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-(CH(3))(4)C(6)H(2)}(2)Sn(2)Cl(2)][MCl(4)](2) (M = Al and Ga)

From solutions of prehnitene and the ternary halides (SnCl)[MCl(4)] (M = Al, Ga) in chloro­benzene, the new cationic Sn(II)–π-arene complexes catena-poly[[chlorido­aluminate(III)]-tri-μ-chlorido-4′:1κ(2) Cl,1:2κ(4) Cl-[(η(6)-1,2,3,4-tetra­meth­yl­benzene)­tin(II)]-di-μ-chlorido-2:3κ(4) Cl-[(η(6)-1,2,3,4-tetra­methyl­benzene)­tin(II)]-di-μ-chlorido-3:4κ(4) Cl-[chlorido­aluminate(III)]-μ-chlorido-4:1′κ(2) Cl], [Al(2)Sn(2)Cl(10)(C(10)H(14))(2)](n), (1) and catena-poly[[chlorido­gallate(III)]-tri-μ-chlor­ido-4′:1κ(2) Cl,1:2κ(4) Cl-[(η(6)-1,2,3,4-tetra­methyl­benzene)­tin(II)]-di-μ-chlorido-2:3κ(4) Cl-[(η(6)-1,2,3,4-tetra­methyl­benzene)­tin(II)]-di-μ-chlorido-3:4κ(4) Cl-[chlor­ido­gallate(III)]-μ-chlorido-4:1′κ(2) Cl], [Ga(2)Sn(2)Cl(10)(C(10)H(14))(2)](n), (2), were isolated. In these first main-group metal–prehnitene complexes, the distorted η(6) arene π-bonding to the tin atoms of the Sn(2)Cl(2) (2+) moieties in the centre of [{1,2,3,4-(CH(3))(4)C(6)H(2)}(2)Sn(2)Cl(2)][MCl(4)](2) repeating units (site symmetry [Image: see text]) is characterized by: (i) a significant ring slippage of ca 0.4 Å indicated by the dispersion of Sn—C distances [1: 2.881 (2)–3.216 (2) Å; 2: 2.891 (3)–3.214 (3) Å]; (ii) the non-methyl-substituted arene C atoms positioned closest to the Sn(II) central atom; (iii) a pronounced tilt of the plane of the arene ligand against the plane of the central (Sn(2)Cl(2))(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 bond-valence method in an indirect manner, defining the π-arene bonding inter­action of the Sn(II) central atoms as s(Sn(II)—arene) = 2 − Σs(Sn(II)—Cl), that gives s(Sn(II)—arene) = 0.37 and 0.38 valence units for the aluminate and the gallate, respectively, indicating that comparatively strong main-group metal–arene bonding is present and in line with the expectation that [AlCl(4)](−) is the slightly weaker coordinating anion as compared to [GaCl(4)](−).