To our great satisfaction, three of the studied compounds (3, 7, 8) demonstrated strong interaction between nitro group and iodine (Fig. 2). This bond is included into a T-shaped hypervalent formation with I-C bond and a bond between iodine and a substituent at it.
o-Nitroiodobenzene dichloride 2 and diacetate 5 have no “vacancy” for formation of a T- shaped structure and therefore no bond between nitro group and iodine is formed.
The hypervalent iodine derivatives of o-nitroiodobenzene thus can be referred to two structural types: one – compounds 3, 7, 8 with covalent bond between O and I and a 5-ring geometry close to coplanar; another – compounds 2 and 5 with no or little covalent interaction between O and I and non-coplanar geometry, structurally similar to dinitroiodobenzene.
The strongest interaction between nitro group and iodine is in o-nitrophenylhydroxyiodonium trifluoroacetate 8. This compound, in our opinion deserves a special attention. Bond O-I of 2.51 Å is only slightly (~ 0.2 Å) longer than in iodoxole (2.30 Å)20. The 5-membered ring is nearly coplanar (the biggest dihedral angle N-C-C-I is 3.0o). C-C-N and C-C-I angles are close to 120o. Like in iodoxole, C-I-O angle is distorted from optimal 90o and is 71.2o. In a crystalline state protonated iodosyl group and trifluoroacetate anion form a hydrogen bond (distance O-H = 1.78 Å, .O-H-O = 170o).
This compound has structural features of three different classes of compounds and the question should be raised - what is the correct chemical name for it?
It’s a salt of o-nitroiodosylbenzene and trifluoroacetic acid, therefore we can call it o- nitrophenyliodosylium trifluoroacetate. The support for this name would be preparation of structurally similar salts from o-nitroiodosobenzene with other acids like trichloroacetic, other perfluorocarboxylic, toluenesulfonic, nitric, etc.
It’s a compound with two radicals and a positive charge at iodine atom, therefore we can call it hydroxy(o-nitrophenyl)iodonium trifluoroacetate. This name would be supported by conversion of this compound to salts with other anions without exchange of a proton of HO- group or by HO-transfer reactions, similar to aryl transfer in diaryliodonium salts. However, it seems impossible to distinguish between the two names. Formation of other salts would support both, and HO-transfer can be explained as well-known oxidation by iodosyl compounds.
Most interestingly, it’s a heterocyclic compound of a new type; therefore we can call it benziodoxazolium trifluoroacetate. To support this name, an exchange of substituents at 5-ring would be decisive factor – like substitution of HO to MeO or substitution of the second oxygen in a nitro group to another moiety, for instance PhN=.
Crystals of o-nitroiodylbenzene 3(benziodoxazol oxide?) are built of molecules of two types, both having nearly coplanar five-membered ring and intramolecular O-I distances of 2.77 Å and 2.68 Å, respectively (in benziodoxol oxide – 2.32 Å21 or 2.26 Å22). The shortest distance between these two molecules is 2.86 Å, however, other O-I intermolecular distances are also short, the shortest is 2.52 Å in a flat rhombic fragment formed by two iodyl groups of type (1). The O-I distance in 2-nitrodiphenyliodonium iodide 7 (phenylbenziodoxazolonium iodide?) is 2.74 Å, also just slightly longer than in carbon analog (2.48 Å).20 The difference between derivatives of o-nitroiodobenzene and corresponding isoelectronic derivatives of o-iodobenzoic
