residual electron density, 2.19/À2.18 e ä À3 .Compound 1 has crystallographic C i ( 1 1) site symmetry such that the asymmetric part of the crystal structure consists of 1/2 of a neutral cluster and one solvated acetone molecule; b) 2¥2 Me 2 CO: monoclinic; P2 1 / n; a ¼ 17.517(1), b ¼ 24.471(2), c ¼ 24.216(2) ä, b ¼ 106.233(1)8, V ¼ 9966.5(13) ä 3 ; Z ¼ 2, 1 calcd ¼ 2.878 Mg m À3 . Mo Ka data collected at 173(2) K with SMART CCD 1000 area detector diffractometer by 0.3w scans over 2q range 2.9±56.68; empirical absorption correction (SADABS) applied (m(Mo Ka ) ¼ 4.900 mm À1 ; max./min. transmission, 0.758/0.374). Anisotropic refinement (1044 parameters; 74 restraints) on 24 577 independent reflections converged at wR 2 (F 2 ) ¼ 0.158 with R 1 (F) ¼ 0.052 for I > 2s(I); GOF (on F 2 ) ¼ 0.99; max./min. residual electron density, 2.13/À2.56 e ä À3 . Compound 2 has crystallographic C i ( 1 1) site symmetry such that the asymmetric part of the crystal structure consists of 1/2 of a neutral molecule and one solvated acetone molecule. CCDC-195160 (1) and -195161 (2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/ retrieving.html (or from the Cambridge Crystallographic Data Centre,