# Ionic or covalent in tetrahydroxoaluminate ion?

by Bipolarity
Tags: covalent, ionic
 P: 774 Consider the metal-ligand complex of the tetrahydroxoaluminate ion. $$[Al(OH)_{4}]^-$$ In this ion, the aluminium is bonded with four hydroxides where each hydroxide is a ligand. My question: Is the aluminium-hydroxide bond ionic or covalent? I can think of the ionic one working in someway like this: $$Al^{+3} + 4(OH)^- \rightarrow [Al(OH)_{4}]^-$$ I can also think of it as being covalent: $$Al + 3(OH) + (OH)^- \rightarrow [Al(OH)_{4}]^-$$ Which would be more "correct"? Aluminium is a metal, so you would expect it to form ionic bonds right? But I heard of instances where metals form covalent bonds, especially in metal complexes. So I hope I can clear this confusion in my head somehow. Also, will a complete octet be formed in both cases? Thanks! BiP
 P: 15 I would go for covalent bonding it seems more appropriate, Hydroxide ions do posses a lone pair of electrons. Hence they can provide both the electrons to form a dative covalent bond. Metal complexes do commonly form covalent bonds, especially transition metals. the metal complex will form a tetrahedral structure in this case hydroxide ions act as ligands... http://www.see.murdoch.edu.au/info/s...equations.html click on the link and look for equations 27-29

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