Gravar-mail: Crystal structures and Hirshfeld surface analyses of 4,4′-{[1,3-phenyl­enebis(methyl­ene)]bis­(­oxy)}bis­(3-meth­oxy­benzaldehyde) and 4,4′-{[(1,4-phenyl­ene­bis(methyl­ene)]bis­(­oxy)}bis­(3-meth­oxy­benzalde­hyde)