Unusual neutral ligand coordination to arsenic and antimony trifluoride.

The preparations and spectroscopic characterisation of the hydrolytically unstable As(iii) complexes, [AsF3(OPR3)2] (R = Me or Ph) and [AsF3{Me2P(O)CH2P(O)Me2}] are described and represent the first examples of complexes of AsF3with neutral ligands. The crystal structure of [AsF3{Me2P(O)CH2P(O)Me2}] contains dimers with bridging diphosphine dioxide, but there are also long contacts between the dimers to neighbouring phosphine oxide groups, completing a very distorted six-coordination at arsenic and producing a weakly associated polymer structure. The reaction of AsF3with OAsPh3affords Ph3AsF2, and no arsine oxide complex was formed. Reaction of SbF3with OER3(R = Me or Ph, E = P or As), Me2P(O)CH2P(O)Me2and Ph2P(O)(CH2)nP(O)Ph2(n= 1 or 2) in MeOH produces [SbF3(OER3)2], [SbF3{Me2P(O)CH2P(O)Me2}] and [SbF3{Ph2P(O)(CH2)nP(O)Ph2}] respectively. The X-ray structures reveal that the complexes contain square pyramidal SbF3O2cores with apical F and cisdisposed pnictogen oxides. However, whilst [SbF3(OER3)2] (R = Ph: E = P or As; R = Me: E = As) and [SbF3{Ph2P(O)CH2P(O)Ph2}] are monomeric, [SbF3{Me2P(O)CH2P(O)Me2}] is a dimer with bridging diphosphine dioxides producing a twelve-membered ring, and [SbF3{Ph2P(O)(CH2)2P(O)Ph2}] is a chain polymer with diphosphine dioxide bridges. In the OAsR3reactions with SbF3, R3AsF2are also formed. Notably the Sb–O(P) bonds are shorter than As–O(P), despite the covalent radii (As < Sb), consistent with very weak coordination of the AsF3. IR and multinuclear (1H, 19F and 31P) NMR data are reported and discussed. BiF3does not react with pnictogen oxide ligands under similar conditions and halide exchange of bismuth chloro complexes with Me3SnF gave BiF3. [ABSTRACT FROM AUTHOR]