Pyridine Complexes of Iodobismuthate(III) Anions

Round 1

Reviewer 1 Report

I found the work easy to read and well presented. The only part which could be strengthened is by adding a statement with pointers to the future on how this work may fit into the work of mataerial science advences. I know it can be difficul working with cyrstallographic data with the solvent and ligands positions causing problems which you have treated well. 

The work presented in this paper essentially reports the reactions of bismuth triiodide with readily available phosphonium salts, the key being the use of pyridine as a solvent which has a dramatic influence on the complex formation, both in terms of solvation and ligation. It has been many years since I last looked at reviews of bismuth chemistry, so I was surprised that these simple reactions had not been looked at in the interim. The actual synthesis is very simple adding the 2 reagents together in appropriate stoichiometries and crystalising the product(s). In this regard the simplicity makes the work elegant.  The closest literature work is that of Sharutin et al. in the late 2000’s.  There follows a study of the crystal structures of the product compounds. These are interesting structures in themselves with interesting iodide bridging features. I’m not a fan of listing selected bond lengths and angles in the text, given that its so easy to bring up a 3D molecular view, unless there is a very strong scientific point to make and so I found this the weakest point. However, others may differ on this point. One synthesis was carried out in different pyridine solution concentrations, and the resulting powers were examined by powder diffraction which showed the predominance of one molecular composition.  The structures themselves indicate how the pyridine influences the nature of the structures in comparison to the previously reported bipy complexes. It will be interesting to add quinoxalines and look for chain formation or aggregation. The second part of the work is the input of the crystallographic data into computational programs to examine charge distribution and molecular interactions. There is a section on Hirschfield analysis, and the generated surfaces are discussed. This if fine and the conclusions drawn seem reasonable. Overall, the paper was easy to read and had clearly been well proofed. There is the odd, unusual turn of phrase, but overall, it is written well and is a sound piece of work.  The S.I. is comprehensive with full cif check output data, well presented, tabulated crystallographic data and numerous output reports on Hirschfield anion interactions, together with surface visual data. Overall, I enjoyed reading this work which shows how simple synthesis without the need for inert atmospheres etc can be beautiful.

Reviewer 2 Report

The scientific content of the ms is interesting I thus favour the acceptance of this work in CRYSTALS. As a matter of fact, this is the best ms I have reviewed for this journal. I am sure that the paper will attract the interest of scientists working in the area of Bi(III), and especially in the chemistry and properties of halobismuthates(III). In particular, iodobismuthates(III) [reported in this work], are potential alternatives to iodoplumbates(II) in new photovoltaic devices, due to their narrow bandgap energies. Also, I believe that the article will receive a respectable number of citations in the future. Salient feautures of this work -which support my proposal for acceptance- are: (a) The complexes described have interesting molecular and supramolecular characteristics, belonging to four different structural types. (b) The complexes are rare examples of iodobismuthates(III) ligated with monodentate donors ; and (c) the bandgaps of the complexes are in the range 1.9- 2.2 eV and density- of- states KS- DFT calculations attribute the absorption to Bi(III)- centered charge transfer within the anionic unit. The ms is well written and nicely organized. The quality of figures is high and the references list covers the topic under study satisfactorily. The Supplementary Info is diagnostic and valuable, a model for authors.

Based on the above mentioned, I am more than happy to recommend acceptance of this fine piece of research in CRYSTALS. I do not have scientific points to raise: everything is well described and correctly explained. Thus I propose acceptance of the ms in its present form. Only a minor point, which can be corrected during the proof correction: the authors should use square brackets to indicate the coordination entities of the compounds, e.g., mer-[BiI₃Py₃].