let's take a look at IUPAC , shall we?
http://goldbook.iupac.org/C01203.htmlnow then, is Na
+(aq.) (quote)
A molecular entity formed by loose association involving two or more component molecular entities (ionic or uncharged) (...)
(unquote)
or is it not?
do we have (at least) two different sub-entities ?
yes , we do ( i.e. water, the sodium-ion )
are they at least "loosely associated" ?
yes, they are ( as we could learn from, for example, ion-mobility experiments: the what is moving
there is far bigger than the diameter usually assigned to the "naked" sodium ion), as the hull of water surrounding the ion is at least loosely bound to the ion itself, hence will have to move about with it.
following IUPAC's definition ( and this organization is the highest authority there is in chemistry), hydrated sodium is a complex.
(besides, it makes sense . but then again,"making sense " sometimes is irrelevant when you're talking definitions. so , better let's state: all elements required to fullfill the definition of a complex are being fullfilled by [Na(H
2O)
(approx. 6)]
+ , and therefore it IS a complex.
however, there might be some elder or individual definitions around still, like having to do with "empty d (or higher) metal orbitals, electron density of the ligand is donated to" and thatlike.
yeah, in this sense sodium ions, hydrated, are no complexes, simply as their empty d-orbitals are far far faaaaar away, and hence won't become occupied whilst solvation.
however , talking for me personally, I don't find those elder definitions very usefull for the problem at hand, i.e. explaining whats going on when sodium ions are being hydrated.
insofar, I agree with IUPAC
regards
Ingo