Formation of 2,4,5-triaryl-4,5-dihydro-1H-imidazoles, (1), from aryl aldehydes. Crystal structures of cis-(1: aryl = pyridin-2-yl), {trans-[(1: aryl = pyridin-2-yl)H]+[OAc]−·3H2O}, {cis-[1: aryl = thien-2-yl]·0.5H2O} and trans-(1: aryl = thien-2-yl)