A ¹³C-NMR study of azacryptand complexes

Abstract

An azacryptand has been solubilised in aqueous media containing 50% (v/v) dimethyl sulphoxide. (13)C-NMR has been used to determine how the azacryptand is affected by zinc binding at pH 10. Using (13)C-NMR and (13)C-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 (13)C-NMR signal of the (13)C-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.

Bimetallic nickel complexes for selective CO2 carbon capture and sequestration

“…Additionally, Lu as well as Malthouse and coworkers showed evidence for a direct atmospheric CO 2 uptake by dinuclear copper 25 and zinc cryptands. 26 The uptake capability of these bimetallic cryptands and of dinuclear metalloenzymes as well as the high stability of the obtained carbonate complexes within those frameworks pointed our interest towards the application of dinickel azacryptands as highly selective CO 2 Reaction of the azacryptands 1 or 2 with Ni(ClO 4 ) 2 comprising the non-coordinative perchlorate anion afforded complexes 3 and 4 under inert atmosphere as crystalline material in 56% and 52% yield, respectively (Scheme 2). The composition of both complexes was unequivocally confirmed by structure analysis (Fig.…”

Hexanuclear Lanthanide Clusters Encapsulating a µ6-CO32−Ion Displaying an Unusual Binding Mode

“…The hexanuclear cluster can be visualized to be built up of two triangular units La1, La2 and La1* bridged by one of the carbonate oxygen O8 and the other two oxygens O8*, O8** of the carbonate bridges another triangular unit La2**, La1** and La2*. Further oxo groups of diketone connects these two trinuclear units leading to the formation of a novel hexanuclear cluster which is structurally different from hexanuclear clusters reported so far in literature . Carbonate anion is trapped in the center of the cluster core, interestingly here the carbonate anion adapts a new bridging mode µ 6 ‐η 1 :η 2 :η 1 :η 2 :η 1 :η 2 as shown in Figure b, assignment of bridging carbonate was further confirmed by careful observation of X‐ray diffraction data since carbonate source was not used in any stage of reaction.…”

Modulation of the CO2 fixation in dinickel azacryptands

“…Mass spectra were measured with a Shimadzu QP-2010 instrument. The dialdehydes 17,[34][35][36][37] as well as the azacryptands 20 and L I OH,Me 31 were synthesized according to literature procedures. All other chemicals were used as received from commercial vendors.…”

“…14 The stability and selectivity of the resulting compounds for the fixation of small molecules depend on the cage size as well as on the effective size of the small molecules. 9,10,13,[15][16][17][18] As a result, the uptake and binding properties of small molecules (e.g. halogenides and pseudohalogenides) can be selectively tuned by increasing the size of the cryptand and/or altering the binding motifs.…”