The Structure of ([W 3 Q 4 X 3 (dmpe) 3 ] + , Y - ) Ion Pairs (Q = S, Se; X = H, OH, Br; Y = BF 4 , PF 6 , dmpe = Me 2 PCH 2 CH 2 PMe 2 ) in Dichloromethane Solution and the Effect of Ion-Pairing on the Kinetics of Proton Transfer to the Hydride Cluster [W 3 S 4 H 3 (dmpe) 3 ] +