Most of the chemistry of antimony is characteristic of a nonmetal. Antimony has some definite cationic chemistry, SbO and Sb(OH) 2 being present in acidic aqueous solution; the compound Sb 8 (GaCl 4) 2, which contains the homopolycation, Sb 8, was prepared in 2004. It can form alloys with one or more metals such as aluminium, iron, nickel, copper, zinc, tin, lead, and bismuth. Antimony has fewer tendencies to anionic behaviour than ordinary nonmetals. Its solution chemistry is characterised by the formation of oxyanions. Like arsenic, antimony generally forms compounds in which it has an oxidation state of +3 or +5. The halides, and the oxides and their derivatives are illustrative examples. The +5 state is less stable than the +3, but relatively easier to attain than with arsenic. This is explained by the poor shielding afforded the arsenic nucleus by its 3d electrons. In comparison, the tendency of antimony (being a heavier atom) to oxidize more easily partially offsets the effect of its 4d shell. Tripositive antimony is amphoteric; pentapositive antimony is (predominately) acidic. Consistent with an increase in metallic character down group 15, antimony forms salts including an acetate Sb(CH 3 CO 2) 3, phosphate SbPO 4, sulfate Sb 2 (SO 4) 3 and perchlorate Sb(ClO 4) 3. The otherwise acidic pentoxide Sb 2 O 5 shows some basic (metallic) behaviour in that it can be dissolved in very acidic solutions, with the formation of the oxycation SbO 2. The oxide Sb 2 O 3 is polymeric, amphoteric, and a glass former. Antimony has an extensive organometallic chemistry (see Organoantimony chemistry).