Tin(ii) amide/alkoxide coordination compounds for production of Sn-based nanowires for lithium ion battery anode materials

Abstract

A series of tin(II) amide alkoxides ([(OR)Sn(NMe₂)]_n) and tin(II) alkoxides ([Sn(OR)₂]_n) were investigated as precursors for the production of tin oxide (SnO_x) nanowires. The precursors were synthesized from the metathesis of tin dimethylamide ([Sn(NMe₂)₂]₂) and a series of aryl alcohols {H-OAr = H-OC₆H₄(R)-2: R = CH₃ (H-oMP), CH(CH₃)₂ (H-oPP), C(CH₃)₃ (H-oBP)] or [H-OC₆H₃(R)₂-2,6: R = CH₃ (H-DMP), CH(CH₃)₂ (H-DIP), C(CH₃)₃ (H-DBP)]}. The 1 : 1 products were all identified as the dinuclear species [(OAr)Sn(μ-NMe₂)]₂ where OAr = oMP (1), oPP (2), oBP (3), DMP (4), DIP (5), DBP (6). The 1 : 2 products were identified as either a polymer ([Sn(μ-OAr)₂]_∞ (where OAr = oMP (7), oPP (8)), dinuclear [(OAr)Sn(μ-OAr)]₂ (where OAr = oBP (9), DMP (10) or DIP/HNMe₂ (11)), or mononuclear [Sn(DBP)₂] (12) complexes. These novel families of compounds (heteroleptic 1–6, and homoleptic 7–12) were evaluated for the production of SnO_x nanowires using solution precipitation (SPPT; oleylamine/octadecene solvent system) or electrospinning (ES; THF solvent) processing conditions. The SPPT route that employed the heteroleptic precursors yielded mixed phases of Sn^o : romarchite [1 (100 : 0); 2 (80 : 20); 3 (68 : 32); 4 (86 : 14); 5 (66 : 35); 6 (88 : 12)], with a variety of spherical sized particles [1 (350–900 nm); 2 (150–1200 nm); 3 (250–950 nm); 4 (20–180 nm); 5 (80–400 nm); 6 (40–200 nm)]. For the homoleptic precursors, similar phased [7 (80 : 20); 8 (23 : 77); 9 (15 : 85); 10 (34 : 66); 11 (77 : 23); 12 (77 : 23)] spherical nanodots were isolated [7 (50–300 nm); 8: (irregular); 10 (200–800 nm); 11 (50–150 nm); 12 (50–450 nm)], except for 9 which formed polycrystalline rods [Sn^o : romarchite (15 : 85)] with aspect ratios >100. From ES routes, the heteroleptic species were found to form ‘tadpole-shaped’ materials whereas the homoleptic species formed electrosprayed nanodots. The one exception noted was for 7, where, without use of a polymer matrix, nanowires of Sn^o, decorated with micron sized ‘balls’ were observed. Due to the small amount of material generated, PXRD patterns were inconclusive to the identity of the generated material; however, cyclic voltammetry on select samples was used to tentatively identify the final Sn^o (from 7) with the other sample identified as SnO_x (from 1).