[AI(OH)3]-

佢地本身就做complex ion 即係，佢地ion 入面form 左好多dative covalent bond ０既ion
因為AL 3+ 好缺電子，所以做左lewis acid (electron acceptor)(一 pair 過）而OH-０係外圍０個度有一完整對lone pair electron 多左出黎，自然就俾AL3+ attract ，form 左 dative covalent bond ---即係個對shared electron 全部由一個species (lewis base ) 俾的。

因為佢只係ion ，並不是compound
所以兩者也不是

as [AI(OH)4]-,[Cu(NH3)4]2+ are not neutral but charged, they are ions
[Al(OH)4]- is negatively charged and called anion
while [Cu(NH3)4]2+ is cation

in addition, these kinds of ions contain a central species Al3+, Cu2+ (neutral or charged), which is covalenty bonded with several ligands OH-, NH3 (neutral or charged), overall, they are called complex ion.

the formation and stability of these ion is result from
VACANT LOWER ORBITALS
to settle the
LONE PAIRS of the ligands

due to the highly positively charges on the central ion, great electrostatic attraction between ligands and it gather them.

electrostatic repulsion between the lone pairs and the outermost valence electrons triggers the rearrangement of the outermost electrons to spare more vacant orbitals at outermost subshell.

hybridization of outermost subshell and those at higher energy levels shapes the legands
for examples, d2sp3 hybrid allows the formation of octahedral complex, e.g. CrCl63-
sp3 hybrid allows the formaion of tetrahedral one, e.g. [AI(OH)4]-,[Cu(NH3)4]2+