Fig. 4. Molecular structures of compounds 4 and 6 in the solid state. Ellipsoids are set at the 50% probability level; hydrogen atoms and co-crystallised solvent molecules are omitted for clarity and NHC ligands are depicted in wireframe for simplicity. Selected bond lengths (Å) and angles (°): 4: Al(1)–Al(2) 2.6035(13), Al(1)–C(1) 2.053(3), Al(1)–C(16) 2.079(3), Al(1)–C(53) 2.052(3), C(53)–C(54) 1.565(5), Al(2)–C(27) 2.048(3), Al(2)–C(42) 2.093(3), Al(2)–C(54) 2.040(3), Al(1)–Al(2)–C(54) 73.50(11), Al(2)–Al(1)–C(53) 72.94(11), C(54)–C(53)–Al(1) 101.33(19), C(53)–C(54)–Al(2) 101.23(19). 6: Al(1)–Al(1′) 2.5918(6), Al(1)–C(1) 2.0413(14), Al(1)–C(16) 2.1097(15), Al(1)–C(27) 2.0246(14), C(27)–C(27′) 1.3701(19), Al(1′)–Al(1)–C(27) 72.19(4), Al(1)–C(27)–C(27′) 107.09(10).