwich-like complex [Pc2Bi]- can be obtained by slowly adding potassium methoxide to a melt of bismuth(III) oxonitrate and phthalonitrile.167... 

Lanthanides form phthalocyanines PcMX, sandwich-like complexes of the type Pc2M, and triple-decker complexes of the type Pc3M2. 

In the case of lanthanide elements, other sandwich-like compounds such as the triple-decker phthalocyanincs have been reported. Yttrium(III) acetate hexahydratc when treated with phthalonitrile at 230 C for 8 hours forms a triple-decker phthalocyanine.202... 

In the cation [Pb(15-crown-5)2]2+ the lead atom is sandwich-like coordinated by the ten oxygen atoms of the two crown ether molecules. (Figure 13). 

FIGURE 13. Structure of the sandwich-like cation [Pb(15-crown-5)2]2+. Reprinted from Reference 88 by permission of Barth Verslagsgesellschaft mbH... 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

Detection of pyrophosphate has also been demonstrated by a simple selfassembling system A-10 (Figure 10.32) with a pyrene-functionalized monoguani-dinium receptor. This receptor was found to self-assemble to form a 2 1 (host -guest) complex with high selectivity for biologically important pyrophosphate ions in methanol. A sandwich-like ground-state pyrene dimer is formed. The character-... 

Fig. 12.1 Main structural models of graphene-metal oxide hybrids, (a) Anchored model oxide particles are anchored to the graphene surface, (b) Encapsulated model oxide particles are encapsulated by graphene, (c) Sandwich-like model graphene is sandwiched between the metal oxide layers, (d) Layered model a structure composed of alternating layers of oxide nanoparticles and graphene, (e) Mixed model graphene and oxide particles are mechanically mixed and graphene sheets form a conductive network among the oxide particles. Red metal oxide Blue graphene. Reprinted with permission from [41]. Copyright 2012, Elsevier B.V.

Figure 5. Sandwich-like structural element proposed for the morphological organization of Nafion. (Reprinted with permission from ref 71. Copyright 2001 Elsevier.)...

Fig. 34 DFT calculation PHB formation in a cage of the dimeric Cr (salphen) sandwich-like structure [94] (reproduced with permission of Macomolecules94)...

These systems are based on immersion of two photoactive electrodes in an electrolyte solution with connection via an external circuit. An overall solar-spectrum hydrogen conversion efficiency of 0.25% was found at zero bias for the n-Ti02/p-GaP cell. Nozik further designed a new type of cell, so-called photochemical diodes that do not require external wires and functions without electrical bias [26]. This device [26], consisting of a small sandwich-like structure, Fig.7.2, such as Pt/n-GaP, and n-Ti02/p-GaP connected through ohmic contacts, when suspended in an appropriate electrolyte causes decomposition of water upon exposure to light. 

The crown ethers and the related cryptates (cryptates were first reported by J-M Lehn (J ) of France in 1969 (Figure 3)), have been used in a variety of synthetic procedures primarily because of their ability to solvate ionic materials in organic solvents (1, 14). Recently, it has been shown that crown ethers in the solid state form "sandwich" like complexes with most metals and that the counterion is also tightly bound (1 ). It is this evidence that suggested their use as ion traps in silicone RTV formulations. 

The bis-macrocyclic ring is positively charged because of the presence of Ni(II) and Cu(II). The crown ether and the bis-azamacrocyclic ring form a sandwich-like structure in such a way that one of the crown ether aromatic rings is located between the two metal-coordinated macrocyclic rings. The second aromatic ring is located almost parallel to the previous one outside the two linked macrocycles. 

The actual blotting process may be accomplished by one of two methods passive (or capillary) transfer and electroblotting. In passive transfer, the membrane is placed in direct contact with the polyacrylamide gel and organized in a sandwich-like arrangement consisting of (from bottom to top) filter paper soaked with transfer buffer, gel, membrane, and more filter paper. The sandwich is compressed by a heavy weight. Buffer passes by capillary ac-... 

On the other hand, the interest towards this field is accounted for by the possibility to create polymeric systems, combining the unique properties of low-molecular liquid crystals and high molecular compounds, making it feasible to produce films, fibers and coatings with extraordinary features. It is well-known that the utilization of low-molecular thermotropic liquid crystals requirs special hermetic protective shells (electrooptical cells, microcapsules etc.), which maintain their shape and protect LC compounds from external influences. In the case of thermotropic LC polymers there is no need for such sandwich-like constructions, because the properties of low-molecular liquid crystals and of polymeric body are combined in a single individual material. This reveals essentially new perspectives for their application. 

The area of metallocene chemistry started in 1952 with the successful synthesis of ferrocene177, Fe(C5H5)2, and with the description of a new type of bonding in this sandwich-like compound178,179. 

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