Variation of cis/trans configuration of 3,8-dithiophen and 3,8-di-3-methylthiophen-substituted 1,10-phenanthroline in their cadmium(II) nitrate complexes originating from substituent and anionic effects

A pair of 3,8-dithiophen (dtphen) and 3,8-di-3-methylthiophen (dmtphen) substituted 1,10-phenanthroline cadmium(II) nitrates, formulated as [Cd(dmtphen)2(NO3)2] (1) and [Cd(dtphen)2(NO3)2] (2), exhibit cis and trans configuration in the whole complexes because of the substituent effects of methyl group in the dmtphen ligand. In 1 and 2, both ligands possess similar cis/trans configuration but different dihedral angles from 19.0(1)° to 45.5(1)° in 1 and 2.6(1)° to 5.9(1)° in 2 due to the spatial crowding effects of methyl group. Additionally, anionic effects of NO3−, Cl−, and Br− have been studied where two cis Cd(II) complexes formulated as [CdBr2(dmtphen)2] (3) and [CdCl2(dtphen)] (4) are obtained and the side thiophene and methyl-thiophene rings in each ligand adopt the cis/trans and trans/trans configuration relative to the central phen unit.