Crystal structure of bis­(μ2-4-tert-butyl-2-formyl­phenolato)-1:2κ3O1, O2:O1;3:4κ3O1, O2:O1-bis­(4-tert-butyl-2-formyl­phenolato)-2κ2O1, O2;4κ2O1, O2-di-μ3-methoxido-1:2:3κ3O;1:3:4κ3O-di-μ2-methoxido-1:4κ2O;2:3κ2O-tetra­copper(II). (March 2015)