Now showing 1 - 6 of 6
  • Publication
    A Bridge Too Far: Testing the Limits of Polypyridyl Ligands in Bridging Soluble Subunits of a Coordination Polymer
    Starting with a coordination polymer, {[Cu(L)]2}n (1 where H2L = salicylidene-2-aminophenol), we have explored the ability of polypyridyl ligands (P) to bridge the monomer complex to form nine {[Cu(L)]2(P)} complexes. The identity and solution stability of the [Cu(L)] units has been investigated through a novel combined UV-vis/EPR experiment and it has been found to be a stable supramolecular building unit for the construction of discrete complexes and coordination polymers. The reorganization of [Cu(L)] units to a new coordination polymer on addition of 4, 4′- bipyridine markedly changes the connectivity of the structure and the magnitude of the antiferromagnetic interactions through reorientation of the Cu(II) orbitals. We also present the structure of 1, 80 years after its synthesis was first reported.
      423Scopus© Citations 11
  • Publication
    A 13C-NMR study of azacryptand complexes
    An azacryptand has been solubilised in aqueous media containing 50% (v/v) dimethyl sulphoxide. 13C-NMR has been used to determine how the azacryptand is affected by zinc binding at pH 10. Using 13C-NMR and 13C-enriched bicarbonate we have been able to observe the formation of 4 different carbamate derivatives of the azacryptand at pH 10. The azacryptand was shown to solubilise zinc or cadmium at alkaline pHs. Two moles of zinc are bound per mole of azacryptand and this complex binds 1 mole of carbonate. By replacing the zinc with cadmium-113 we have shown that the 13C-NMR signal of the 13C-enriched carbon of the bound carbonate is split into two triplets at 2.2 °C. This shows that two cadmium complexes are formed and in each of these complexes the carbonate group is bound by two magnetically equivalent metal ions. It also demonstrates that these cadmium complexes are not in fast exchange. From temperature studies we show that in the zinc complexes both complexes are in fast exchange with each other but are in slow exchange with free bicarbonate. HOESY is used to determine the position of the carbonate carbon in the complex. The solution and crystal structures of the zinc–carbonate–azacryptand complexes are compared.
      621Scopus© Citations 4
  • Publication
    Organization of spin- and redox-labile metal centers into Langmuir and Langmuir-Blodgett films
    New sal2(trien) ligands that contain alkoxy substituents of various length in meta position of the salicyl entities were coordinated to electronically and magnetically active iron(III) and cobalt(III) centers. The electrochemical and spectroscopic properties of these amphiphilic complexes are virtually unaffected upon alteration of the alkoxy substituents, thus providing a system in which the physical behavior and the metal-centered chemical activity can be tailored independently. The amphiphilic character has been exploited for preparing Langmuir monolayers at the air-water interface and for constructing Langmuir-Blodgett films, hence allowing for hierarchical assembling of electronically and magnetically active systems. While Langmuir films were stable, transfer onto solid supports was limited, which restricted the magnetic analysis of the Langmuir-Blodgett assemblies.
      506Scopus© Citations 14
  • Publication
    Tethering of bi-nuclear complexes to SBA-15 and their application in CO2 hydrogenation
    Two bimetallic cryptates (containing Cu and Co), which have previously been shown to react with and activate atmospheric CO2, have been tethered to modified mesoporous SiO2 and their activities in promoting the CO2 + H2 reaction has been analysed. The cryptates have been tethered to –C3H6Cl modified SBA-15 through a condensation reaction between surface alkyl chlorides and 2° amines of the ligands releasing HCl and forming a 3° amine. The materials have been characterised using BET, TGA, FTIR and elemental analysis and their activity in promoting the CO2 + H2 reaction has been tested under batch reactor conditions. Co ions appear to selectively populate the medal sites of the tethered ligands while Cu ions appear to deposit on the surface as Cu(BF4)2 salts. The composite materials generate CO and CH4 from the CO2 + H2 mixtures. Co-containing catalysts are more effective than the Cu analogues in promoting the reaction.
      446Scopus© Citations 8
  • Publication
    Synthesis and self-assembly of spin-labile and redox-active manganese(III) complexes
    New amphiphilic and spin-labile Mn-III complexes based on dianionic N4O2-hexadentate sal(2)trien or sal(2)bapen ligands, which contain OC6H13, OC12H25, or OC18H37 alkoxy substituents at different positions of the salicylidene unit were prepared (H(2)sal(2)trien = N, N"'-bis(salicylidene)-1,4,7,10-tetraazadecane, H(2)sal(2)bapen = N, N"'-bis(salicylidene)-1,5,8,12-tetraazadodecane). According to electrochemical measurements, these complexes undergo two (quasi) reversible redox processes. Temperature-dependent magnetic measurements revealed a high-spin configuration for all sal(2)trien complexes (S = 2) and gradual spin crossover for sal(2)bapen complexes from high to low spin (S = 1). The chain length strongly influences the spin crossover, as C-18-functionalization stabilizes the low spin state at much higher temperatures than shorter alkyl chains. Moreover, long alkyl chains allow for spontaneous self-assembly of the molecules, which was investigated in single crystals and in Langmuir-films at the air-water interface. Long alkyl chains (C-12 or C-18) as well as a mutual syn-orientation of these molecular recognition sites were required for the Langmuir monolayers to be stable.
      692Scopus© Citations 41
  • Publication
    A magnetic iron(III) switch with controlled and adjustable thermal response for solution processing
    Spin crossover requires cooperative behaviour of the metal centers in order to become useful for devices. While cooperativity is barely predictable in solids, we show here that solution processing and the covalent introduction of molecular recognition sites allows the spin crossover of iron(III) sal2trien complexes to be rationally tuned. A simple correlation between the number of molecular recognition sites and the spin crossover temperature enabled the fabrication of materials that are magnetically bistable at room temperature. The predictable behaviour relies on combining function (spin switching) and structure (supramolecular assembly) through covalent interactions in a single molecular building block.
      461Scopus© Citations 36