Topological rearrangement within a single crystal from a honeycomb cadmium cyanide [Cd(CN)2]n 3D net to a diamond net

Complex Phase Behaviour and Structural Transformations of Metal-Organic Frameworks with Mixed Rigid and Flexible Bridging Ligands

Two new heteroleptic metal-organic framework materials show strong adsorption of H₂ and ethanol. [Co₂ (L1)(bdc)₂ ], where L1=N¹ ,N⁴ -bis(4-pyridinylmethyl)-2,5-dimethylbenzene-1,4-diamine and bdc is benzene-1,4-dicarboxylate, has a twofold interpenetrating pillared layer structure with pcu topology. It has a stepped, hysteretic EtOH adsorption that can be related to complicated phase and structural transformation behaviour that occurs on de-solvation and re-solvation, including major conformational changes to the geometry of the flexible L1 ligand. [Co₂ (L1)(bpdc)₂ ], where bpdc=biphenyl-4,4'-dicarboxylate, has a unique six-connected self-catenating framework structure. Solvation changes occur without significant structural change and a partially-hydrolysed material binds its own decomposition products as guests.

Rational construction of functional molybdenum (tungsten)–copper–sulfur coordination oligomers and polymers from preformed cluster precursors

Discrete Mo(W)–Cu–S clusters are used as precursors and building blocks for a diverse array of cluster-supported coordination oligomers and polymers.

New structure, reconstruction, and behaviour of the coordination polymer framework [CuZn(CN)4]– towards hydrated alkali metal ions

A new framework structure of the coordination polymer [CuZn(CN)4]– has been discovered in the newly synthesized [Na(H2O)n][CuZn(CN)4] (n = 12.7; 1). X-ray crystal structure analysis revealed a 3D framework comprised of tetrahedral Cu(I) and Zn(II) centres with bridging cyanide ligands containing both octagonal and square channel cavities; these channels contain hydrated Na+ ions as guests. In open air, complex 1 is extremely unstable and loses water molecules to form [Na(H2O)n][CuZn(CN)4] (n = 5.2–6.8; 2) within 30 min. Powder X-ray diffraction patterns showed that this change results in the conversion of the framework of complex 1 to the same framework observed in [K(H2O)n][CuZn(CN)4]. The [CuZn(CN)4]– framework of [K(H2O)n][CuZn(CN)4] has a tridymite structure with hexagonal channel cavities occupied by hydrated K+ ions. Like 1, 2 is also unstable under atmospheric conditions, yielding [Na(H2O)n][CuZn(CN)4] (n = 3), which has an unknown structure. While the framework of [K(H2O)n][CuZn(CN)4] is structurally flexible and robust, the framework of 2 is unstable and fragile. This contrast comes from the difference between the nature of the hydrated K+ and Na+ ions present in the frameworks.

Controlling the flexibility and single-crystal to single-crystal interpenetration reconstitution of metal–organic frameworks

By controlling the guest accessibility to open metal sites, MOFs can select interpenetration reconstitution or not.

Metal Exchange within a Body-Centred Cubic Hydrogen-Bonded Network

A hydrogen bonded network of composition Zn8(C4O7)4(H2O)12·hydrate was shown to undergo a single crystal to single crystal exchange process when crystals are immersed in a concentrated aqueous solution of Ni(ii). In the exchange process, half of the zinc(ii) centres are replaced by nickel(ii) centres. The process of metal ion exchange was monitored using IR spectroscopy. Crystal structures of the transformed crystal and the product generated from a direct synthetic approach are presented.

Stereoselective One-Pot Synthesis of Constrained N,O-Orthogonally Protected C-Glycosyl Norstatines [C(1‘)-Aminoglycosyl-1,3-dioxolan-4-ones]

A procedure for the synthesis of conformationally constrained C-glycosyl norstatines has been developed. The key step of the reaction is the addition of (S)-N-sulfinyl azomethines to chiral (2S)-enolates of dioxolanones which exploits Seebach's "SRS" principle. The trisubstituted C-glycosyl-alpha-hydroxy-beta-amino acids are formed as N,O-orthogonally protected 1'-glycosyl-sulfinylamino-dioxolan-4-ones, usually with high diastereomeric excesses. Both the sulfinyl group at the nitrogen atom and the acetal moiety of the dioxolanone ring were selectively removed, thus demonstrating the orthogonality of the two protecting groups. In fact, the MeO(-) induced methanolysis of the acetal group gave the corresponding methyl C-glycosyl-sulfinylamino-isoserinates, while the acid induced removal of the sulfinyl group gave the Nu-deprotected 1'-glycosylamino-dioxolan-4-ones, which were in several cases subjected to a one-pot base-induced cyclization yielding the corresponding glycosyl-beta-lactams. This allowed the stereochemical configuration assessment of the parent 1'-glycosyl-sulfinylamino-dioxolan-4-ones by chemical correlation methods or by NOE experiments performed on the beta-lactams.

Single Crystal to Single Crystal Structural Transformations in Molecular Framework Materials

The rapid advance in the synthesis and characterization of molecular frameworks over the past decade has opened an entirely new approach for the generation of nanoporous materials. With this advance has come an increasingly pressing need for the development of new techniques to characterize the guest-dependent structures of these novel and highly complex materials. In this review we highlight some of the relatively rare cases where single crystal diffraction has been used to characterize the flexible structures of molecular frameworks through the investigation of single crystal to single crystal (SC-SC) transformations.

Recent Advances in the Dynamics of Single Crystal to Single Crystal Transformations in Metal–Organic Open Frameworks

Single crystal to single crystal transformations have been the subject of growing interest in recent years. In this article, several examples of single crystal to single crystal transformations that occur in metal–organic open frameworks (MOFs) upon guest removal and rebinding, guest exchange, and chemical oxidation are introduced. Depending on the structures of the MOFs, host framework structures can be retained or altered upon guest removal. When host framework structures are altered, significant rearrangements of the molecular components, which involve sponge-like shrinkage/swelling, sliding, swing, bending, and/or rotational motions, occurs throughout the entire crystal to retain the single crystallinity.

Transformation of a Metal−Organic Framework from the NbO to PtS Net

Two metal-organic frameworks (MOFs), MOF-501 and MOF-502, respectively, formulated as Co(2)(BPTC)(H(2)O)(5).G(x) and Co(2)(BPTC)(H(2)O)(DMF)(2).G(x) (BPTC = 3,3',5,5'-biphenyltetracarboxylate; G = guest molecules), have been synthesized and structurally characterized, and their topologies were found to be based on the NbO (MOF-501) and PtS (MOF-502) nets. Heating MOF-501 in solution results in the more thermodynamically favored MOF-502.

Silver(I) Arylsulfonates: A Systematic Study of “Softer” Hybrid Inorganic−Organic Solids

The present study represents the first systematic examination of the effects on the layered structure of simple silver aryl-monosulfonates as the breadth of the pendant aryl group is increased beyond that where a simple "phosphonate-like" motif is sustainable. Five new silver arenesulfonates are reported. On the basis of comparison with Ag benzenesulfonate, a threshold of approximately 6.4 A is proposed and confirmed as the critical breadth of an aryl group for a simple layered motif to be observed in silver sulfonates. Ag 1,1'-biphenyl-4-sulfonate (1) and Ag 2-naphthalenesulfonate (2) are below this threshold and so form simple layered networks, termed type 1 solids. When the pendant group is broadened to a 1-naphthyl group, the layer incorporates coordinated water to maintain a layered structure giving Ag 1-naphthalenesulfonate hemihydrate (3a). This more diffuse structure is termed a type 2 solid. For anhydrous Ag 1-naphthalenesulfonate (3) and Ag 1-pyrenesulfonate (4), the additional breadth is compensated for by the formation of Ag-pi interactions and the formation of type 3 solids. Interactions between the pendant groups are observed to play a significant role in the packing of the solid. All frameworks are characterized by single crystal and powder X-ray diffraction, IR, DSC-TGA, and elemental analysis. The significance of this adaptable framework is discussed along with implications for design of stacked arene arrays.

Honeycomb Nets with Interpenetrating Frameworks Involving Iminodiacetato−Copper(II) Blocks and Bipyridine Spacers: Syntheses, Characterization, and Magnetic Studies

Three coordination polymers of copper(II), viz. ([Cu(ida)(4,4'-bipyH)]ClO(4))( proportional, variant ) (1), ([Cu(2)(ida)(2)(micro-4,4'-bipy)].2H(2)O)( proportional, variant ) (2), and [Cu(2)(ida)(2)(bpa)]( proportional, variant ) (3) have been synthesized by the process of self-assembly using Cu(ida) [ida = iminodiacetate(2-)] as the building block and 4,4'-bipyridyl and 1,2-bis(4-pyridyl)ethane (bpa) as linkers. Crystals of 1 are orthorhombic, of space group Pna2(1), with a = 13.8956(12) A, b = 16.3362(16) A, c = 7.3340(12), and Z = 4. Both compounds 2 and 3 crystallize in monoclinic space group P2(1)/a with a = 10.1887(8) A (9.6779(10) A for 3), b = 8.0008(11) A (9.1718(10) A), c = 11.6684(9) A (12.9144(12) A), beta = 98.307(11) degrees (102.796(18) degrees ), and Z = 2 (2). Compound 1 has a zigzag chain structure with an extensive hydrogen-bonded network while compounds 2 and 3 are honeycomb (6,3) nets with interpenetrating structures. Variable temperature (2-300 K) magnetic study indicates the presence of weak antiferromagnetic interactions (J = 0.82 +/- 0.01 cm(-)(1)) in 1 and ferromagnetic in 2 (J = -0.45 +/- 0.05 cm(-)(1)) and 3 (J = -0.21 +/- 0.02 cm(-)(1)). The extent of planarity of the bridging "Cu-O-C-O-Cu" moiety, acting as the super-exchange pathway between the neighboring copper centers, probably controls the sign of the magnetic exchange coupling in these compounds.

Crystal-to-crystal transformations of a microporous metal–organic laminated framework triggered by guest exchange, dehydration and readsorption

Single crystals of a neutral, microporous, laminated metal-organic framework (MOF)[Fe(pydc)(4,4'-bipy)]xH(2)O (1xH(2)O)(H(2)pydc = 2,5-dicarboxypyridine, 4,4'-bipy = 4,4'-bipyridine) were generated by hydrothermal synthesis, and its crystal structure was determined. 1xH(2)O retains the framework robustness to ca. 370 degrees C and is insoluble in common organic solvents. By soaking in MeOH and EtOH solutions, 1xH(2)O was transformed directly from the parent single crystals into single crystals of 1xMeOH or 1xEtOH, respectively. Meanwhile, 1xH(2)O shrank to the guest-free framework (h) or (v), respectively, under appropriate heating (up to 160 degrees C in N(2)) or vacuum treatment (10 mmHg) at room temperature. Compared to that of 1xH(2)O, the unit-cell volume of 1xEtOH slightly increases by 2.9%, whereas those of (h) or (v) are reduced by 8.2 and 6.6%, respectively. The anhydrous (v) was found to be highly chemically reactive, taking up ethanol vapor to furnish the solvated crystal structure of an 'expanded' framework 1xEtOH. In a mixture of ethanol-DMF or ethanol-benzene, a selective exchange process was observed, with only ethanol molecules exchanged into the structure due to the limited free size of the channels in the framework of. All the transformed crystals have also been characterized by X-ray single-crystal diffraction to understand the crystal-to-crystal transformation, which have different free volumes (6.5-20.4%).

Organic-organometallic crystal engineering: novel formation of a honeycomb supramolecular architecture of [Re2(mu-OMe)3(CO)6]- anions encapsulating a linear H-bonded chain of [DABCO-H]+ cations

The title salt [Re(2)(mu-OMe)(3)(CO)(6)](-)[DABCO-H](+) (1) was prepared as colorless prismatic crystals by the reaction of DABCO with Re(CO)(5)(OTf) in refluxing methanol solution and was characterized by spectroscopic means including single-crystal X-ray diffraction techniques. The molecular structure of 1 revealed that a novel honeycomb supramolecular architecture of the anionic organometallic complex created a cavity with an effective diameter of 7.450(3) A that houses a linear H-bonded chain of [DABCO-H](+) in its center. This structure also represents the first example of the use of a linear chain of [DABCO-H](+) species as a countercation for a coordination compound.

Synthesis of a C-glycoside analogue of beta-D-galactosylthreonine

A C-linked analogue of beta-D-galactosylthreonine has been prepared from 2,3,4,6-tetra-O-benzyl-D-galactopyranolactone (1) in 14 steps. Three stereogenic centers were created during the synthesis, with the anomeric center of the C-glycoside being generated first by addition of a Grignard reagent to 1 and subsequent reduction of the intermediate hemiacetal with triethylsilane. The two stereogenic centers in the threonine moiety were both established by alkylation of Evans' chiral N-acyloxazolidinone enolates.

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

Crystals of the metal-organic framework material Ni(2)(4,4'-bipyridine)(3)(NO(3))(4) (A) have been grown by reaction of Ni(NO(3))(2).6H(2)O 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) degrees 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 A(2). However, sorption experiments show these windows will admit toluene, which has a minimum cross-sectional area of 26.6 A(2), 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 Ni(2)(4,4'-bipyridine)(3)(NO(3))(4).2C(2)H(5)OH (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.

Design and synthesis of a novel class of sugar-peptide hybrids: C-linked glyco beta-amino acids through a stereoselective "acetate" Mannich reaction as the key strategic element

A new type of sugar-amino acid hybrid, which is comprised of a sugar unit (gluco-, galacto-, or mannopyranose) linked through a C-glycosidic linkage to the beta-position of an alpha-unsubstituted beta-amino acid unit, is presented. It is hypothesized that these new compounds, or the oligomeric peptides derived therefrom, might possess the structural features of beta-amino acid oligomers and the chemical and enzymatic resistance of C-glycosides to hydrolysis. The synthetic strategy is based on a new Mannich-type reaction between a chiral acetate enolate equivalent and alpha-amido sulfones derived from the corresponding sugar-C-glycoside aldehydes. While the sugar-C-glycoside aldehyde partner is prepared from well-established transformations on known sugar precursors, the lithium enolate derived from (1R)-endo-2-acetylisoborneol 3 is employed as the key element. This Mannich approach proceeds with essentially perfect diasteromeric control leading to the new beta-amino carbonyl adducts in good yields. Further, cleavage of the camphor auxiliary is smoothly performed by oxidative treatment with ammonium cerium nitrate (CAN). Complementarily, direct peptide-type coupling of the beta-amino carbonyl Mannich adducts with an alpha- or beta-amino acid residue and subsequent CAN-promoted detachment of the auxiliary yields dipeptide fragments bearing a sugar-containing aliphatic side chain and is a process that can be iterated. A preliminary conformational study based on the combination of experimental NMR data and molecular mechanics and molecular dynamics (MD) of one particular adduct is also provided.

Amphiphilic anionic analogues of galactosylceramide: synthesis, anti-HIV-1 activity, and gp120 binding

We describe the synthesis together with the results of anti-HIV-1 activity and gp120-monolayer binding experiments of new galactosyl amphiphiles, analogues of galactosylceramide, an alternative receptor used by HIV to infect CD4 negative cells. These compounds consist of single- and double-chain amphiphiles containing one or two galactose residues. To favor their clustering into galactosyl-rich microdomains, their molecular structure contains also an amino group or several hydroxyls or anionic groups, such as carboxylate, sulfate, sulfonate, and phosphate. Among the 12 new galactosylated compounds reported, a specific anti-HIV activity, although moderate (IC(50) from 10 to 50 microM), was detected only for three of them, i.e., I-GalSer[CO2Na][C14], II-GalSer[C14][C7SO3Na], and II-GalSer[C2SO4Na][C14], which contain an anionic group. The marked increase of surface pressure which was observed upon addition of gp120 into the aqueous subphase underneath the monolayers containing these galactolipids indicated gp120 insertion into the monolayers, suggesting that binding of these three derivatives to HIV-1 gp120 may be responsible for their anti-HIV activity.

Synthesis of beta-D-Galactosyl Ceramide Methylene Isostere

The methylene isostere of the glycosphingolipid beta-D-galactosyl N-palmitoyl C(18) ceramide has been synthesized by a linear reaction sequence starting from a beta-linked D-galactopyranosyl aldehyde. First, this sugar aldehyde was converted into a methylenephosphorane which in turn was coupled with N-Boc serinal acetonide. The double bond of the resulting olefin was reduced and the oxazolidine ring was cleaved and oxidized to give a C-glycosyl N-Boc alpha-amino butanal (three-carbon chain elongation). Then, an additional C(15) carbon chain was installed by addition of lithium 1-pentadecyne to the above glycosyl amino aldehyde. The syn/anti ratio (70:30) of the resulting mixture of amino alcohols was reversed (5:95) by an oxidation-reduction sequence to achieve the same stereochemistry as in the hydrophilic head of D-erythro-sphingosines. The major product was subjected to the reduction of the triple bond with LiAlH(4) to give the olefin with E geometry. Finally the N-amide group was installed by reaction with palmitoyl chloride and the O-benzyl protective groups of the sugar moiety were removed by treatment with lithium in liquid NH(3)-THF. The final product was characterized as the O-acetyl derivative.

Covalent Three-Dimensional Titanium(IV)-Aryloxide Networks

Ti((i)OPr)(4) was treated with 2.58 equiv of hydroquinone in THF to yield a red-orange powder formulated as [Ti(OC(6)H(4)O)(a)()(OC(6)H(4)OH)(3.34)(-)(1.83)(a)()(O(i)Pr)(0.66)(-)(0.17)(a)() (THF)(0.2)](n)() (1, (0.91 </= a </= 1.82)) based upon D(2)O/DCl quenching studies. Treatment of 1 with an excess of hydroquinone in Et(2)O or DME afforded burgundy [Ti(2)(&mgr;(1,4)-OC(6)H(4)O)(2)(&mgr;(1,4)-OC(6)H(4)OH)(2)(&mgr;-OC(6)H(4)OH)(2)](infinity) (2). Burgundy [Ti(2)(&mgr;(1,4)-OC(6)H(4)O)(2)(&mgr;(1,4):eta(2),eta(1)-OC(6)H(4)O)(2)(OH(2))(2).(H(2)O)(2).(H-OC(6)H(4)OH).(MeCN)](infinity) (4) was prepared from 1 and excess wet hydroquinone in CH(3)CN. The acetonitrile in 4 can be exchanged for THF or DME. Treatment of Ti(O(i)Pr)(4) with approximately 4 equiv of 2,7-dihydroxynaphthalene in Et(2)O at 100 degrees C (2 days) in a sealed tube yielded orange crystals of [Ti(2)(&mgr;(1,7)-OC(10)H(6)O)(2)(&mgr;(1,7):eta(2),eta(1)-OC(10)H(6)OH)(2)(O(i)Pr)(2)](infinity) (5). Diffraction studies were conducted at the Cornell High Energy Synchrotron Source (CHESS) because of the small crystal sizes. 2 (C(18)H(14)O(6)Ti, monoclinic, P2(1)/n, a = 9.624 (2), b = 11.283 (2), c = 14.916 (3), beta = 90.47(3) degrees, Z = 4), 4 (C(32)H(33)NO(14)Ti(2), monoclinic, P2(1)/n, a = 16.137 (3), b = 10.762 (2), c = 20.368 (4), beta = 111.65(3) degrees, Z = 4), and 5 (C(23)H(20)O(5)Ti, orthorhombic, Pbca, a = 11.095 (2), b = 17.970 (4), c = 19.484 (4), Z = 8) are 3-dimensional materials based on diaryloxide connectivity between geometrically similar edge shared (i.e., Ti(2)(&mgr;-OAr)(2)) bioctahedral dititanium building blocks. While 2 and 5 possess a roughly body-centered arrangement of dititanium units, 4 has a hexagonal secondary structural motif. The nature of crystallization through alcoholysis is also discussed.

Fluorescence Anisotropy Assays Reveal Affinities of C- and O-Glycosides for Concanavalin A(1)

The free energies of binding of various C- and O-glycosides to the lectin concanavalin A were measured using fluorescence anisotropy. Fluorescein derivatives of mannose and glucose were synthesized and were shown to bind to concanavalin A with free energies of -5.1 and -4.3 kcal mol(-)(1), respectively. Competition experiments were performed to determine the binding energies of different nonfluorescent carbohydrates, and the results were in excellent agreement with the binding energies determined by microcalorimetry. The minimum carbohydrate epitope that fills the lectin carbohydrate binding site, methyl 3,6-di-O-(alpha-mannopyranosyl)-alpha-mannopyranoside, competes directly for the site with the fluorescent ligands, indicating that the fluorescent ligands bind specifically. The binding affinities of C-glycosides to concanavalin A were compared with those of O-glycosides. The free energies of binding for corresponding C- and O-glycosides differed by less than 0.5 kcal mol(-)(1), indicating that recognition properties of C- and O-glycosides are very similar. It was found that for some ligands the use of a carbon linkage rather than an oxygen linkage caused the specificity of binding to decrease slightly.