Advances on supramolecular assembly of cyclometalated platinum(Ⅱ) complexes

Organoplatinum(Ⅱ) compounds have received enormous attention over the past decades due to their square-planar geometry as well as intriguing photo-physical properties.Self-assembly has emerged as an excellent approach to create well-ordered supramolecular architectures with tunable properties,which underpin the role of solvent-directed approach for the design of functional materials.In this minireview,the recent advances on supramolecular self-assembly of cyclometalated platinum(Ⅱ) complexes have been discussed.During the self-assembly process,non-covalent Pt-Pt and π-π interactions play crucial roles in controlling the structures and functions of the resulting assemblies.     

A novel dinuclear double-stranded helical complexes of bis(terdentate) N4O2 donor ligand with silver(I) and zinc(II) d metal ions

Reaction of the hexadentate N₄O₂-donor ligand 6,6′-bis(3-hydrazonobutan-2-one)-2,2′-bipyridine (L) with Ag^(I) and Zn^(II) affords a dinuclear double stranded helicate species [Ag₂L₂]²⁺ (1a) and [Zn₂L₂]²⁺ (1b), in which partitioning of the ligand into two bis-tridentate pyridyl-ketoimine chelating units allow each ligand to bridge both metal centres. X-ray crystallography, ESI-MS and UV–Vis spectrophotometric titration experiments reveal that the complex (1a) retains its solid-state structure in solution. The crystal structure of (1a) provides the first example of dinuclear silver(I) complex in which both of the metal centres can be approximated as a seven coordinate distorted mono-capped trigonal prism in which the Ag?Ag close contact of 3.034(4) Å is taken into account and forms the cap. The counter-ions do not interact with metal centres but hydrogen bond to N–H protons of the hydrazonic arms from the separate strands. The adjacent helical units are cross-linked together via NH?O_keto hydrogen bonding to maintain the supramolecular structure.     

Self-assembly of supramolecular Ni(II) and Cu(II) metalmacrocyclic compounds with tetraazamacrocyclic ligand into a gelatin-immobilized matrix

Self-assembly in M(II)-ethanedithioamide [H₂N–C(=S)–C(=S)–NH₂]-propanone triple systems (M=Ni, Cu) into corresponding metal(II) hexacyanoferrate(II) gelatin-immobilized matrix systems under contact with aqueous-alkaline (pH?～?12) solutions containing ethanedithioamide and propanone have been studied. Formation of supramolecular macrotetracyclic compounds of Ni(II) and Cu(II) with 2,7,7,9,14,14-hexamethyl-3,6,10,13-tetraazacyclotetradecadien-2,9-tetrathione-4,5,11,12 containing original “kernel” (metal complex) and “shell” surrounding this “kernel”, of polypeptide chains of the gelatin molecules, occurs under such specific conditions.     

Ligand Self-Recognition in the Self-Assembly of a [{Cu(L)}2]2+ Complex: The Role of Chirality

The chirality alone of a conformationally restricted, bifunctional ligand (L) is the basis for the self-recognition process schematically represented below. A racemic mixture of these ligands reacts with Cu⁺ ions quantitatively to generate a racemic mixture of a [(CuL)₂]²⁺ homochiral complex (represented by cubes), where each complex contains ligands with identical configurations.     

Salen-type nickel(II), palladium(II) and copper(II) complexes having chiral and racemic camphoric diamine components

Chiral and racemic Salen-type Schiff-base ligands (H₂L¹, H₂L² and H₂L³), condensed between D-(+)- and D,L-camphoric diamine (also known as (1R,3S)-1,2,2-trimethylcyclopentane-1,3-diamine) and 2-hydroxybenzaldehyde or 3,5-dibromo-2-hydroxybenzaldehyde with a 1:2 molar ratio, have been synthesized and characterized. A series of new nickel(II), palladium(II) and copper(II) complexes of these chiral and racemic ligands exhibiting different coordination number (4, 5 and 6) have been characterized with the formulae [NiL¹]·CH₃OH (3), [NiL¹]·H₂O (4), [NiL²] (5), [PdL²] (6), [Cu₂(L²)₂(H₂O)] (7) and [NiL³(DMF)(H₂O)] (8). Different solvent molecules in 3 and 4 (methanol and water molecules) as well as different apical ligands in 7 and 8 (water and DMF molecules) are involved in different O–H···O hydrogen bonding interactions to further stabilize the structures. UV–Vis (UV–Vis), circular dichroism (CD) spectra and thermogravimetric (TG) analyses for the metal complexes have also been carried out.     

Self-assembly of iron TCPP (meso-tetra(4-carboxyphenyl)porphyrin) into a chiral 2D coordination polymer

Synthetic metalloporphyrin complexes are often used as analogues of natural systems, and they can be used for the preparation of high-dimensional coordination polymers. In this work, a new chiral Fe-TCPP (TCPP is meso-tetra-(4-carboxyphenyl)porphyrin) coordination compound has been synthesized and structurally characterized. The compound is 2D via coordination bonds, and it exhibits strong hydrogen bonds that connect the planar arrays forming the 3D framework. The oxidation of the original Fe^II ions to Fe^III accounts for the formation of this array, in which the topological analysis reveals a very high connectivity based on a simple extension fashion of the structure. DFT calculations have been also carried out to study the stabilization of the Fe^III-compound. This is the third example of a 2D coordination compound based on TCPP in which the dimensionality refers just to coordination bonds, and no other ligands are present in the structure.     

A Schiff-base cross-linked supramolecular polymer containing diiminophenol compartments and its interaction with copper(II) ions

We report here the preparation of a Schiff-base linked organic polymer 1 based on linkages containing the potent supramolecular aggregator benzene-1,3,5-tricarboxamide, connected through 2,6-diiminophenol metal binding pockets into a cross-linked polymer. The morphological and physical properties of this material are studied using electron microscopy techniques, thermal analysis, NMR, fluorescence spectroscopy and gas adsorption studies. The interaction of the polymer 1 with Cu^II ions is then investigated by soaking the material with methanolic copper acetate solution, and studying the resulting aggregates using EDX microscopy and FTIR spectroscopy. A small-molecule model compound 2 is also prepared and crystallographically characterised to act as a spectroscopic comparison, providing strong evidence that 1 interacts with copper ions through a nucleation/seeding mechanism for the growth of microcrystalline copper acetate deposits, rather than via chemisorption of the copper ions within the diiminophenol binding pockets. Preliminary results suggest a similar mechanism for Co^II adsorption, while Zn^II ions exhibit a separate interaction mode.     

Linear polymer of a copper(II) complex and its supramolecular selectivity

The supramolecular framework [Cu₂(TU)₄?·?(TAA)₄] _n (TU?=?thiourea; TAA?=?2-(2-imino-4-oxo-5-thiazolidinylidene)acetic anion) has been synthesized by reaction of CuCl₂?·?2H₂O with meso-2,3-dibromosuccinic acid and thiourea. The one-dimensional supramolecular structure of the title complex is constructed through bridge-linkage of the S atoms on the thioureas between adjacent Cu(II) atoms, forming an infinite chain with lots of positive charges. Around the infinite chain, there are four groups of negatively charged hydrogen-bond tubes constructed by four TAA anions. The hydrogen-bond and ionic interactions between adjacent metal-organic polymeric chains and hydrogen-bond tubes form the three-dimensional supramolecular structure of the complex. Supramolecular selectivity from isomers of 2-(2-imino-4-oxo-5-thiazolidinylidene)acetic anion (TAA) has been studied by quantum calculation.     

A systematic study of ligand intermolecular interactions in crystals of copper(II) complexes of bidentate guanidino derivatives

The synthesis and X-ray structures of four neutral copper(II) complexes and one cationic complex incorporating bidentate alkyl N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)imidocarbamate ligands are reported. The neutral complexes, which possess potential doublet (DA) hydrogen bonding motifs, form supramolecular structures based on synthons involving hydrogen bonding or phenyl embraces. The formation of sheets within the crystal through combination of these synthons, and the occurrence of guest molecules trapped in cavities between the sheets, are described. The cationic complex forms an extended hydrogen-bonded structure that incorporates nitrate ions. The structures of the five complexes are compared with others reported previously for complexes of related ligands.     

Bis(2-(1H-imidazol-2-yl)-pyridine)copper(II): Effects of counteranions on the molecular and supramolecular structures

The synthesis and physical properties of bis(2-(1H-imidazol-2-yl)-pyridine)copper(II) with chloride, nitrate and perchlorate as counteranions have been described. Microanalysis, magnetic susceptibility, conductivity and various spectroscopic measurements have been used for the characterization of the complexes. The crystal structures of all three complexes have been determined. Intermolecular hydrogen-bonding interactions and the resulting self-assembly patterns for each of the species have been scrutinized. The chloride containing complex crystallizes as a trihydrate, where the metal ion is in a tetragonally elongated cis-N₄Cl₂ coordination sphere. This complex provides a three-dimensional honeycomb-like structure through N–H?Cl, O–H?Cl and O–H?O hydrogen bonds. In the nitrate containing species, one of the two counteranions coordinates to the metal centre to provide an irregular N₄O₂ coordination sphere, while the other counteranion, with the help of a lattice water molecule, assembles a ladder-like structure via N–H?O and bifurcated O–H?O,O hydrogen bonds. A one-dimensional polymeric species has been formed when perchlorate is the counteranion. Here one of the two perchlorates acts as a bridge between the metal centres that are in tetragonally elongated trans-N₄O₂ coordination spheres. This polymeric chain, together with the second perchlorate and a water molecule, form a ribbon-like structure due to N–H?O and O–H?O hydrogen bonds.     

Photofunctional supramolecular solution systems of chiral Schiff base nickel(II), copper(II), and zinc(II) complexes and photochromic azobenzenes

Preparations, crystal structures, electronic and CD spectra are reported for new chiral Schiff base complexes, bis(N-R-1-naphthylethyl-3,5-dichlorosalicydenaminato)nickel(II), copper(II), and zinc(II). Nickel(II) and copper(II) complexes adopt a square planar trans-[MN₂O₂] coordination geometry with Δ(R,R) configuration. While zinc(II) complex adopts a compressed tetrahedral trans-[MN₂O₂] one with Δ(R,R) configuration and exhibits an emission band around 21 000 cm⁻¹ (λ_ex = 27 000 cm⁻¹). Absorption and CD spectra were recorded in N,N′-dimethylformamide, acetone, methanol, chloroform, and toluene solutions to discuss relationships between spectral shifts of d–d and π–π^∗ bands by structural changes of the complexes and physical properties of the solvents. Moreover, we have attempted to investigate conformational changes of the complexes induced by photoisomerization of azobenzene, 4-hydroxyazobenzene, or 4-aminoazobenzene, in various solutions under different conditions. Weak intermolecular interactions between complexes and azobenzenes are important for the phenomenon by conformational changes of bulky π-conjugated moieties of the ligands.     

Molecular structures and supramolecular association of chlorodiorganotin(IV) complexes with bis- and tris-dithiocarbamate ligand

Two series of di and trinuclear chlorodiorganotin(IV) complexes derived from bis- and tris-dithiocarbamate ligands have been prepared and structurally characterized. The dinuclear complexes 1-2 of the composition {(R₂SnCl)₂(bis-dtc)} (1, R = Me; 2, R = ⁿBu) have been obtained from R₂SnCl₂ (R = Me, ⁿBu) and the triethylammonium salt of N,N′-dibenzyl-1,2-ethylene-bis(dithiocarbamate). The trinuclear complexes 3-9 with the general formula {(R₂SnCl)₃(tris-dtc)} 3, R = Me, tris-dtc = tris-dtc-Me; 4, R = Me, tris-dtc = tris-dtc-ⁱPr; 5, R = Me, tris-dtc = tris-dtc-Bn; 6, R = ⁿBu, tris-dtc = tris-dtc-Me; 7, R = ⁿBu, tris-dtc = tris-dtc- ⁱPr; 8, R = ⁿBu, tris-dtc = tris-dtc-Bn; 9, R = ^tBu, tris-dtc = tris-dtc-Me) were prepared from R₂SnCl₂ (R = Me, ⁿBu, ^tBu) and the potassium dithiocarbamate salts of (tris[2-(methylamino)ethyl]amine) (tris-dtc-Me), (tris[2-(isopropylamino)ethyl]amine) (=tris-dtc-ⁱPr) and (tris[2-(benzylamino)ethyl]amine) (=tris-dtc-Bn). Compounds 1-9 have been analyzed as far as possible by elemental analysis, FAB⁺ mass spectrometry, IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy, and single-crystal X-ray diffraction analysis. The solid state and solution studies showed that the dtc ligands are coordinated to the tin atoms in the anisobidentate manner. In all cases the metal centers are five-coordinate. The coordination geometry is intermediate between square-pyramidal and trigonal-bipyramidal coordination polyhedra with τ-values in the range of 0.32-0.53. For the members of each series characterized in the solid state by X-ray diffraction analysis, different molecular conformations were found. The crystal structures show the presence of C-H?Cl, C-H?S, C-H?π, S?Cl, S?S, Cl?Sn and S?Sn contacts.     

Synthesis of palladium and platinum donor complexes and study of their participation in self-assembly reactions. X-ray crystal structure of [Pt(C6H4CCC5H4N)2(dppp)] (dppp = 1,3-bis(diphenylphosphino)propane)

Novel square-planar compounds [M(NC₅H₄CCH)₂(dppp)](OTf)₂ (M = Pd (1), Pt (2)), [Pt(CCC₆H₄CN)₂(dppp)] (3) and [Pt(C₆H₄CCC₅H₄N)₂(dppp)] (4) (dppp = 1,3-bis(diphenylphosphino)propane) were prepared and characterised. Their potential as building blocks in the generation of heterobimetallic squares was studied. The reaction of 4 and the ditopic acceptor species [Pd(H₂O)₂(dppf)](OTf)₂ enabled a tetrametallic metallocycle containing two platinum and two palladium atoms to be obtained. The crystal X-ray structure of 4 shows that the Pt?N vectors are nearly perpendicular, and confirm the suitability of the compound to act as a corner unit for the construction of molecular squares.     

Variation in crystalline architectures through supramolecular interactions in copper(II) complexes with tridentate N2O donor Schiff bases

Three copper(II) complexes, [Cu(L¹)(H₂O)(ClO₄)]·0.5H₂O (1), [Cu(L²)(H₂O)(ClO₄)]·0.5H₂O (2), and [Cu(L²)(NCNC(OCH₃)NH₂)]ClO₄ (3), where HL¹ = 4-bromo-2-(-(quinolin-8-ylimino)methyl)phenol and HL² = 1-(-(quinolin-8-ylimino)methyl)naphthalen-2-ol, have been prepared and characterized by elemental analysis, IR, UV–vis and fluorescence spectroscopy and single-crystal X-ray diffraction studies. The copper(II) centers assume five-coordinate square-pyramidal geometries in 1 and 2, whereas square planar copper(II) is present in 3. A methanol molecule has been inserted in the pendant end of the ligated dicyanamide in 3. Various supramolecular architectures are formed by hydrogen bonding, π?π, C–H?π, and lp?π interactions.     

Spectroscopic study of ternary copper(II) complexes on a silica surface

The formation of ternary surface complexes of copper(II) with one or two molecules of 2,2′-bipyridine (bpy) or α-picolinic acid (Hpic), which were obtained after adsorption on the silica surface in different ways, was studied by electronic and ESR spectroscopy. Coordination of the ligands, which were preliminarily adsorbed by copper ions, afforded only 1∶1 ternary surface complexes. In both cases, coordinatively more saturated ternary surface complexes were formed only when Cu(bpy)₂ ²⁺ and Cu(pic)₂ were adsorbed on the SiO₂ surface from solutions. The compositions and structures of the ternary surface complexes containing bipyridine ligands are temperature independent, whereas in the picolinate-containing ternary surface complexes, the coordination spheres of the adsorbed complexes are rearranged as the temperature changes. Presented at the First Moscow Workshop on Highly Organized Catalytic Systems (June 19, 1997). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1765–1771, October, 1997.     

Self-assembly of triorganotin(IV) moieties with 2,3,4,5-tetrafluorobenzoic acid and 4,4′-bipy, triphenylphosphine oxide or phen: Syntheses, characterizations and supramolecular structures

A series of triorganotin (IV) complexes with 2,3,4,5-tetrafluorobenzoic acid and mixed-ligands of the types: R₃Sn(O₂CC₆HF₄)_m · L (m = 1, L = 0, R = Ph 1; m = 1, L = Ph₃PO, R = Ph 4, Me 5), [R₃Sn(O₂CC₆HF₄)]_m · L (m = 2, L = 4,4′-bipy, R = Ph 2, Me 3; m = n, L = 0, R = Me 6), and [R₃Sn(O₂CC₆HF₄) · (H₂O)]_m · L · C₂H₅OH (m = 2, L = Phen, R = Ph 7, Me 8), (4,4′-bipy = 4,4′-bipyridyl; Phen = 1,10-phenanthroline), have been synthesized by the reaction of triorganotin chloride and 2,3,4,5-tetrafluorobenzoic acid in the presence of mixed-ligands: 4,4′-bipy, triphenylphosphine oxide, or phen. All complexes were characterized by elemental analysis, IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy analysis. Except for 5 and 8, all the complexes were also characterized by X-ray crystallography.     

Supramolecular Organometallic Polymer Chemistry: Self-Assembly of a Novel Poly(ferrocene)-b-polysiloxane-b-poly(ferrocene) Triblock Copolymer in Solution

Micelles with unprecedented flowerlike arrangements of the poly(ferrocene) cores (shown in the TEM image) are among the supramolecular architectures generated in the self-assembly of a novel organometallic triblock copolymer from silicon-bridged [1]ferrocenophane monomers and [Me₂SiO]₃ in hexane, a solvent selective for the central polysiloxane block.     

Attempted synthesis of axial-equatorial pyrazine-bridged copper(II) complexes toward homometallic ferromagnetic compounds

The introduction of a relatively bulky alkyl group at 2-position of pyrazine afforded unique μ-pyz complexes, namely, dinuclear [{Cu(hfac)₂}₂(μ-2-isobutylpyrazine)], trinuclear [{Cu(hfac)₂}₃(μ-2-isopropylpyrazine)₂], and polymeric [Cu(hfac)₂(μ-ibupyz)]_n (Hhfac stands for 1,1,1,5,5,5-hexafluoropentane-2,4-dione). These compounds have an axial-equatorial dinuclear moiety, which is expected to show ferromagnetic interaction. However, they exhibited practically negligible or very weak antiferromagnetic interaction. This may be due to violation of orthogonality because of the steric hindrance of the isobutyl or isopropyl groups. We analyzed the relationship between the structural deformation parameter defined as the N(eq)?N(ax)-Cu angle and the exchange coupling parameter. A critical angle, at which the sign of the magnetic coupling changes from positive to negative, is estimated to be 165(2)°. The present results are reasonably explained in this relation.