Double Level Selection in a Constitutional Dynamic Library of Coordination Driven Supramolecular Polygons

Synthesis, Structural, and Cytotoxic Properties of New Water-Soluble Copper(II) Complexes based on 2,9-Dimethyl-1,10-Phenanthroline and Their One Derivative Containing 1,3,5-Triaza-7-Phosphaadamantane-7-Oxide

A series of water-soluble copper(II) complexes based on 2,9-dimethyl-1,10-phenanthroline (dmphen) and mixed-ligands, containing PTA=O (1,3,5-triaza-7-phosphaadamantane-7-oxide) have been synthesized and fully characterized. Two types of complexes have been obtained, monocationic [Cu(NO₃)(O-PTA=O)(dmphen)][PF₆] (1), [Cu(Cl)(dmphen)₂][PF₆] (2), and neutral [Cu(NO₃)₂(dmphen)] (3). The solid-state structures of all complexes have been determined by single-crystal X-ray diffraction. Magnetic studies for the complex 1–3 indicated a very weak antiferromagnetic interaction between copper(II) ions in crystal lattice. Complexes were successfully evaluated for their cytotoxic activities on the normal human dermal fibroblast (NHDF) cell line and the antitumor activity using the human lung carcinoma (A549), epithelioid cervix carcinoma (HeLa), colon (LoVo), and breast adenocarcinoma (MCF-7) cell lines. Complexes 1 and 3 revealed lower toxicity to NHDF than A549 and HeLa cells, meanwhile compound 2 appeared to be more toxic to NHDF cell line in comparison to all cancer lines. Additionally, interactions between the complexes and human apo-transferrin (apo-Tf) using fluorescence and circular dichroism (CD) spectroscopy were also investigated. All compounds interacted with apo-transferrin, causing same changes of the protein conformation. Electrostatic interactions dominate in the 1/2 – apo- Tf systems and hydrophobic and ionic interactions in the case of 3.

A Zn(II) Metallocycle as Platform to Assemble a 1D + 1D → 1D Polyrotaxane via π···π Stacking of an Ancillary Ligand

A new [Zn2L2] metallocycle bearing two metal centers that can coordinate ancillary ligands and a pocket suitable to host guest molecules is reported. These two features are exploited by reacting the metallocycle with a pyridine ligand to self-assemble in the solid state an extended intertwined system with the rare 1D + 1D → 1D topology. This interpenetrated architecture is supported by π···π stacking between two pyridine units of two different metallocycles in the pocket of a third metallocycle.

Metallosupramolecular Architectures of Ambivergent Bis(Amino Acid) Biphenyldiimides

The metallosupramolecular chemistry of two enantiopure dicarboxylate ligands has been explored for their potential to form discrete or polymeric interlocked motifs. Consequently, both discrete and polymeric supramolecular complexes have been synthesised, yielding M₂ L₂ metallomacrocycles (1 and 2), a heteroleptic M₂ L₃ metallomacrobicycle (3), a non-interpenetrated coordination polymer (4), and highly unusual chiral M₈ L₈ squares (5 and 6). There appears to be a preference for the ligands to form M₂ L₂ -type metallomacrocyclic structural units (which feature in 1-4), although these do not engage in any mechanical interlocking, which is perhaps a combined function of the ligand flexibility and relatively small pi-surface contrasted to previous analogues. Using copper paddlewheel SBUs, chiral double-walled squares (5 and 6) are formed with large internal cavities yet poor stabilities, unexpectedly featuring the paddlewheel motifs at the vertices of the polygonal complex.

Palladium(II)-Based Self-Assembled Heteroleptic Coordination Architectures: A Growing Family

Metal-driven self-assembly is one of the most effective approaches to lucidly design a large range of discrete 2D and 3D coordination architectures/complexes. Palladium(II)-based self-assembled coordination architectures are usually prepared by using suitable metal components, in either a partially protected form (PdL') or typical form (Pd; charges are not shown), and designed ligand components. The self-assembled molecules prepared by using a metal component and only one type of bi- or polydentate ligand (L) can be classified in the homoleptic series of complexes. On the other hand, the less explored heteroleptic series of complexes are obtained by using a metal component and at least two different types of non-chelating bi- or polydentate ligands (such as L^a and L^b ). Methods that allow the controlled generation of single, discrete heteroleptic complexes are less understood. A survey of palladium(II)-based self-assembled coordination cages that are heteroleptic has been made. This review article illustrates a systematic collection of such architectures and credible justification of their formation, along with reported functional aspects of the complexes. The collected heteroleptic assemblies are classified here into three sections: 1) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal; 2) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is different; and 3) [Pd_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal. Representative examples of some important homoleptic architectures are also provided, wherever possible, to set a background for a better understanding of the related heteroleptic versions. The purpose of this review is to pave the way for the construction of several unique heteroleptic coordination assemblies that might exhibit emergent supramolecular functions.

A Cu(ii) metallocycle for the reversible self-assembly of coordination-driven polyrotaxane-like architectures

We report the design and synthesis of a Cu(ii) metallocycle (1) and use the possibility to expand the Cu(ii) coordination sphere to self-assemble mechanically interlocked species via interpenetration. Metallocycle 1 can be used as a platform to reversibly assemble a 1D + 1D → 1D coordination-driven polyrotaxane (3), where 1 acts as the hosting ring as well as the stopper, and 4,4'-bipyridine is the guest-axle. A coordinating solvent can substitute the 4,4'-bipyridine axle to disassemble the polyrotaxane (3 → 2) that is easily restored by further adding 4,4'-bipyridine (2 → 3). Other polyrotaxanes can be isolated by reacting 1 with pyridine (4) and phenylpyridine (5). Interconversion among the presented species is demonstrated and ensured by the open position of each copper center in platform 1.

Diversity of metal-organic macrocycles assembled from carbazole based ligands with different lengths

A series of carbazole based ligands with different lengths were assembled with nickel ions to construct metal-organic macrocycles. High-resolution mass spectrometry and ion mobility-mass spectrometry have been used to analyse the resulting M_nL_n assembly coexisting in solution. Combining with the structural analysis of their solid confirmation, it was revealed that the diversity of the metal-organic macrocycles was increased with the flexibility of the ligands.

The electronic properties of three popular high spin complexes [TM(acac)3, TM = Cr, Mn, and Fe] revisited: an experimental and theoretical study

The occupied and unoccupied electronic structures of three high spin TM(acac)₃ (TM = Cr, Mn, and Fe) complexes (I, II, and III, respectively) were studied by revisiting their literature vapour-phase He(i) and, when available, He(ii) photoemission (PE) spectra and by means of original near-edge X-ray absorption fine structure (NEXAFS) spectroscopic data recorded at the O K-edge (^OK-edge) and TM L_2,3-edges (^TML_2,3-edges). The assignments of the vapour-phase He(i)/He(ii) PE spectra were guided by the results of spin-unrestricted non-relativistic Slater transition state calculations, while the ^OK-edge and ^TML_2,3-edge spectroscopic pieces of evidence were analysed by exploiting the results of spin-unrestricted scalar-relativistic time-dependent density functional theory (DFT) and DFT/ROCIS calculations, respectively. Although the actual symmetry (D₃, in the absence of any Jahn-Teller distortion) of the title molecules allowed an extensive mixing between TM t_2g-like and e_g-like atomic orbitals, the use of the Nalewajski-Mrozek TM-O bond multiplicity index combined with a thorough analysis of the ground state (GS) outcomes allowed the assessment of the TM-O bond weakening associated with the progressive TM 3d-based e_g-like orbital filling. The experimental information provided by ^OK-edge spectra was rather poor; nevertheless, the combined use of symmetry, orbitals and spectra allowed us (i) to rationalise minor differences characterizing spectral features along the series, (ii) to quantify the contribution provided by the ligand-to-metal-charge-transfer (LMCT) excitations to the different spectral features, and (iii) to recognize the t_2g-/e_g-like nature of the TM 3d-based orbitals involved in LMCT transitions. As far as the ^TML_2,3-edge spectra and the DFT/ROCIS results were concerned, the lowest lying I^,IIL₃ spectral features included states having either the GS spin multiplicity (S(I) = 3/2, S(II) = 2) or, at higher excitation energies (EEs), states with ΔS = ±1. In contrast to that, only states with ΔS = 0, -1 significantly contributed to the IIIL₃ spectral pattern. Along the whole series, the L₃ higher EE side was systematically characterized by states involving ^TM2p → π₄ MLCT excitations; as such, coupled-single excitations with ΔS = 0 were involved in I and II, while single MLCT ^TM2p → π₄ transitions with ΔS = -1 were involved in III.

Open and closed forms of the interpenetrated [Cu2(Tae)(Bpa)2](NO3)2·nH2O: magnetic properties and high pressure CO2/CH4 gas sorption

Two closed and one open structural forms of the interpenetrated [Cu₂(Tae)(Bpa)₂](NO₃)₂·nH₂O (H₂Tae = 1,1,2,2-tetraacetylethane, Bpa = 1,2-bis(4-pyridyl)ethane) cationic coordination polymer have been synthesized. Three crystallographically related interpenetrated "ths" cationic nets encapsulate water molecules and nitrate anions giving rise to the closed structural forms of [Cu₂(Tae)(Bpa)₂](NO₃)₂·nH₂O. Depending on the location of water molecules and nitrate groups, two different closed forms with 5.5 and 3.6 crystallization water molecules have been obtained. The thermal activation of the closed structures gives rise to a 29% expansion of the unit cell. This closed to open transformation is reversible, and is triggered by the loss or uptake of solvent. The high pressure gas adsorption experiments show similar selectivity values towards CO₂ for CO₂/CH₄ mixtures to that showed by some metal organic frameworks without unsaturated metal sites, and isosteric heats for CO₂ adsorption similar to that for the HKUST-1 compound.

Amplification of a metallacyclic receptor out of a dynamic combinatorial library

We present herein the Pt(ii)-directed self-assembly in water of a new conformationally flexible N-monoalkyl-4,4-bipyridinium-based ditopic ligand into a library of six different metallacyclic structures.

Metal-Ligand Exchange in a Cyclic Array: The Stepwise Advancement of Supramolecular Complexity

Herein, we demonstrate how the supramolecular complexity (evaluated by the degree of self-sorting M) evolves in a chemical cycle of cascaded metallosupramolecular transformations, using abiological self-assembled entities as input signals. Specifically, the successive addition of the supramolecular self-assembled structures S1 and (T2 + S2) to the starting supramolecular two-component equilateral triangle T1 (M = 1) first induced a fusion into the three-component quadrilateral R1 (M = 6) and then to the five-component scalene triangle T3 (M = 16). Upon the addition of the supramolecular input M1 to T3, a notable self-sorting event occurred, leading to regeneration of the triangle T1 along with formation of the scalene triangle T4 (M = 25). This last step closed the cycle of the supramolecular transformations.

Supramolecular transformations within discrete coordination-driven supramolecular architectures

In this review, a comprehensive summary of supramolecular transformations within discrete coordination-driven supramolecular architectures, including helices, metallacycles, metallacages, etc., is presented.

Theoretical modeling of the L2,3-edge X-ray absorption spectra of Mn(acac)2 and Co(acac)2 complexes

Mn(acac)₂ and Co(acac)₂ L_2,3-edge spectra were successfully modeled by the DFT/ROCIS method. Both Mn(ii) and Co(ii) have a distorted tetrahedral environment and, similarly to other M(ii) complexes, the higher EE side of L₃ and L₂ includes states, which involve MLCT transitions.

Electronic structures of CuTPP and CuTPP(F) complexes. A combined experimental and theoretical study I

CuTPP and CuTPP(F) core levels and valence band states are consistently investigated in great detail.

Electronic structure of CuTPP and CuTPP(F) complexes: a combined experimental and theoretical study II

CuTPP and CuTPP(F) thick films deposited on Au(111) have been studied by coupling NEXAFS spectroscopy at the ^C/N/FK-edges and ^CuL_2,3-edges and spin-unrestricted TD-DFT calculations.

Post-assembly guest oxidation in a metallo-supramolecular host and structural rearrangement to a coordination polymer

PTA hosted in a copper metallo-supramolecular triangle undergoes post-assembly oxidation to form PTAO in aerated solutions. The oxidation is triggered by selected co-solvents that also govern the formation of the final crystalline product leading to a discrete host-guest triangle {PTAO@[Cu(o-L)]3} or to a 1D coordination polymer {(PTAO)2@[Cu8][Cu2]}∞ containing a {Cu8} ring with a double hosting pocket.