6,6′-Di-(8″-quinoline)-2,2′-bipyridine Cobalt(II) Complex

Round 1

Reviewer 1 Report

The work describes the synthesis and characterization of tetradentate ligand inspired by quaterpyridines which contains quinoline moieties. The ligand itself was never reported in the open literature but only in a Patent from the same authors and it deserves to be described in a publication. The work is well written, the synthesis and characterization of the compounds are well described.

The only comment that I have, concerns the sentence “3d metal ions show a tendency to bind qtpy in a tridentate fashion” (line 28). From this statement and the subsequent explanation, it seems that most of the time quaterpyridine binds to 3d metals as tridentate, but reading the paper (line 70- 71) and from the literature it is not so (see for example 10.1021/ja509077a Ni(0), 10.1039/DT9960002423 Ni(II), 10.1002/zaac.19824910117 Cu(II) and Co(II)). The bonding length of the “terminal” pyridine with the metal center are longer and the coordination of the whole ligand is weaker, however, clearly, in several cases tetradentate binding mode was obtained also with tetrapyridine and 3d metals. I think is better to revise lines from 28 to 31 to be clearer to the reader about what is previously reported in the literature. This does not mean that the positive quality of the new ligand facilitating the coordination should not be underlined.

Author Response

The authors agree with the points in the reviewer's comments. There are several factors that influence the coordination manner between the quaterpyridine and metal centers, including the metal ion size, the flexibility of quaterpyridine, and of course reaction conditions of coordination processes. We rewrote the second paragraph in the revised manuscript (changes with tracks), trying to introduce the background information in a more proper way.