cis-Protected palladium(ii) based binuclear complexes as tectons in crystal engineering and the imperative role of the cis-protecting agent

The shape and molecular packing of cis-protected Pd(ii) based binuclear complexes depends upon the ligand and cis-protecting agents.

Self-assembly of Cationic, Hetero- or Homo-nuclear Ru(II) Macrocyclic Rectangles and their Photophysical, Electrochemical and Biological Studies

A series of supramolecular rectangles, including two mixed-metal Ru/Pt complexes, have been formed by the coordination-driven self-assembly of a range of arene-Ru "molecular clip" acceptors (1a-1d) with rigid dipyridyl-based ligands (2a-2d) over the course of 10 hours in solution. The isolated products were characterized by multinuclear NMR ((1)H and (13)C or (31)P), HR-ESI-MS and an X-ray diffraction study to support the ascribed two-component rectangular structures. The rectangles were further characterized by UV-Vis and fluorescence studies. The redox behaviors of rectangles 3ca and 3da were also determined using cyclic voltammetry. Additionally, the antitumor activities of the suite of rectangles were determined against various human cancer cell lines and significant activity was shown by complexes 3ca, 3da, 3cb, 3cc and 3cd, with IC(50) values as low as 2.65 μM.

Ruthenium-oxygen coordination-driven self-assembly of a Ru(II)8 incomplete prism: synthesis, structure, and shape-selective molecular recognition study

Coordination-driven self-assembly of 1,3,5-benzenetricarboxylate (tma; 1) and oxalato-bridged p-cymeneruthenium(II) building block [Ru(2)(μ-η(4)-C(2)O(4))(MeOH)(2)(η(6)-p-cymene)(2)](O(3)SCF(3))(2) (2) affords an unusual octanuclear incomplete prism [Ru(8)(η(6)-p-cymene)(8)(tma)(2)(μ-η(4)-C(2)O(4))(2)(OMe)(4)](O(3)SCF(3))(2) (3), which exhibits a remarkable shape-selective binding affinity for neutral phenolic compounds via hydrogen-bonding interactions (p-cymene = p-(i)PrC(6)H(4)Me). Such a binding was confirmed by single-crystal X-ray diffraction analysis using 1,3,5-trihydroxybenzene as an analyte.

Self-assembled Pd(II) metallocycles using an ambidentate donor and the study of square-triangle equilibria

The self-assembly reaction of a cis-blocked 90 degrees square planar metal acceptor with a symmetrical linear flexible linker is expected to yield a [4 + 4] self-assembled square, a [3 + 3] assembled triangle, or a mixture of these. However, if the ligand is a nonsymmetrical ambidentate, it is expected to form a complex mixture comprising several linkage isomeric squares and triangles as a result of different connectivities of the ambidentate linker. We report instead that the reaction of a 90 degrees acceptor cis-(dppf)Pd(OTf)(2) [where dppf = 1,1'-bis(diphenylphosphino)ferrocene] with an equimolar amount of the ambidentate unsymmetrical ligand Na-isonicotinate unexpectedly yields a mixture of symmetrical triangles and squares in the solution. An analogous reaction using cis-(tmen)Pd(NO(3))(2) instead of cis-(dppf)Pd(OTf)(2) also produced a mixture of symmetrical triangles and squares in the solution. In both cases the square was isolated as the sole product in the solid state, which was characterized by a single crystal structure analysis. The equilibrium between the triangle and the square in the solution is governed by the enthalpic and entropic contributions. The former parameter favors the formation of the square due to less strain in the structure whereas the latter one favors the formation of triangles due to the formation of more triangles from the same number of starting linkers. The effects of temperature and concentration on the equilibria have been studied by NMR techniques. This represents the first report on the study of square-triangle equilibria obtained using a nonsymmetric ambidentate linker. Detail NMR spectroscopy along with the ESI-mass spectrometry unambiguously identified the components in the mixture while the X-ray structure analysis determined the solid-state structure.

Solvent-Induced Structural Changes in Complexes of 1,2-Bis(3-(3-pyridyl)pyrazolyl)ethane

A series of complexes have been obtained using the flexible ditopic ligand 1,2-bis(3-(3-pyridyl)pyrazolyl)ethane (LEt) with M(SCN)2 (M = Co, Fe) and ZnCl2. The ligand is observed to exist in a variety of conformations with rotations around the ethane spacer and around the pyridyl/pyrazole bond. The bridging length of the ligand (i.e., distance between pyridyl nitrogen atoms) varies by 3.5 Å depending on its geometry. Three different cobalt(ii) complexes of the general form [Co(LEt)2(SCN)2]·Solv (where Solv is a variable number/type of non-coordinated solvent) have been structurally characterized and form a series of solvent dependant supramolecular isomers. When Solv = 2MeCN a (4,4)-sheet is formed (1), however, when Solv = H2O an alternate ‘collapsed’ (4,4)-sheet is observed (2). Changing the solvent to two molecules of N,N-dimethylformamide (DMF) leads to a radical change in structure with a one-dimensional (1D) polymer formed (3) that contains two bridging ligands between adjacent metal atoms (i.e., maintaining the same metal/ligand ratio as in the (4,4)-sheet structures). A monomeric thiocyanate complex [Fe(LEt)2(SCN)2(H2O)2] (4) is reported in which the bispyridyl ligands are terminal and partake in an extended hydrogen-bonded network. A 1D polymer [Zn(LEt)Cl2] (5) is also presented. The structures of the metal complexes are contrasted with that of the free ligand.