Thursday, August 13, 2009

What is a correct InChI for chromate?

During the IUPAC International Chemical Identifier (InChI) Subcommittee meeting in Glasgow last month, we touched upon the issue of normalisation of metal complexes. I did not realise before that even simple entity such as chromate(2−), drawn in different ways (a)(c), will give different InChIs. (And different standard InChIs as well; and InChIKeys too.) This is, I am told, because the current InChI algorithm involves “disconnection” of metals before “normalisation”, while it really should do normalisation first. Bother.

[Cr(O)2(O-)2]
(a)
InChI=1/Cr.4O/q;;;2*-1
[Cr(O)4]2-
(b)
InChI=1/Cr.4O/q-2;;;;
[Cr(2+)(O-)4]
(c)
InChI=1/Cr.4O/q+2;4*-1

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