Richard Robson

Interpenetrating Nets: Ordered, Periodic Entanglement

Independent one-, two-, and even three-dimensional nets interpenetrate each other in many solid-state structures of polymeric, hydrogen-bonded nets and coordination polymers. For example, the interpenetration of the adamantane units of two diamondlike nets is shown on the right. A detailed and systematic examination of many interpenetrating nets of this kind is made, and implications for crystal engineering are discussed.

Einander durchdringende Netze: geordnete, periodische Verschlingung

Unaufloslich ineinander verwoben sind in vielen Festkorperstrukturen von polymeren, uber H-Brucken gebundenen Netzen und von Koordinationspolymeren die als voneinander unabhangig betrachteten ein-, zwei- oder gar dreidimensionalen Netzstrukturen. Rechts ist z. B. die gegenseitige Durchdringung der Adamantaneinheiten zweier diamantartiger Netze gezeigt. Aus der detaillierten Beschreibung und Systematik der mehrfachen gegenseitigen Durchdringung von derartigen Netzen in Festkorperstrukturen lassen sich unter anderem weitreichende Folgerungen fur das Kristall-Engineering ableiten.

A new type of interpenetration involving enmeshed independent square grid sheets. The structure of diaquabis-(4,4′-bipyridine)zinc hexafluorosilicate

Zn(4,4′-bipy)2SiF6·2H2O (4,4′-bipy = 4,4′-bipyridine) consists of two perpendicular and equivalent stacks of infinite, essentially square grid [Zn(H2O)2(4,4′-bipy)2]n2n+ sheets, which interpenetrate so that any particular sheet has an infinite number of perpendicular ones enmeshed or concatenated with it.

Ni(tpt)(NO3)2—A Three-Dimensional Network with the Exceptional (12,3) Topology: A Self-Entangled Single Net

The shortest circuits in the three-dimensional network with (12,3) topology of solvated Ni(tpt)(NO3 )2 pass through one another (see picture). This network based upon interlinked double helices occupies a unique position in the set of (n,3) nets. tpt=tri-4-pyridyl-1,3,5-triazine.

A Robust (10,3)‐a Network Containing Chiral Micropores in the AgI Coordination Polymer of a Bridging Ligand that Provides Three Bidentate Metal‐Binding Sites

Framework integrity is retained when water molecules replace the nitromethane molecules in the coordination polymer [Ag(hat)ClO4 ]⋅2 CH3 NO2 (see picture for structure), which are arranged in a helical fashion within the chiral micropores of the three-dimensional [Ag(hat)+ ]n network with a (10,3)-a topology. Remarkably, this is also the case after subsequent displacement of the water by nitromethane molecules. hat=1,4,5,8,9,12-hexaazatriphenylene.

A net-based approach to coordination polymers

True crystal engineering of coordination polymers with useful structure-based properties by design remains a distant prospect. The exploratory, experimental net-based approach to the construction of coordination polymers described in this article has provided a few examples of structures obtained by design, but also serendipitously revealed numbers of unprecedented and interesting structures that were totally unexpected. Further work with coordination polymers can confidently be expected to provide many similar surprises. It is proposed that carefully designed connecting ligands capable of binding metal centres strongly and predictably at chelating sites may afford improved structural control in network assembly and more robust network structures.

Structures of [Ag(tcm)], [Ag(tcm)(phz)1/2] and [Ag(tcm)(pyz)] (tcm=tricyanomethanide, C(CN)3-, phz=phenazine, pyz=pyrazine)

The topologically unique sheet structure of [Ag(tcm)] [tcm=the tricyanomethanide ion, C(CN)3-] is retained in the derivative [Ag(tcm)(phz)1/2] (phz=phenazine). The sheet structure is composite, consisting of two independent hexagonal grid nets which are corrugated so as to allow one to interpenetrate the other. The Ag+ ion is three-coordinate and provides half the three-connecting nodes of the hexagonal grid net, the others being provided by the tcm central carbon. [Ag(tcm)(phz)1/2] contains essentially the same composite double sheets linked together by phenazine units that bridge between silver centres which thereby become four-coordinate. The topology of [Ag(tcm)(pyz)] (pyz=pyrazine) is very different; in this case the Ag(tcm) component forms a planar, non-corrugated hexagonal grid and each such sheet is connected on both sides to neighbouring sheets by pyrazine bridging ligands whereby the silver becomes five-coordinate and trigonal bipyramidal. Two such 3,5-connected three-dimensional nets then interpenetrate.

A Simple Lithium(I) Salt with a Microporous Structure and Its Gas Sorption Properties

Much effort has been invested in studying the gas sorption properties of various classes of microporous materials such as zeolites, activated carbon materials, carbon nanotubes, polymers of intrinsic microporosity, and coordination polymers. At a time in the early 1990s when few coordination polymers had been deliberately constructed and characterized, their ability to sorb gases was a reasonable expectation. The first experimental measurements that heralded great promise of coordination polymers as materials for useful gas storage were reported by Kitagawa and co-workers in 1997. Subsequently, gas sorption by coordination polymers (more recently rebranded metal–organic frameworks (MOFs) by some) has become an intensively studied area. Low density is a most desirable characteristic of any gas storage material intended for mobile applications, and materials based on “light” metals (such as Li, Mg, and Al) are obvious targets for exploration. We report herein the synthesis, structure(s), and sorption properties of a simple salt of Li, lithium isonicotinate, which has a microporous structure and shows reversible gas uptake and release. Well-formed crystals of composition [(Li)(C6H4NO2 )]·0.5DMF (where C6H4NO2 is the isonicotinate anion, 1) can be readily obtained from DMF solution. The structure, which was determined by single-crystal X-ray diffraction, consists of a 3D [(Li)(C6H4NO2 )] network that contains microchannels occupied by DMF molecules. All the isonicotinate units are equivalent, and are associated with four Li centers, which are also all equivalent, and each associates with four isonicotinate anions. The structure can be readily envisaged in terms of [(Li)(C6H4NO2 )] chains (see Figure 1a), that are linked together by Li–N interactions into 2D sheets (see Figure 1b). The sheets in turn are linked together by Li–N interactions to form the 3D network (see Figure 1c). As can be seen in Figure 1a, each chain consists of alternating fourmembered rings (LiOLiO) and eight-membered rings (LiOCOLiOCO). The N centers of half of the pyridine units that

A wellsian ‘three-dimensional’ racemate: eight interpenetrating, enantiomorphic (10,3)-a nets, four right- and four left-handed

The crystal structure of solvated [Zn(tpt)2/3(SiF6)(H2O)2(MeOH)][tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine] is comprised of eight independent [Zn3(tpt)2]n networks with the (10,3)-a topology, four of one handedness and four of the other, which interpenetrate in a remarkable way, aspects of which were postulated by A. F. Wells almost twenty years ago.

Complexes of binucleating ligands. VIII. The preparation, structure and properties of some mixed valence cobalt(II)—cobalt(III) complexes of a macrocyclic binucleating ligand

Abstract The complex LCo2Br2·CH3OH has been isolated, where LH2 represents the macrocyclic tetrakis-Schiff base obtained by condensation of two molecules each of 1,3-diaminopropane and 2-hydroxy-5-methylisophthalaldehyde and L represents the derived dianion which behaves as a macrocyclic binucleating ligand. By oxidation of LCo2Br2·CH3OH with bromine under a variety of conditions the following products were isolated: LCo2Br3·H2O, two isomeric forms of LCo2Br3·2H2O, LCo2Br4·CH3OH, LCo2Br5·2CH3 OH, LCo2Br8·4CH3OH, (LH)CoBr6·2H2O and (LH4) Br6. Crystals of LCo2Br5·2CH3OH have been shown by X-ray diffraction methods to consist of binuclear [LCo(II)Co(III)Br2(CH3OH)2]+ cations, in which both metal centres are essentially octahedral, and tribromide anions. LCo2Br3·H2O, the two isomeric forms of LCo2Br3·2H2O and LCo2Br4·CH3OH are assigned the binuclear Co(II)Co(III) formulations, [LCo(II)Co(III)Br2(H2O)+Br−, [LCo(II)Co(III) Br2(H2O)2]+Br− in two geometrically isomeric forms and {[LCo(II)Co(III)Br2(CH3OH)]+}2Br−(Br3−) respectively, in which the cobalt(III) centres are six coordinate and low spin and the cobalt(II) centres are high spin and either five or six coordinate. LCo2Br8·4CH3OH is diamagnetic with a binuclear Co(III)Co(III) structure and is unstable in the solid, liberating bromine and regenerating the paramagnetic Co(II)Co(III) binuclear unit. (LH4)Br6 formulated as (LH42+) (Br3−)2, is the first example of a metal-free derivative of the macrocycle and can now be isolated from a metal-free condensation reaction of the dialdehyde and diamine components. Crystals of LCo2Br5·2CH3OH are orthorhombic with cell dimensions a = 17.78, b = 37.74 and c = 19.79 A, space group Pbca and Z = 16. Counter methods were used to collect 1993 reflections above background. Despite rapid decomposition of the crystal during data collection, the structural framework was ascertained readily and the structure refined to the limit of accuracy allowed by the quality of the data, using a least-squares method with isotropic temperature factors, to the somewhat high value of R 0.15.