Construction of coordination polymers of cadmium(II) with mixed hexamethylenetetramine and terephthalate or thiocyanate ligands

Hexamethylenetetramine: An old new building block for design of coordination polymers

Abstract: The design of new coordination polymers is nowadays a challenging research topic that attracts increasing interest due to the unique structural and functional properties of such metal-organic materials. In contrast to the recognized use of some N-donor ligands for the construction of coordination polymers, the application of hexamethylenetetramine (hmt) as a simple, commercially available, water-soluble and highly versatile cagelike building block has so far been explored to a lesser extent, although a considerable number of hmt-driven metal-organic networks have been reported in the last few years. Given the high potential of hmt for future developments of this research field, the present review summarizes the main structural and topological types of coordination polymers bearing hmt. These compounds feature a high diversity of topologies that include linear, zigzag, double, triple and quadruple 1D chains, rectangular grids, flat and undulating 2D layers, as well as layer-pillared, octahedral, zeolite-like, honeycomb-like and other complex 3D nets, in which hmt acts as a linker or spacer, pillar or connector, stabilizer and/or supporting ligand. The most common synthetic strategies are reviewed, showing that a diversity of metal-organic networks can be generated by facile self-assembly routes in aqueous medium and using rather simple chemicals. The main types of auxiliary ligands necessary for the construction of hmt-driven coordination networks are also identified. The additional structural features such as the formation of supramolecular networks and water clusters are described, and the selected properties and potential applications of hmt-containing coordination polymers as porous, magnetic or photoluminescent materials are highlighted.

Supramolecular architecture of cadmium(II)-terephthalate complexes having a tridentate or tetradentate Schiff base as blocking coligand

Abstract: Two new cadmium(II)–terephthalate complexes, ∞ 1 { [ Cd 2 ( μ - terephthalate ) 2 ( L 1 ) 2 ] · 9 H 2 O } (1) and [{Cd(H2O)(L2)}2(μ-terephthalate)](terephthalate) · 10H2O (2), where L1 = (E)-N1,N1-diethyl-N2-(1-(pyridin-2-yl)ethylidene)ethane-1,2-diamine; L2 = N,N′-bis-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine; terephthalate = benzene - 1 , 4 - dicarboxylate - O 2 C - C 6 H 4 - CO 2 - ) have been synthesized by a conventional solution method. Characterization by single crystal X-ray crystallography shows that compound 1 is composed of 1-D polymeric zig-zag chains with distorted pentagonal-bipyramidal cadmium centers. Compound 2 consists of centrosymmetric dinuclear complexes with a distorted pentagonal-bipyramidal cadmium center in which one terephthalate ligand bridges the metal centres and another terephthalate anion with water of crystallization forms a H-bonding network.

Synthesis, crystal structure, magnetic behavior and thermal property of three polynuclear complexes : [M(dca)2(H2O)2]n · (hmt)n [M = Mn(II), Co(II)] and [Co(dca)2(bpds)]n [dca, dicyanamide; hmt, hexamethylenetetramine; bpds, 4,4'-bipyridyl disulfide]

Abstract: Three μ1,5-dicyanamide bridged Mn(II) and Co(II) complexes having molecular formula [Mn(dca)2(H2O)2]n · (hmt)n (1), [Co(dca)2(H2O)2]n · (hmt)n (2) and [Co(dca)2(bpds)]n (3) [dca = dicyanamide; hmt = hexamethylenetetramine; bpds = 4,4′-bipyridyl disulfide] have been synthesized and characterized by single crystal X-ray diffraction study, low temperature (300–2 K) magnetic measurement and thermal behavior. The X-ray diffraction analysis of 1 and 2 reveals that they are isostructural, comprising of 1D coordination polymers [M(dca)2(H2O)2]n [M = Mn(II), Co(II) for 1 and 2, respectively] with uncoordinated hmt molecules located among the chains. The [M(dca)2(H2O)2]n chains and the lattice hmt molecules are connected through H-bonds resulting in a 3D supramolecular architecture. The octahedral N4O2 chromophore surrounding the metal ion forms via two trans located water oxygens and four nitrogens from four nitrile dca. Complex 3 is a 1D chain formed by two μ1,5-dca and one bridging bpds. The octahedral N6 coordination sphere surrounding the cobalt ions comprises four nitrogens from dca and two from bpds. Low temperature magnetic study indicates small antiferromagnetic coupling for all the complexes. Best fit parameters for 1: J = −0.17 cm−1, g = 2.03 with R = 6.1 × 10−4; for 2, J = −0.50 cm−1, and for 3, J = −0.95 cm−1.

Self-assembled molecular complexes and coordination polymers of CdII, hexamine, and monocarboxylates: structural analysis and theoretical studies of supramolecular interactions

Abstract: Four new cadmium(II) complexes [Cd2(bz)4(H2O)4(μ2-hmt)]·Hbz·H2O (1), [Cd3(bz)6(H2O)6(μ2-hmt)2]·6H2O (2), [Cd(pa)2(H2O)(μ2-hmt)]n (3), and {[Cd3(ac)6(H2O)3(μ3-hmt)2]·6H2O}n (4) with hexamine (hmt) and monocarboxylate ions, benzoate (bz), phenylacetate (pa), or acetate (ac) have been synthesized and characterized structurally. Structure determinations reveal that 1 is dinuclear, 2 is trinuclear, 3 is a one-dimensional (1D) infinite chain, and 4 is a two-dimensional (2D) polymer with fused hexagonal rings consisting of CdII and hmt. All the CdII atoms in the four complexes (except one CdII in 2) possess seven-coordinate pentagonal bipyramidal geometry with the various chelating bidentate carboxylate groups in equatorial sites. One of the CdII ions in 2, a complex that contains two monodentate carboxylates is in a distorted octahedral environment. The bridging mode of hmt is μ2- in complexes 1−3 but is μ3- in complex 4. In all complexes, there are significant numbers of H-bonds, C−H/π, and π−π interactions wh...

Synthesis, crystal structure and luminescent properties of one coordination polymer of cadmium(II) with mixed thiocyanate and hexamethylenetetramine ligands

Abstract: A novel Cd(II) coordination polymer [Cd(SCN)2(hmt)1/2(H2O)]2·H2O (hmt = hexamethylenetetramine) has been synthesized and characterized by IR, elemental analysis, TG technique and X-ray crystallography. Cd(II) atom has an distorted octahedral environment with an N3S2O donor set. Every six Cd(II) centers are linked by hmt and thiocyanato bridges to form a planar 2D coordination polymer containing hexagonal metallocyclic rings [Cd6(SCN)8(hmt)2]. A 2D layer structure is held together with its neighboring ones via a set of hydrogen-bonding interactions to form a 3D supramolecular structure. The luminescent properties of the title complex in the solid state were investigated.

Phase annealing in SHELX-90: direct methods for larger structures

Abstract: A number of extensions to the multisolution approach to the crystallographic phase problem are discussed in which the negative quartet relations play an important role. A phase annealing method, related to the simulated annealing approach in other optimization problems, is proposed and it is shown that it can result in an improvement of up to an order of magnitude in the chances of solving large structures at atomic resolution. The ideas presented here are incorporated in the program system SHELX-90; the philosophical and mathematical background to the direct-methods part (SHELXS) of this system is described.

An empirical method for correcting diffractometer data for absorption effects

Abstract: Absorption effects usually present the most serious source of systematic error in the determination of structure factors from single-crystal X-ray diffraction measurements if the crystal is not ground to a sphere or cylinder. A novel method is proposed for the correction of these effects for data collected on a diffractometer. The method works from the premise that the manifestation of systematic errors due to absorption, unlike most other sources of systematic error, will not be evenly distributed through reciprocal space, but will be localized. A Fourier series in the polar angles of the incident and diffracted beam paths is used to model an absorption surface for the difference between the observed and calculated structure factors. Knowledge of crystal dimensions or linear absorption coefficient is not required, and the method does not necessitate the measurement of azimuthal scans or any extra data beyond the unique set. Moreover, application of the correction is not dependent upon the Laue symmetry of the crystal or the geometry of the diffractometer. The method is compared with other commonly used corrections and results are presented which demonstrate its potential.

Evaluation of Single-Crystal X-ray Diffraction Data from a Position-Sensitive Detector

Abstract: A Fortran program has been developed for the reduction of single-crystal diffraction data from a sequence of adjacent rotation pictures recorded at a fixed X-ray wavelength by an electronic area detector. The electronic pictures (data frames) covering the first 5° of crystal rotation are used to locate strong diffraction spots and to estimate the background. The orientation of the crystal is derived automatically from the list of observed spots and all parameters describing the diffraction pattern are refined. The only input required from the user is the specification of the space group, approximate cell dimensions and detector setting. When the initialization step is finished the program goes back to the first picture and evaluates all data frames in the order they arrive from the measurement. Each element of an electronic picture (pixel) is labelled by the indices of the nearest reflection using the current refined parameters describing the diffraction geometry. If the pixels close to its nearest reflection the counts contribute to the three-dimensional profile; otherwise the counts are used to update the background. Each profile is represented as if the reflection had followed the shortest path through the Ewald sphere and had been recorded on the surface of the sphere. Reflections close to the Ewald sphere are kept in a hash table to allow rapid access for updating the profiles. Reflections which have completely passed through the Ewald sphere are removed from the table and saved for further processing. Intensities are estimated by fitting their profiles to an average shape learned from strong neighbouring reflections. Smoothly varying scaling factors are applied to the Lp-corrected intensities which minimize discrepancies between symmetry-related reflections and fit to a reference data set if available.

Construction of Porous Solids from Hydrogen-Bonded Metal Complexes of 1,3,5-Benzenetricarboxylic Acid

Abstract: The reaction of M(II) acetate hydrate (M = Co, Ni, and Zn) with 1,3,5-benzenetricarboxylic (BTC) acid yields a material formulated as M3(BTC)2·12H2O. These compounds are isostructural as revealed by their XRPD patterns and a single crystal structure analysis performed on the cobalt containing solid [monoclinic, space group C2, a = 17.482 (6) A, b = 12.963 (5) A, c = 6.559 (2) A, β = 112.04°, V = 1377.8 (8) A, Z = 4]. This solid is composed of zigzag chains of tetra-aqua cobalt(II) benzenetricarboxylate that are hydrogen-bonded to yield a tightly held 3-D network. Upon liberating 11 water ligands per formula unit a porous solid results, M3(BTC)2·H2O, which was found to reversibly and repeatedly bind water without destruction of the framework. The proposed 1-D channels of the monohydrate have a pore diameter of 4 × 5 A, which is typical of those observed in zeolites and molecular sieves. The successful inclusion of ammonia into the porous solid was demonstrated. Larger molecules and others without a reactiv...