Secondary bonding. Part 5. The crystal and molecular structures of phenyliodine(III) diacetate and bis(dichloroacetate)

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Abstract
The crystal structures of the title compounds (1) and (2) respectively have been determined at –60 °C from diffractometer data by the heavy-atom method. Crystals of (1) are orthorhombic, space group Pnn2, with unit-cell dimensions a= 15.693(3), b= 8.477(2), c= 8.762(2)Å, Z= 4, and R= 0.021 for 1 063 observed reflections. Crystals of (2) are triclinic, space group P with a= 10.462(3), b= 4.870(2), c= 15.445(5)Å, α= 101.03(3), β= 99.89(3), γ= 94.40(3)°, Z= 2, and R= 0.058 for 1 580 observed reflections. For (1) the results are in good agreement with a recent independent determination. In both (1) and (2) the iodine(III) atoms form three covalent bonds with distorted T-shaped geometry. The I–C distances in both compounds are the same (2.08–2.09 Å). The two I–O distances are the same (av. 2.156 Å) for (1) but differ significantly for (2)[2.136(6) and 2.163(7)Å]. The overall geometry of each iodine, however, can be described as a pentagonal-planar arrangement of three strong and two weak secondary bonds. In (1) both of these secondary I–O bonds are intramolecular. In (2), however, one of the ligands is unidentate, the other unsymmetrically bidentate, forming inter- and intra-molecular I ⋯ O contacts to give a dimeric arrangement. The formation and nature of the secondary bonds in (1) and (2) is discussed and compared with other pentagonal-planar systems. A possible orbital-overlap scheme is proposed to explain this geometry.

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