Reticular synthesis and the design of new materials

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62718/1/nature01650.pd

Negative thermal expansion and low-frequency modes in cyanide-bridged framework materials

We analyze the intrinsic geometric flexibility of framework structures incorporating linear metal-cyanide-metal (M-CN- M′) linkages using a reciprocal-space dynamical matrix approach. We find that this structural motif is capable of imparting a significant negative thermal expansion (NTE) effect upon such materials. In particular, we show that the topologies of a number of simple cyanide-containing framework materials support a very large number of low-energy rigid-unit phonon modes, all of which give rise to NTE behavior. We support our analysis by presenting experimental verification of this behavior in the family of compounds Znx Cd1-x (CN)2, which we show to exhibit a NTE effect over the temperature range 25-375 K more than double that of materials such as Zr W2 O8. © 2005 The American Physical Society

Guest-dependent negative thermal expansion in nanoporous Prussian Blue analogues (MPtIV)-Pt-II(CN)(6)center dot x{H2O} (0 <= x <= 2; M = Zn, Cd)

The guest-dependent thermal expansion behavior of the nanoporous Prussian Blue analogues MIIPtIV(CN)6.x{H2O} (0 </= x </= 2; M = Zn, Cd) has been investigated using variable temperature single-crystal X-ray diffraction. The dehydrated phases MIIPtIV(CN)6 were found to exhibit negative thermal expansion, attributed to thermal population of low energy transverse vibrations of the bridging cyanide ligands. The presence of guest molecules within the framework pore system was found capable of dampening the effect of these transverse vibrational modes. The guest-loaded ZnII phase, in which the available pore volume is commensurate with the volume occupied by individual water molecules, possesses a considerably higher coefficient of thermal expansion, with the material switching from positive to negative thermal expansion behavior upon guest removal

Thermal expansion matching via framework flexibility in zinc dicyanometallates.

The thermal expansion properties of two isostructural zinc dicyanometallates that crystallize with and without the inclusion of a weakly interacting secondary crystalline phase have been investigated using variable temperature single-crystal and powder X-ray diffraction. The guest-free Zn[Au(CN)(2)](2) framework was found to show very strong anisotropic positive and negative thermal expansion. In contrast, its cocrystal analogue Zn[Ag(CN)(2)](2) x xAgCN exhibited much more moderate behavior, such that the coefficient of thermal expansion for the host Zn[M(CN)(2)](2) framework now matched that of crystalline AgCN. It was proposed that this correlation points to a more general ability of highly flexible framework materials to "match" the thermal expansivity of adhered phases (e.g., substrates, sorbates, or cocrystallized species), suggesting a methodology of eliminating thermal strain in multicomponent assemblies

Flexible sorption and transformation behaviour in a microporous metal-organic framework

Crystals of the metal-organic framework material Ni2(4,4‘-bipyridine)3(NO3)4 (A) have been grown by reaction of Ni(NO3)2·6H2O and 4,4‘-bipyridine in methanol solution. Single-crystal X-ray diffraction experiments show that the ladder structure of the framework is maintained after desolvation of the material, resulting in the production of a porous solid stable to 215(4) °C. Powder X-ray diffraction has been employed to confirm the bulk purity and temperature stability of this material. The crystal structure indicates that the pore window has an area of 12.3 Å2. However, sorption experiments show these windows will admit toluene, which has a minimum cross-sectional area of 26.6 Å2, with no significant change in the structure. Monte Carlo docking calculations show that toluene can be accommodated within the large pores of the structure. Exposure of the related microporous material Ni2(4,4‘-bipyridine)3(NO3)4·2C2H5OH (B) to methanol vapor causes a guest-driven solid-state transformation to A which is observed using powder X-ray diffraction. This structural rearrangement proceeds directly from crystalline B to crystalline A and is complete in less than 1 day. Mechanisms for the transformation are proposed which require breaking of at least one in six of the covalent bonds that confer rigidity on the framework