Multi-Stimuli-Responsive Metallogel Molded from a Pd₂<b>L</b>₄‑Type Coordination Cage: Selective Removal of Anionic Dyes

A self-assembled binuclear coordination cage of the Pd₂<b>L</b>₄ formulation has been constructed by complexation of Pd­(NO₃)₂ with <i>N</i>,<i>N</i>′-bis­(3-pyridylmethyl)­naphthalenediimide (<b>L</b>). The cage, i.e., [Pd₂(<b>L</b>)₄]­(NO₃)₄ (<b>1</b>), displayed a further self-assembly phenomenon to afford a gel phase, upon dissolution in either dimethyl sulfoxide or acetonitrile–water (1:1) followed by standing at room temperature. It was observed that a synergy among the metal ion, ligand, counteranion, solvent, and concentration played a vital role for metallogel formation. The morphology of the metallogel as observed from microscopy studies revealed the formation of a rare variety of nanoscale metal–organic particles. Salient features of the gel include the thixotropic (mechanoresponsive) nature, in addition to the reversible chemical-stimuli-responsive behavior. The presence of naphthalenediimide moieties at the backbone of the cage and the cationic nature of the cavity of the cage could be exploited to study the functional aspects of the gel. The porous gel exhibited the abilities to uptake pyrene as a guest and to selectively remove anionic dyes from aqueous solutions. The gel could bind representative anionic dyes like “acid blue 93” and “methyl orange” in the absence or presence of certain cationic dyes, making the material suitable for selective dye removal applications

Toppled Molecular-Domino Sets by Self-Assembly of Self-assembly: The π‑Polymers

A series of designed binuclear palladium­(II)-based self-assemblies, [Pd₂­(en)₂­(<b>L</b>)₂]­(NO₃)₄, <b>1a</b>; [Pd₂­(tmeda)₂­(<b>L</b>)₂]­(NO₃)₄, <b>2a</b>; [Pd₂­(bpy)₂­(<b>L</b>)₂]­(NO₃)₄, <b>3a</b>; and [Pd₂­(phen)₂­(<b>L</b>)₂]­(NO₃)₄, <b>4a</b>, are synthesized. These complexes are obtained in good to excellent yields by equimolar combination of the nonchelating bidentate ligand bis­(4-pyridyl­methyl)­piperazine, <b>L</b>, with the corresponding <i>cis</i>-protected palladium­(II) component, that is, Pd­(N-N)­(NO₃)₂, under suitable reaction conditions. The <i>cis</i>-protecting N-N units used are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridyl (bpy), and 1,10-phenanthroline (phen). The complexes <b>1a</b>–<b>4a</b> are well-characterized by ¹H NMR, H–H COSY, and HSQC, and the molecular compositions have been established by ESI-MS. The molecular structures are confirmed for the complexes [Pd₂­(tmeda)₂­(<b>L</b>)₂]­(ClO₄)₄, <b>2b</b>; [Pd₂­(bpy)₂­(<b>L</b>)₂]­(ClO₄)₄, <b>3b</b>; and [Pd₂­(phen)₂­(<b>L</b>)₂]­(NO₃)₄, <b>4a</b>, by the single-crystal X-ray diffraction technique. In the cases of the complexes <b>3b</b> and <b>4a</b>, the crystal packing diagrams display a unique one-dimensional predefined organization of molecules by intermolecular π–π interactions using the strategically located π-surfaces of the <i>cis</i>-protecting units. This organization resembles a set of toppled dominos. A given set exhibits further interactions with the neighboring sets in the packing pattern that are influenced by the nature of the N-N moiety, for example, bpy or phen. However, no such arrangement is observed in the case of the complex <b>2b</b> due to the lack of a π-surface at the <i>cis</i>-protecting moiety

Trinuclear <i>Intro-Vertere</i> Circular Helicate and Its Columnar Hexagonal Stacking

A self-assembled discrete Pd₃L′₃L₃ type circular helicate of hitherto unknown architecture is disclosed in this work where L′ stands for 1,10-phenanthroline (phen) and L for a triazole appended bidentate nonchelating ligand, i.e., 1,4-bis­((1<i>H</i>-1,2,3-triazol-1-yl)­methyl)­benzene. The coordination environment of palladium­(II) in any given PdN₄ coordination planes of the helicate is described by one phen moiety and two triazole moieties belonging to different ligand strands. All the three bound phen moieties are uniquely turned inside and lodged in the internal cavity of the molecule; hence the term “<i>intro-vertere</i> circular helicate” is introduced. One of the PdN₄ square planes is sandwiched between the other two via phen-inspired intramolecular π-stacking making a cylindrical stacking arrangement. A racemic pair designated as <i>MPP</i> and <i>PMM</i> isomers, where <i>M</i> and <i>P</i> stand for the handedness of the ligand L, is observed in the crystal structure. In the crystal packing, the trinuclear <i>intro-vertere</i> circular helicate molecules are arranged in a columnar hexagonal stacking. The two exposed phen moieties of a given molecule participated in the intermolecular π-stacking. The <i>MPP</i> and <i>PMM</i> isomers are arranged in an alternate manner in the stacks

Double-Stranded Binuclear Helicates and Helicity Modulation

All of the reported self-assembled complexes of <i>cis</i>-Pd₂L′₂L₂ formulation, where L′ stands for a chelating bidentate ligand and L for a nonchelating bidentate ligand, are “non-helical”. We disclose here the debut of the long awaited “helicate” type architecture of the <i>cis-</i>Pd₂L′₂L₂ formulation. In the present work, the term L′ stands for tetramethylethylenediamine (<i>tmeda</i>) and L stands for a (1<i>H</i>-imidazolyl)­methyl-appended bidentate nonchelating ligand having a rigid spacer. The torsion angle between the two coordination PdN₄ planes of a given “helicate” is considered here as its magnitude of helicity. Length of spacer unit (i.e., 1,4-benzene, 4,4′-biphenyl and 4,4′-<i>p</i>-terphenyl) crafted in the backbone of L is found to impart such conformation to the bound ligand moieties that the magnitude of helicity is modulated

Self-Assembled Molecular Squares as Supramolecular Tectons

Concentration-dependent equilibria of molecular squares [Pd₄(L′)₄(L)₄]­(NO₃)₈ and triangles [Pd₃(L′)₃(L)₃]­(NO₃)₆ were obtained when cis-protected Pd­(II) units [PdL′(NO₃)₂] (L′ = tmeda, 2,2′-bpy, and phen) were combined independently with 4,4′-bipyridine (L) in water. However, complexation of [PdL′(OTs)₂] with L resulted in exclusive formation of the corresponding molecular squares. The addition of AgOTs to each mixture of square and triangle led to a shift in the equilibrium, resulting in the disappearance of the triangles and exclusive formation of the corresponding squares. The crystal structures of the molecular squares [Pd₄(L′)₄(L)₄]­(OTs)₈ revealed a pair of tosylate anions encapsulated in the hydrophobic cavity of the square. Further, [Pd₄(2,2′-bpy)₄­(L)₄]­(OTs)₈ and [Pd₄(phen)₄(L)₄]­(OTs)₈ exhibited solvatomorphism, yielding two crystalline forms each, respectively. The cationic units in these crystals associate through intermolecular π<b>···</b>π stacking interactions wherein the cis-protecting units (i.e., 2,2′-bpy and phen) of adjacent molecules overlap via side-on or end-on modes. Thus, the cations may be considered as “tectons”, each of which contains four peripheral 2,2′-bpy/phen units, which behave as “supramolecular synthons” in the self-assembly of the squares. The tosylates interact with the cations through C–H<b>···</b>O and C–H<b>···</b>π interactions and play a role in the packing of the molecular squares

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

Self-assembled binuclear coordination cages of general formula [Pd₂(N–N)₂(<b>L</b>)₂]­(X)₄, <b>1a/b</b>–<b>4a/b</b> are prepared by the combination of <i>N</i>,<i>N</i>′-bis­(<i>m</i>-pyridyl)­urea, <b>L</b>, with a variety of <i>cis</i>-protected palladium­(II) components, Pd­(N–N)­(X)₂. The <i>cis</i>-protecting units “N–N” employed for the synthesis of <b>1</b>–<b>4</b> are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), respectively. The term “X” stands for nitrate and perchlorate for <b>a</b> and <b>b</b>, respectively. The assemblies are characterized by NMR and electrospray ionization mass spectrometry (ESI-MS) techniques, and in some cases (i.e., <b>1a</b>,<b> 2b</b>,<b> 3b</b>,<b> 4a</b>, and <b>4b</b>) the structures are confirmed by single crystal X-ray diffraction. The conformations of bound <b>L</b> in the crystal structures of all the Pd­(II) complexes are found to be <i>syn-syn</i>. The influence of the presence and absence of π cloud at the <i>cis-</i>protecting units on the crystal packing has been studied in detail. In the packing of [Pd₂(phen)₂<b>L</b>₂]­(NO₃)₄, <b>4a</b>, one unit of [Pd₂(phen)₂<b>L</b>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(<b>L)</b>₂]­(NO₃)₄, <b>1a</b>, and [Pd₂(tmeda)₂(<b>L</b>)₂]­(ClO₄)₄, <b>2b</b>, 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(<b>L</b>)₂]­(ClO₄)₄, <b>3b</b>, displays a π–π interactions using only two units of [Pd₂(bpy)₂(<b>L</b>)₂]⁴⁺(ClO₄)⁻

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

Self-assembled binuclear coordination cages of general formula [Pd₂(N–N)₂(<b>L</b>)₂]­(X)₄, <b>1a/b</b>–<b>4a/b</b> are prepared by the combination of <i>N</i>,<i>N</i>′-bis­(<i>m</i>-pyridyl)­urea, <b>L</b>, with a variety of <i>cis</i>-protected palladium­(II) components, Pd­(N–N)­(X)₂. The <i>cis</i>-protecting units “N–N” employed for the synthesis of <b>1</b>–<b>4</b> are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), respectively. The term “X” stands for nitrate and perchlorate for <b>a</b> and <b>b</b>, respectively. The assemblies are characterized by NMR and electrospray ionization mass spectrometry (ESI-MS) techniques, and in some cases (i.e., <b>1a</b>,<b> 2b</b>,<b> 3b</b>,<b> 4a</b>, and <b>4b</b>) the structures are confirmed by single crystal X-ray diffraction. The conformations of bound <b>L</b> in the crystal structures of all the Pd­(II) complexes are found to be <i>syn-syn</i>. The influence of the presence and absence of π cloud at the <i>cis-</i>protecting units on the crystal packing has been studied in detail. In the packing of [Pd₂(phen)₂<b>L</b>₂]­(NO₃)₄, <b>4a</b>, one unit of [Pd₂(phen)₂<b>L</b>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(<b>L)</b>₂]­(NO₃)₄, <b>1a</b>, and [Pd₂(tmeda)₂(<b>L</b>)₂]­(ClO₄)₄, <b>2b</b>, 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(<b>L</b>)₂]­(ClO₄)₄, <b>3b</b>, displays a π–π interactions using only two units of [Pd₂(bpy)₂(<b>L</b>)₂]⁴⁺(ClO₄)⁻

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

Self-assembled binuclear coordination cages of general formula [Pd₂(N–N)₂(<b>L</b>)₂]­(X)₄, <b>1a/b</b>–<b>4a/b</b> are prepared by the combination of <i>N</i>,<i>N</i>′-bis­(<i>m</i>-pyridyl)­urea, <b>L</b>, with a variety of <i>cis</i>-protected palladium­(II) components, Pd­(N–N)­(X)₂. The <i>cis</i>-protecting units “N–N” employed for the synthesis of <b>1</b>–<b>4</b> are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), respectively. The term “X” stands for nitrate and perchlorate for <b>a</b> and <b>b</b>, respectively. The assemblies are characterized by NMR and electrospray ionization mass spectrometry (ESI-MS) techniques, and in some cases (i.e., <b>1a</b>,<b> 2b</b>,<b> 3b</b>,<b> 4a</b>, and <b>4b</b>) the structures are confirmed by single crystal X-ray diffraction. The conformations of bound <b>L</b> in the crystal structures of all the Pd­(II) complexes are found to be <i>syn-syn</i>. The influence of the presence and absence of π cloud at the <i>cis-</i>protecting units on the crystal packing has been studied in detail. In the packing of [Pd₂(phen)₂<b>L</b>₂]­(NO₃)₄, <b>4a</b>, one unit of [Pd₂(phen)₂<b>L</b>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(<b>L)</b>₂]­(NO₃)₄, <b>1a</b>, and [Pd₂(tmeda)₂(<b>L</b>)₂]­(ClO₄)₄, <b>2b</b>, 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(<b>L</b>)₂]­(ClO₄)₄, <b>3b</b>, displays a π–π interactions using only two units of [Pd₂(bpy)₂(<b>L</b>)₂]⁴⁺(ClO₄)⁻

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

Self-assembled binuclear coordination cages of general formula [Pd₂(N–N)₂(<b>L</b>)₂]­(X)₄, <b>1a/b</b>–<b>4a/b</b> are prepared by the combination of <i>N</i>,<i>N</i>′-bis­(<i>m</i>-pyridyl)­urea, <b>L</b>, with a variety of <i>cis</i>-protected palladium­(II) components, Pd­(N–N)­(X)₂. The <i>cis</i>-protecting units “N–N” employed for the synthesis of <b>1</b>–<b>4</b> are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), respectively. The term “X” stands for nitrate and perchlorate for <b>a</b> and <b>b</b>, respectively. The assemblies are characterized by NMR and electrospray ionization mass spectrometry (ESI-MS) techniques, and in some cases (i.e., <b>1a</b>,<b> 2b</b>,<b> 3b</b>,<b> 4a</b>, and <b>4b</b>) the structures are confirmed by single crystal X-ray diffraction. The conformations of bound <b>L</b> in the crystal structures of all the Pd­(II) complexes are found to be <i>syn-syn</i>. The influence of the presence and absence of π cloud at the <i>cis-</i>protecting units on the crystal packing has been studied in detail. In the packing of [Pd₂(phen)₂<b>L</b>₂]­(NO₃)₄, <b>4a</b>, one unit of [Pd₂(phen)₂<b>L</b>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(<b>L)</b>₂]­(NO₃)₄, <b>1a</b>, and [Pd₂(tmeda)₂(<b>L</b>)₂]­(ClO₄)₄, <b>2b</b>, 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(<b>L</b>)₂]­(ClO₄)₄, <b>3b</b>, displays a π–π interactions using only two units of [Pd₂(bpy)₂(<b>L</b>)₂]⁴⁺(ClO₄)⁻

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

Self-assembled binuclear coordination cages of general formula [Pd₂(N–N)₂(<b>L</b>)₂]­(X)₄, <b>1a/b</b>–<b>4a/b</b> are prepared by the combination of <i>N</i>,<i>N</i>′-bis­(<i>m</i>-pyridyl)­urea, <b>L</b>, with a variety of <i>cis</i>-protected palladium­(II) components, Pd­(N–N)­(X)₂. The <i>cis</i>-protecting units “N–N” employed for the synthesis of <b>1</b>–<b>4</b> are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), respectively. The term “X” stands for nitrate and perchlorate for <b>a</b> and <b>b</b>, respectively. The assemblies are characterized by NMR and electrospray ionization mass spectrometry (ESI-MS) techniques, and in some cases (i.e., <b>1a</b>,<b> 2b</b>,<b> 3b</b>,<b> 4a</b>, and <b>4b</b>) the structures are confirmed by single crystal X-ray diffraction. The conformations of bound <b>L</b> in the crystal structures of all the Pd­(II) complexes are found to be <i>syn-syn</i>. The influence of the presence and absence of π cloud at the <i>cis-</i>protecting units on the crystal packing has been studied in detail. In the packing of [Pd₂(phen)₂<b>L</b>₂]­(NO₃)₄, <b>4a</b>, one unit of [Pd₂(phen)₂<b>L</b>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(<b>L)</b>₂]­(NO₃)₄, <b>1a</b>, and [Pd₂(tmeda)₂(<b>L</b>)₂]­(ClO₄)₄, <b>2b</b>, 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(<b>L</b>)₂]­(ClO₄)₄, <b>3b</b>, displays a π–π interactions using only two units of [Pd₂(bpy)₂(<b>L</b>)₂]⁴⁺(ClO₄)⁻