Av 2 400 spectrometer

All preparations were carried out under a dry dinitrogen atmosphere using standard Schlenk and glove box techniques. Anhydrous MgI 2 , CaI 2 , SrI 2 and BaI 2 were purchased from Sigma and used as received. Anhydrous [Sr(acac) 2 ] was prepared by dehydrating commercial [Sr(acac) 2 (H 2 O) 2 ] (Sigma): the hydrate was suspended in CH 2 Cl 2 over 4 Å molecular sieves and stirred gently for 2 weeks, then the suspension was decanted away and concentrated to dryness. [Ba(acac) 2 ] was synthesized by reacting BaI 2 and K(acac) in a 1 : 2 molar ratio in MeCN followed by extraction of KI with anhydrous acetone. Na[BAr F ] and [H(OEt 2 ) 2 ][BAr F ] were synthesized using Brookhart's procedure. 17 18-Crown-6 was purchased from Sigma and dried using SOCl 2 and the macrocycles [18]aneO 4 S 2 , [18]aneO 2 S 4 and [18]aneO 4 Se 2 were synthesized using literature procedures. 18 CH 2 Cl 2 and MeCN were dried by distillation from CaH 2 and n-hexane distilled from Na/K alloy. 1 H and 13 C{ 1 H} NMR spectra were recorded in CD 2 Cl 2 solution at 298 K using a Bruker AV II-400 spectrometer and are referenced to the residual CH 2 Cl 2 resonance. IR spectra were recorded as mulls between CsI plates using a Perkin-Elmer Spectrum 100 spectrometer over the range 4000-200 cm -1 . Microanalyses were undertaken at London Metropolitan University.

Infrared spectra were recorded as Nujol mulls or thin films between CsI plates using a Perkin Elmer Spectrum 100 over the range 4000-200 cm -1 and UV/visible spectra as powdered solids diluted with BaSO4, using the diffuse reflectance attachments of a Jasco V-670 or Perkin Elmer 750S spectrometer. Magnetic measurements were made on a Quantum Design MPMS XL7. 1 H NMR spectra were recorded from CD2Cl2 or CDCl3 solutions using a Bruker AV II 400 spectrometer and are referenced to the residual protio-solvent resonance. 31