Synthesis, detailed geometric analysis and bond-valence method evaluation of the strength of π-arene bonding of two isotypic cationic prehnitene tin(II) complexes: [{1,2,3,4-(CH3)4C6H2}2Sn2Cl2][MCl4]2 (M = Al and Ga)

. From solutions of prehnitene and the ternary halides (SnCl)[MCl4] (M = Al, Ga) in chlorobenzene, the new cationic SnIIâ€-arene complexes catena-poly- [chloridoaluminate(III)]-tri--chlorido-40 :1 2 Cl,1:2 4 Cl-[( 6 -1,2,3,4-tetramethylbenzene)tin(II)]-di--chlorido-2:3 4 Cl-[( 6 -1,2,3,4-tetramethylbenzene)- tin(II)]-di--chlorido-3:4 4 Cl-[chloridoaluminate(III)]--chlorido-4:10 2 Cl], [Al2Sn2Cl10(C10H14)2]n, (1) and catena-poly[chloridogallate(III)]-tri--chlorido-40 :1 2 Cl,1:2 4 Cl-[( 6 -1,2,3,4-tetramethylbenzene)tin(II)]-di--chlorido2:3 4 Cl-[( 6 -1,2,3,4-tetramethylbenzene)tin(II)]-di--chlorido-3:4 4 Cl-[chloridogallate(III)]--chlorido-4:10 2 Cl], [Ga2Sn2Cl10(C10H14)2]n, (2), were isolated. In these first main-group metalâ€prehnitene complexes, the distorted 6 arene - bonding to the tin atoms of the Sn2Cl2 2+ moieties in the centre of [{1,2,3,4- (CH3)4C6H2}2Sn2Cl2][MCl4]2 repeating units (site symmetry 1) is characterized by: (i) a significant ring slippage of ca 0.4 AËš indicated by the dispersion of Snâ€C distances [1: 2.881 (2)â€3.216 (2) AËš ; 2: 2.891 (3)â€3.214 (3) AËš ]; (ii) the non-methylsubstituted arene C atoms positioned closest to the SnII central atom; (iii) a pronounced tilt of the plane of the arene ligand against the plane of the central (Sn2Cl2) 2+ four-membered ring species [1: 15.59 (11), 2: 15.69 (9)]; (iv) metal†arene bonding of medium strength as illustrated by application of the bondvalence method in an indirect manner, defining the -arene bonding interaction of the SnII central atoms as s(SnIIâ€arene) = 2 s(SnIIâ€Cl), that gives s(SnIIâ€arene) = 0.37 and 0.38 valence units for the aluminate and the gallate, respectively, indicating that comparatively strong main-group metalâ€arene bonding is present and in line with the expectation that [AlCl4] is the slightly weaker coordinating anion as compared to [GaCl4] .