Spectroscopic investigations on the structure and fluxionality of the trihaptocycloheptatrienyl complexes [MX(CO)2(LL)(η3-C7H7)] (M Mo, W; X I, Cl; LL bisphosphine or diamine) and synthesis of the tetracyanoethene adducts [WI(CO)2{Ph2P(CH2)nPPh2}{η3-C9H7(CN)4}] (n = 1 or 2)