For inorganic chemists, the 1990s have brought a blossoming, both of a large field of ordered solid-state structure synthesis and a large number of words to describe it. Organized, functional nanostructures are made using supramolecular chemistry; molecular recognition guides selfassembly or self-organization; molecular patterning and templating are tools for directed synthesis."'21 All of these words reflect a desire, on the part of the chemist, to deliberately control, to design, the synthesis of a particular solid-state structure.In order to achieve the goals of advanced materials science which are to create materials for quantum electronics, nonlinear optics, photonics, chemoselective sensing, size-and shape-selective electrocatalysis and redox processes, among others, we wish to build-in function by controlling form. Within the field of crystalline, microporous "zeotype" materials, there has been a significant change reflected in the language used to describe the work. Natural and synthetic zeolites were discovered, where currently we design, or "create and invent""] novel open framework types. The diversity of non-oxide open-framework materials, that we "design" today are not materials "waiting to be discovered".The object of self-assembly is to put together a set of reagents, molecules, with matching functional groups and or templates, such that they are compelled to join together in a predefined way. This is, of course, easier said than done! The challenge, then, is to characterize and to predict the modes of formation of the desired materials, in this case crystalline, non-oxide, porous, inorganic and organometallic frameworks. The empirical approach has been to synthesize as many structures in as many systems with as many topologies as possible, in order to fully explore and understand all the tools at hand, and so to develop the skill to predefine the structure-property-function relationship.
Synthetic and X-ray structural details, optical and vibrational spectroscopic, and thermal properties of the materials [(CH 3 ) 4 N] 2 M 2 Ge 4 S 10 (where M ) Cu, Ag), are described for the first time. Rietveld PXRD full-profile structure refinements of [(CH 3 ) 4 N] 2 M 2 Ge 4 S 10 reveal a novel open-framework architecture in which dimetal M 2 2+ and adamantanoid Ge 4 S 10 4building blocks are alternately substituted into the tetrahedral Zn 2+ and S 2sites of a zinc blende lattice, all linked together by [Ge(µ-S)] 2 M-M[(µ-S)Ge] 2 metal-metal bonded bridging units. The metal-metal distances in the S 2 M-MS 2 "twisted I" dihedral unit are 2.761 Å (Ag) and 2.409 Å (Cu). These internuclear separations are shorter than the bulk metals themselves (2.89 Å, Ag; 2.54 Å, Cu). This implies that the adamantanoid Ge 4 S 10 4--based open-framework structure is held together by d 10 -d 10 M + -M + metal-metal bonds. FT-Raman provides a direct probe of this interaction. Dimetal-framework breathing vibrational modes are observed around 38 cm -1 for M ) Ag and 55 cm -1 for M ) Cu. In situ VT-PXRD analysis demonstrates that [(CH 3 ) 4 N] 2 Ag 2 Ge 4 S 10 retains its structural integrity upon exposure to air after in vacuo heating above the [(CH 3 ) 4 N] + loss temperature. It seems likely that the disilver connection of adamantanoid Ge 4 S 10 4building blocks confers thermal stability upon the framework.
Here we report on investigations that have revealed for the first time that the Cs ' ion templates the same metal germanium sulfide open-framework as (CH3),N+ (TMA+), and that metal complexing agents enhance crystal size by at least two orders of magnitude. The synthesis, structures and thermal properties of Cs,FeGe4Slo . x H20 and TMA2FeGe4Slo are also described. Both have 3D zinc blende-type open-framework structures. These materials have the same connectivity a s TMA2MnGe,Slo. The tetrahedral sites in the lattice are alternately substituted by pseudo-tetrahedral Fez+ and adamantanoid Ge&; building blocks, covalently linked together by Fe(p-S)Ge bridge bonds, to give a tetragonal unit cell. The charge-balance of the anionic framework [FeGe4S,o]2p is maintained by either Cst or TMA-ions in the cavity spaces. Synthesis of these materials demonstrates an interesting example of a self-assembly process in which a 3D framework is built from molecular precursors. Water adsorption-desorption cycling from room temperature to 200 "C reveals framework flexibility between larger and smaller tetragonal unit cell 14 isotypes. The compound TMA2FeGe,Slo is stable in nitrogen at 350°C and under vacuum at 450°C. The corresponding temperatures for Cs2FeGe,SIo are 530 "C and 630°C; it is stable on cooling to room temperature under vacuum, and after subsequent exposure to air. Six hundred thirty degrees Celsius is the highest recorded temperature a t which the integrity of a non-oxide framework has been maintained. The framework stability and flexibility of "all-inorganic" CszFeGe4Slo provides an encouraging example for researchers interested in developing sulfide-based framework materials with practical applications. The Cs+ and (CH3)4N+ (TMA+) templatc mediated synthesis, single crystal XRD structure deterinination and thermal properties of CszFeGe4Slo x H20 and TMA2FeGe4Slo are reported here for the first time. These materials have isostructural zinc blende-type iron, germanium, and sulfide open-frameworks; they exhbit impressive framework stability, and in the case of Cs2FeGe4Slo . x HZO, framework flexibility. In a procedure similar to that reported for TMA2MnGe4Slo, they were prepared by a two step reaction sequence [*]. Elemental Ge (99.99%). Aldrich) and S (99.999%, Aldrich), in stoichiometric amounts, were hydrothermally digested in a 5% excess of aqueous TMAOH or CsOH (H20/Ge = 50; 150°C, tumbled, 16 hours). From the resultant solution, TMA4Ge4Slo or Cs4Ge4Slo was precipitated by adding acetonelethanol. lf was then recovered by filtration or centrifugation, and purified and characterized (pXRD, Ranan). Monoclinic salts of Cs4Ge4Slo . 3 HZO and Cs4Ge4Slo . 4 H 2 0 were previously reported, along with their vibrational ~pectra['~,'~]. Yields of greater than 95% were readily achieved for the TMA4Ge4Slo material with greater than 99.99% purity [']. Use of TMA4Ge4Slo or Cs4Ge4Sio as synthetic precursors avoided inhomogeneous and insoluble GeS2, which can often contain impurities deleterious to the crystallization of metal cha...
The synthesis, adsorption and catalytic properties of a new family of crystalline nanoporous tin(1v) chalcogenides, first reported in 1989 by Bedard and co-workers in two U. S. patents,"] opened the field of nanoporous non-oxide materials with a group of materials denoted R-SnS-n, where R denotes a tetraalkylammonium template and n refers to different structure types. As structural information became available, these materials, made of the components of bulk semiconductors, were recognized not only as potential forms of porous semiconductors, but also as the topological complement of semiconductor nanocluster arrays. ['-51 Porous semiconductors and their electronic and optical properties are of considerable current interest in the semiconductor physics literature, as exemplified by luminescent forms of porous siliconr6] and quantum antidot lattices.r71 Many authors have recently taken interest in the idea of nanoporous semiconductorsls-lO] and expanded it into other semiconductor systems.Our research has taken on the pursuit of Bedard's nanoporous tin(1v) sulfides and has recently added many more structural examples, including isostructural tin(1v) selenides. The structures of many of these materials have been obtained through single-crystal and powder X-ray diffraction."'.The synthesis and characterization of a series of tunable composition isostructural nanoporous thioselenide materials has been reported.["] Atomic force microscopy (AFM) has been utilized to provide molecular-resolution images of the crystal surfaces of some of these material^.^'^] Also the thermochemical properties of some of these materials have been studied through variable-temperature powder X-ray diffraction and thermogravimetric analysis-linked mass ~pectrometry.['~] Throughout our studies much has been learned about the mode of formation of these materials and the chemistry behind these ~yntheses.~ '~] In this paper, we begin to explore the remarkable flexibility of some of these structures. This flexibility can result in polytypism making structural characterization a challenge, but it also confers a responsiveness to the materials which makes them extraordinary. These materials can respond to changes of organic template type and loading, or the adsorption and desorption of guest molecules, often with measurable deformations of their open-framework structures, alterations in unit cell dimensions and space group, with accompanying changes in their optical absorption properties. This unusual phenomenon suggests that this class of materials offers new opportunities and potential for chemical sensing.A noteworthy structural feature that we have discovered in the R-SnX-1 (R,Sn,S,, R,Sn,Se,) and R-SnS-3 (R,Sn,S,) nanoporous tin(1v) chalcogenides is the unique ability of their open-frameworks to undergo elastic deformations in response to variation of the organic template or imbibed molecular guests. For example, we have learned that R-SnS-1 isostructures can be synthesized with occluded NHf, Me,N@, Et,N@, "Pr,NH@, QHO, 'BuNHf and DABCOHO ...
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