Oxa-thia-, oxa-selena and crown ether macrocyclic complexes of tin(II) tetrafluoroborate and hexafluorophosphate - synthesis, properties and structures

The reactions of Sn(BF4)(2) and Sn(PF6)(2) with crown ethers and oxa-thia- or oxa-selena-macrocycles are complex, with examples of fragmentation of the fluoroanions, and cleavage of the ligands observed, in addition to adduct formation. The reaction of Sn(BF4)(2) with 15-crown-5 or 18-crown-6 produced the sandwich complex [Sn(15-crown-5)(2)][BF4](2) with 10-coordinate tin, and [Sn(18-crown-6)(H2O)][BF4](2)center dot 2H(2)O which has an hexagonal pyramidal tin centre with two long contacts to lattice water molecules (overall 7 + 2 coordination). [Sn(18-crown-6)(PF6)][PF6] is formed from 18-crown-6 and Sn(PF6)(2), but the hexafluorophosphate ions hydrolyse readily in these systems to produce F-which coordinates to the tin to produce [Sn(18-crown-6)F][PF6], which can also be made directly from Sn(PF6)(2), 18-crown-6 and KF in MeCN. The structure contains a hexagonal pyramidal coordinated Sn(II) cation with an apical fluoride. The oxa-thia macrocycle [18]aneO(4)S(2) forms [Sn([18]aneO(4)S(2))(H2O)(2)(PF6)][PF6], from which some crystals of composition [Sn([18]aneO(4)S(2))(H2O)(2)(PF6)(2)[PF6][F] were obtained. The cation contains an approximately planar O4S2 coordinated macrocycle, with two coordinated water molecules on one side of the plane and a weakly bound (kappa(2))PF6- group on the opposite face, and with the fluoride ion hydrogen bonded to the coordinated water molecules. In contrast, the oxa-selena macrocycle, [18]aneO(4)Se(2), produces an anhydrous complex [Sn([18]aneO(4)Se(2))(PF6)(2)] which probably contains coordinated anions, although it decomposes quite rapidly in solution, depositing elemental Se, and hence crystals for an X-ray study were not obtained. Reacting Sn(BF4)(2) and [18]aneO(4)Se(2) or [18]aneO(4)S(2) also causes rapid decomposition, but from the latter reaction crystals of the 1,2-ethanediol complex [Sn([18]aneO(4)S(2))-{C2H4(OH)(2)}][BF4](2) were isolated. The structure reveals the coordinated macrocycle and a chelating diol, with the O-H protons of the latter hydrogen bonded to the [BF4](-) anions. This is a very rare, structurally authenticated example of ring opening/cleavage of an oxa-thia macrocycle. The new complexes were characterised by microanalysis, IR, H-1, F-19{H-1} and P-31{H-1} NMR spectroscopy as appropriate, and X-ray structures are reported for [Sn(15-crown-5)(2)][BF4](3)[H3O]center dot H2O, [Sn(18-crown-6)(H2O)][BF4](2)center dot 2H(2)O, [Sn(18-crown- 6) F][PF6], [Sn([18]aneO(4)S(2))(H2O)(2)(PF6)](2)[PF6][F] and [Sn([18]aneO(4)S(2)){C2H4(OH)(2)}][BF4](2). The complexes are compared and contrasted with chloro-tin(II) complexes of crown ethers, germanium(II) and lead(II) analogues.