Reactions of 2,4-hexadiyne-1,6-diol with [H2Os3(CO)9(PR3)] clusters. Cyclization of the diyne and reversible exchange of the phosphine ligands between different positions of the ?Os3C3? frameworkElectronic supplementary information (ESI) available: Tables S1?S36: Crystallographic data, atomic coordinates, bond lengths, bond angles, anisotropic displacement parameters, hydrogen coordinates and isotropic displacement parameters, and torsion angles for clusters IV, V, Va, VI, VIIa and VIII. See http://www.rsc.org/suppdata/dt/b4/b403861b/