Conformational Studies of Substituted Chromans: Crystal Structures of 2,2′-(1E,1′E)-(2,3-Dimethylchroman-2,4-diyl)bis(Azan-1-yl-1-ylidene)bis(Methan-1-yl-1-ylidene)Diphenol (I) and 2,2′-(1E,1′E)-(2-Ethyl-3-Methylchroman-2,4-diyl)bis(Azan-1-yl-1-ylidene)bis(Methan-1-yl-1-ylidene)Diphenol (II) |