Gravar-mail: Bis[μ-2-(4-hy­droxy­phen­yl)acetato]-κ(3) O,O′:O;κ(3) O:O,O′-bis­{aqua­(4,4′-bipyridine-κN)[2-(4-hy­droxy­phen­yl)acetato-κ(2) O,O′]samarium(III)} monohydrate