Construction of Low-Dimensional Cadmium Compounds with N2O/N2S Donor Tridentate Schiff Base Ligands

Abstract

Self-assemblies of two unsymmetrical tridentate N2O/N2S donor Schiff base ligands, that is, 2-((2-(dimethylamino)ethylimino)methyl)phenol (HL1) and methyl-2-pyridylmethylidenehy-drazinecarbodithioate (HL2), with different cadmium salts have led to 11 anion-controlled complexes, namely, [Cd(Ln)2] [n = 1 for 1 and n = 2 for 2], [Cd(L1)(HL1)](ClO4) (3), [Cd(HL2)(L2)](ClO4)(H2O) (4), [Cd(L2)Cl2] (5), [Cd(L1)Cl]2 (6), [Cd(L1)(NO3)]2 (7), [Cd(L2)(NO3)(CH3OH)]2 (8), [Cd(L2)(NO3)(H2O)]2 (8a), [Cd2(L1)2(SCN)2]n (9), and [CdL2(SCN)2]n (10), respectively. Eleven compounds were characterized by elemental analyses, IR spectra, MS and thermogravimetric analyses, of which 10 structures 2, 3, 4, 5, 6, 7, 8, 8a, 9, and 10 were further determined by single-crystal X-ray diffraction analyses. The compounds 2, 3, and 4 are mononuclear, in which the neutral molecule unit CdII(L2)2 (in 2) as well as cation units [CdII(HL1−2)(L1−2)]+ (L1 for 3 and L2 for 4) are respectively connected by hydrogen bonds C−H···S, O−H···O, and C−H···O and form three-dimensional (3D) ordered network structures. With the replacement of Cd(CH3COO)2/Cd(ClO4)2 by CdCl2/Cd(NO3)2 in the above reactions, because of the coordination interactions of nitrate and chloride anions in these cases, the obtained corresponding compounds 6−8 present dinuclear structures with planar Cd2O2/Cd2S2 quadrilateral cores and only compound 5 mononuclear, in which the folding effect of sulfur and solvent effect, to a certain extent, affect the microstructure of these complexes, such as the arrangements of the ligand L1−2 and nitrate/chloride ions. Furthermore, through intermolecular weak interactions, for example, C−H···O, O−H···N hydrogen bonding and π···π stacking, 3D supramolecular structures are assembled in these compounds. However, reactions of Cd(CH3COO)2/Cd(ClO4)2 + KSCN with L (L = L1(9), L2(10)) yield two one-dimensional (1D) chain-like compounds, and similarly, via interchain hydrogen bonds C−H···S (for 9) and N−H···N (for 10), 2D layer-like supramolecular networks are constructed. In addition, the photoluminescent properties of two ligands as well as 11 compounds were also studied.