Laboratory work is at the core of any chemistry curriculum but literature on the assessment of laboratory skills is scant. In this study we report the use of a peer-observation protocol underpinned by exemplar videos. Students are required to watch exemplar videos for three techniques (titrations, distillations, preparation of standard solutions) in advance of their practical session, and demonstrate the technique to their peer, while being reviewed. For two of the techniques (titrations and distillations), the demonstration was videoed on a mobile phone, which provide evidence that the student has successfully completed the technique. In order to develop digital literacy skills, students are required to upload their videos to a video sharing site for instructor review. The activity faciliated the issuing of digital badges to students who had successfully demonstrated competency. Students' rating of their knowledge, experience, and confidence of a range of aspects associated with each technique significantly increased as a result of the activity. This work, along with student responses to questions, video access, and observations from implementation are reported in order to demonstrate a novel and useful way to incorporate peer-assessment of laboratory skills into a laboratory programme, as well as the use of digital badges as a means of incorporating and documenting transferable skills on the basis of student generated evidence.

Waste electrical and electronic equipment (WEEE) such as mobile phones contain a plethora of metals of which gold is by far the most valuable. Here we describe a simple primary amide that achieves the selective separation of gold from a mixture of metals typically found in a mobile phone by extraction into toluene from an aqueous HCl solution; unlike current processes, reverse phase transfer is achieved simply using water. Phase transfer occurs by dynamic assembly of protonated and neutral amides with AuCl4 − anions through hydrogen bonding in the organic phase, as shown by EXAFS, mass spectrometry measurements and computational calculations, and supported by distribution coefficient analysis. We anticipate that the fundamental chemical understanding gained here is integral to the development of metal recovery processes, in particular through the use of dynamic assembly processes to build complexity from simplicity.

The recycling of metals from end-of-life secondary sources such as electronic waste remains a significant environmental and technological challenge currently detrimental to the development of circular economies. The complex nature of electronic waste, containing a myriad of different elemental metals, means that sophisticated yet simple separation methods need to be developed in order to recycle these valuable and often critical metal resources. In this work simple 2 primary, secondary, and tertiary amides are appraised as reagents that selectively transport gold from aqueous to organic phases in a solvent extraction experiment. While the strength of extraction of gold from single metal solutions is ordered 3 o >2 o >1 o , the 3 o and 2 o amides are ineffective at gold transport from mixed-metal solutions of concentrations representative of smartphones due to the formation of a third, dense phase. Increasing the polarity of the organic phase can negate third phase formation but at the expense of selectivity. The identities of the species that reside in the organic and third phases have been studied by a combination of slope analysis, mass spectrometry, NMR spectroscopy, and computational methods. These techniques show that protonation of the amide L occurs at the oxygen atom, resulting in the protonated dimer HL2 + which acts as a receptor for AuCl4 − to form dynamic supramolecular aggregates in the organic phase. The characterization of a tin complex in the third phase by X-ray crystallography supports these conclusions and furthermore, suggests the preference for the chelation of the proton by two amide molecules instead of the transport of hydronium into the organic phase and its subsequent use as structural template.

High anion selectivity for PtCl6(2-) over Cl(-) is shown by a series of amidoamines, R(1)R(2)NCOCH2CH2NR(3)R(4) (L1 with R(1) = R(4) = benzyl and R(2) = R(3) = phenyl and L3 with R(1) = H, R(2) = 2-ethylhexyl, R(3) = phenyl and R(4) = methyl), and amidoethers, R(1)R(2)NCOCH2CH2OR(3) (L5 with R(1) = H, R(2) = 2-ethylhexyl and R(3) = phenyl), which provide receptor sites which extract PtCl6(2-) preferentially over Cl(-) in extractions from 6 M HCl solutions. The amidoether receptor L5 was found to be a much weaker extractant for PtCl6(2-) than its amidoamine analogues. Density functional theory calculations indicate that this is due to the difficulty in protonating the amidoether to generate a cationic receptor, LH(+), rather than the latter showing weaker binding to PtCl6(2-). The most stable forms of the receptors, LH(+), contain a tautomer in which the added proton forms an intramolecular hydrogen bond to the amide oxygen atom to give a six-membered proton chelate. Dispersion-corrected DFT calculations appear to suggest a switch in ligand conformation for the amidoamine ligands to an open tautomer state in the complex, such that the cationic N-H or O-H groups are also readily available to form hydrogen bonds to the PtCl6(2-) ion, in addition to the array of polarized C-H bonds. The predicted difference in energies between the proton chelate and nonchelated tautomer states for L1 is small, however, and the former is found in the X-ray crystal structure of the assembly [(L1H)2PtCl6]. The DFT calculations and the X-ray structure indicate that all LH(+) receptors present an array of polarized C-H groups to the large, charge diffuse PtCl6(2-) anion resulting in high selectivity of extraction of PtCl6(2-) over the large excess of chloride.

An analysis of 552 structures of metal complexes of alkyl and arylphosphinates in the Cambridge Crystallographic Database shows that the phosphinate ligating group is remarkably versatile and is able to adopt ten different binding motifs in both mono-and polynuclear complexes in which an individual phosphinate group can bind to up to five metal atoms. The majority of both homo-and heteroleptic complexes contain M-O-PR2-O-M units in oligomeric and polymeric structures. In many heteroleptic complexes ligands containing hydrogen bond donors form strong bonding interactions with the phosphinate, generating pseudochelated structures. Similar pseudochelates, − O-PR2=O … H-O-PR2=O, are formed when both a phosphinate and its parent phosphinic acid are coordinated to a single metal atom. Such structures feature also in the solution chemistry involved in metal extraction processes using phosphinate ligands. As might be expected, many of the binding motifs found in phosphinate complexes are similar to those in carboxylate complexes but there are fewer examples of phosphinates being used to form metal organic frameworks.