Metal(II) Complexes Derived from Conformation Flexible Cyclic Imide Tethered Carboxylic Acids: Syntheses, Supramolecular Structures, and Molecular Properties

A series of mononuclear M­(II) complexes, namely, [Mn­(L1)2(H2O)4] (1), [Cu­(L1)2(pyr)2(H2O)2] (2),
[Zn­(L1)2(pyr)2(H2O)2]
(3), [Cd­(L1)2(pyr)2(H2O)2] (4), [Co­(L2)2(pyr)2(H2O)2].pyr (5), [Cu­(L2)2(pyr)2].2pyr.2H2O (6), and [Cd­(L2)2(pyr)2(H2O)2].pyr (7) (where L1H = 4-(1,3-dioxo-1,3-dihydro-isoindol-2-ylmethyl)-cyclohexanecarboxylic
acid, L2H = 4-(1,3-dioxo-1H,3H-benzo­[de]­isoquinolin-2-ylmethyl)-cyclohexanecarboxylic
acid, and pyr = pyridine) were synthesized and structurally characterized
by elemental analyses, IR spectroscopy, thermogravimetric analyses,
powder X-ray diffraction, and single crystal X-ray diffraction. Coordination
environments around the metal centers and subtle differences in weak
interactions affect the dimensionality and features of supramolecular
architectures of these complexes. In the case of M­(II) complexes of L1H, 1 shows a zigzag 3D architecture, whereas
other complexes exhibit 3D channel-like structures containing the
coordinated pyridine rings inside these channels. The coordination
environments around the M­(II) centers are the same in the complexes 5 and 7; however, the former is composed of 3D
architecture containing channels and voids, whereas the latter reveals
a 2D sheet structure. The 3D supramolecular architecture of complex 6 is sustained by helical channels, which are filled by lattice
water and pyridine molecules. Solid state fluorescence emission properties
of L1H and its M­(II) complexes show resemblance to each
other, whereas they have different characteristics in the case of L2H and its M­(II) complexes. Cyclic voltammetry of redox-active
ligand L2H and its complexes 5 and 6 are also studied.