Guest Ligand Research Articles

Ligand entrapment in twofold interpenetrating PtS matrixes by metallo-organic frameworks.

Single-crystal X-ray crystallography was used to determine the structures of four metallo-organic frameworks (MOFs). A dendritic tetradentate ligand (tetrakis(isonicotinoxymethyl)methane, TINM) was used with first-row transition-metal elements copper, nickel, and cobalt to synthesize MOFs with a PtS interpenetration, due to both planar and tetrahedral junctions being present in the framework. Two different polymeric complexes, 1 and 2, were obtained from similar starting materials, TINM and Cu(NO(3))(2).3H(2)O, but different solvents. The use of dichloromethane in addition to methanol and water promoted the coordination of nitrate ions to the copper. With only methanol and water used as solvent, the copper atom was coordinated to water molecules instead. Compound 1 has pores going through the structure in two dimensions, along crystallographic axes a and c with diameters of the pores (the diameters correspond to the minimum distances between van der Waals surfaces of opposing walls defined by projection along channel axis) approximately 1.0 x 3.1 and 2.5 x 3.7 A, respectively. Compound 2 has channels along all crystallographic axes. The dimensions of the channels are 3.2 x 3.7, 3.7 x 5.0, and 2.8 x 4.1 A, respectively. The structures of 3 and 4 entrap a large guest ligand molecule in the framework. The guest ligand is uncoordinated, although the pattern that the entrapped guests form brings the two arms of any two guests within close range. The lack of 3-fold penetration is due to only two arms being close to each other and also the fact that there is no space for an additional set of metal centers.

Hydrogen bonding and CH/π interactions for the stabilization of biomimetic zinc complexes: first examples of X-ray characterized alcohol and amide adducts to a tetrahedral dicationic Zn center

X-Ray analysis of two biomimetic (N3ZnL)2+ complexes with L = ethanol and formamide revealed that hydrogen bonding and CH/π interactions between the guest ligand L and the calix[6]arene host structure play a key role in their stabilization.

A platinum-linked porphyrin trimer and a complementary aluminium tris[3-(4-pyridyl)acetylacetonate] guest

A cyclic trimeric porphyrin host has been synthesised with alkyne–platinum–alkyne linkages; binding of the octahedral aluminium tris[3-(4-pyridyl)acetylacetonate] guest ligand into the complementary cavity of the host induces an asymmetry which is readily detected by NMR spectroscopy. The ligand complementarity unambiguously establishes the structure of this complex artificial receptor, but did not lead to an effective templated synthesis. A platinum-linked tetramer was also tentatively identified, but the absence of a suitably complementary ligand reduces the confidence that can be placed in this larger, and highly flexible, structure. These results demonstrate the strengths, and limitations, of metal coordination chemistry for assembling supramolecular architectures.

A platinum-linked cyclic porphyrin trimer

A cyclic trimeric porphyrin host is synthesised from monomer via alkyne–platinum–alkyne linkages; binding of the octahedral aluminum tris[3-(4-pyridyl)acetylacetonate] guest ligand into the complementary cavity of the host induces an asymmetry, which is readily detected by NMR spectroscopy.

Clathrates of tetracyanonickelates containing 1,4-dioxane

It was found after study of modifications of tetracyano complexes with 1,4-dioxane that a similar product is formed also by direct addition of 1,4-dioxane to a solution of [Ni(NH3)m][Ni(CN)4] or to solid NiNi(CN)4.nH2O; and 1,4-dioxane is initially bonded as a guest molecule and then as a ligand. The amount of guest component or ligand in the compounds Ni(NH3)m(C4H8O2)aNi(CN)4.(y-a)C4H8O2.nH2O and Ni(C4H8O2)aNi(CN)4.(n-a)C4H8O2 depends on the preparation conditions and on the conditions of storage of the solid product after isolation. The results of TA, IR, and GC analysis confirmed the presence of 1,4-dioxane bonded as a guest component and also 1,4-dioxane entering the host structure as a ligand.

Electrostatic Complementarities between Guest Ligands and Host Enzymes

A method is described for visualizing electrostatic complementarity between a guest ligand and a host enzyme by using molecular graphics and drawing a correlation map. First, two kinds of electrostatic potentials were calculated and illustrated on the surface of the guest molecule. One is due to the host enzyme and the other is due to the guest molecule itself. Second, the correlation between these two molecular surfaces was calculated and illustrated. Simultaneously, the correlation map was given with a well-defined correlation coefficient. This method provides a helpful tool for understanding the specific electrostatic recognition geometrically and quantitatively.