Aqua[5,17-di­hydroxy-11,23-di­methyl­bi­cyclo­[18.3.1.19,13]­hexacosa-1(25),2,7,9,11,13(26),21,23-octaene-25,26-diolato]­dinitrato-κ2O,O′;κO-gadolinium nitrate–methanol–water (1/0.5/1.75)