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.

Dtphen and dmtphen are used to prepare four mononuclear Cd(II) complexes 1–4 to explore the substituent and anionic effects on the final cis/trans configuration of ligands and metal complexes. The slight difference of ligands results in the distinguishing alteration of dihedral angles between adjacent aromatic rings in ligands as well as the cis/trans conformation of metal complexes.Figure optionsDownload as PowerPoint slideHighlights
► A pair of Cd(II) nitrates of dtphen and dmtphen show cis and trans conformation in 1 and 2.
► Substituent effects of Me in dmtphen result in different dihedral angles of aromatic rings.
► Anionic effects of NO3−, Cl−, and Br− are studied in forming another two cis Cd(II) complexes.