Consequence of Presence and Absence of π-Clouds at Strategic Locations of Designed Binuclear Pd(II) Complexes on Packing: Self-Assembly of Self-Assembly by Intermolecular Locking and Packing

Abstract

Self-assembled binuclear coordination cages of general formula [Pd2(N–N)2(L)2](X)4, 1a/b–4a/b are prepared by the combination of N,N′-bis(m-pyridyl)urea, L, with a variety of cis-protected palladium(II) components, Pd(N–N)(X)2. The cis-protecting units “N–N” employed for the synthesis of 1–4 are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), respectively. The term “X” stands for nitrate and perchlorate for a and b, respectively. The assemblies are characterized by NMR and electrospray ionization mass spectrometry (ESI-MS) techniques, and in some cases (i.e., 1a, 2b, 3b, 4a, and 4b) the structures are confirmed by single crystal X-ray diffraction. The conformations of bound L in the crystal structures of all the Pd(II) complexes are found to be syn-syn. The influence of the presence and absence of π cloud at the cis-protecting units on the crystal packing has been studied in detail. In the packing of [Pd2(phen)2 L 2](NO3)4, 4a, one unit of [Pd2(phen)2 L 2]4+ is associated with two other units by π–π stacking interactions thus giving a one-dimensional growth as envisioned on the basis of a design principle. In the case of [Pd2(en)2(L) 2](NO3)4, 1a, and [Pd2(tmeda)2(L)2](ClO4)4, 2b, such packing is not observed due to the absence of π-cloud at the strategic locations, instead notable H-bonding interactions are seen. However, [Pd2(bpy)2(L)2](ClO4)4, 3b, displays a π–π interactions using only two units of [Pd2(bpy)2(L)2]4+(ClO4)−.

Reversible Mechanical Interlocking of D‐Shaped Molecular Karabiners bearing Coordination‐Bond Loaded Gates: Route to Self‐Assembled [2]Catenanes

“…The phenylene protons (H d ) are located at 7.97 ppm, having shifted upfield by 0.09 ppm whereas, the methylene protons (H c ) appear at 5.87 ppm, with upfield shift of 0.07 ppm relative to uncomplexed ligand L1 . The peaks of the protons present in the cis ‐protecting moieties, that is, en, tmeda, bpy, and phen in 1 a – d are located in the expected positions 17a–b. 25…”

Structural and Dynamic Aspects of Palladium(II)‐Based Self‐Assembled Binuclear Coordination Complexes

“…The shape of complexes with Pd 2 L′ 2 L 2 composition is varied (e. g. plateau, steps, bow‐shaped, opened jaws, zigzag plateau, and helicates) due to the inherent conformational mobilities,, whereas the shape of complexes with Pd 2 L 4 composition is limited to helical or non‐helical types ,,. Although a variety of ligands are used for the preparation of such complexes, the use of urea functionality in the ligand back‐bone is uncommon, in literature.…”

Octadecanuclear Gear Wheels by Self‐Assembly of Self‐Assembled “Double Saddle”‐Type Coordination Entities: Molecular “Rangoli”

“…[1] In order to describe the composition of the core of the architectures, such complexes could be classified under [Pd x L' x L y ] families. A large number of binuclear [Pd 2 L' 2 L 2 ]-type complexes have been prepared, [1][2][3][4][5][6] mostly from selected "bow-shaped" non-chelating bidentate ligands and a variety of cis-protected palladium(II) compounds. Well-explored functional and structural aspects of these binuclear complexes include guest encapsulation, [2] interlocking to form [2]-catenanes, [3] and solid-state packing.…”

“…Well-explored functional and structural aspects of these binuclear complexes include guest encapsulation, [2] interlocking to form [2]-catenanes, [3] and solid-state packing. [4,5] In such binuclear complexes, there are two square-planar palladium(II) centers, in which both of the coordination square planes are usually located almost in the same plane, in a "plateau"-type overall disposition. [5] Considerably fewer [Pd 2 L' 2 L 2 ]-type compounds prepared from slightly divergent "U-shaped" ligands have been reported, in which one of the square planes is radially displaced from the plateau position and located almost above the other in an "opened jaws" manner ( Figure 1 a).…”

“…[5] Considerably fewer [Pd 2 L' 2 L 2 ]-type compounds prepared from slightly divergent "U-shaped" ligands have been reported, in which one of the square planes is radially displaced from the plateau position and located almost above the other in an "opened jaws" manner ( Figure 1 a). [4,6] A series of self-assembled "opened jaws"-shaped compounds have been studied in our group to evaluate their packing in the solid state and to effect targeted self-assembly of the self-assembled complexes. [4] Herein, we report trinuclear "double saddle"-type complexes of a new architecture (Figure 1 c) with [Pd 3 L' 3 L 2 ] formulation.…”