Towards surface-supported supramolecular architectures: tailored coordination assembly of 1,4-benzenedicarboxylate and Fe on Cu(100)

We present a comprehensive investigation of the modular assembly of surface-supported metal-organic coordination systems with specific topologies and high structural stability formed by vapor deposition of 1,4-benzenedicarboxylic acid molecules and iron atoms on a Cu(100) surface under ultra-high vacuum conditions. By making use of the two carboxylate moieties available for lateral linkage to Fe atoms, we succeeded in the fabrication of distinct Fe-carboxylate coordination architectures at the surface by carefully adjusting the ligand and metal concentration ratio and the temperature of the post-deposition annealing treatment. The mononuclear, 1D-polymeric and fully 2D-reticulated metallosupramolecular arrangements obtained were characterized in situ at the single-molecule level by scanning tunneling microscopy.     

Supramolecular assemblies of a series of 2-arylbenzimidazoles at the air/water interface: in situ coordination, surface architecture and supramolecular chirality

The spreading behavior and supramolecular assemblies of some arylbenzimidazoles with 2-substituted aromatic groups such as phenyl, naphthyl, anthryl and pyrenyl on water surface and the subphase containing AgNO3 were investigated. It was observed that although these compounds lack long alkyl chains, they showed surface activity when spread from chloroform solution on water surface and formed the supramolecular assemblies. When AgNO3 was present in the subphase, a coordination between the imidazole group of the compounds and Ag(I) occurred in situ in the spreading film, which was verified by the surface pressure/area (pi-A) isotherms and UV/Vis absorption spectra. Both the spreading films from water and the aqueous AgNO3 subphase were transferred onto solid substrates and their surface morphologies as well as properties were characterized by AFM, UV/Vis absorption and CD spectra. Various surface morphologies such as nanoparticles, block domains and nanoutensils were observed depending on the substituted aromatic groups. Interestingly, although all of these compounds were achiral, supramolecular chirality was obtained for some of the arylbenzimidazole films assembled from either the water surface or the subphase containing AgNO3. It was revealed that chiral assemblies could be obtained from water surface for the benzimidazoles which have pyrenyl or alpha-naphthyl groups. For benzimidazole derivative with anthryl group, chiral assemblies could be obtained when spreading on the aqueous AgNO3 subphase. For the benzimidazoles with phenyl or beta-naphthyl groups, no chirality was obtained. It was suggested that both the overcrowded stacking of the aromatic groups and the cooperative arrangement of the molecules on water surface or aqueous AgNO3 subphase play a crucial role in forming the chiral supramolecular assemblies.     

Simultaneous end-on/side-on coordination modes of a diphosphorus tetrahedral complex imposed by pre-organization of oligometallic Cu(I) acceptors

The reaction of the [{CpMo(CO)(2)}(2)(μ,η(2):η(2)-P(2))] (Cp=cyclopentadienyl) metallo-ligand 2 with pre-organized Cu(I) bi- and trimetallic precursors afforded new coordination complexes with unprecedented coordination modes for a Mo(2)P(2) complex. Variable-temperature solution and solid-state (31)P NMR spectroscopy measurements were performed and X-ray diffraction studies revealed an η(2):η(1) coordination mode for the Mo(2)P(2) unit of 2 in the Cu(I) bimetallic complexes 3 and 4. DFT calculations were carried out to highlight the bonding situation of this unprecedented coordination mode in the Cu(I) bimetallic compound 3. It is built up from a side-on coordination of the P-P σ bond to one copper ion and from the interaction of the lone pair of one phosphorus atom with the second copper ion. The remaining available lone pair of the second phosphorus atom can be involved as well to interact with an additional metal centre, as evidenced in the Cu(I) trimetallic compound 5 in which an η(2):η(1):η(1) coordination mode of the ligand 2 is observed. Derivative 3 can be used as a molecular clip to obtain discrete π-stacked dimers through a ligand exchange reaction between acetonitrile ligands and cyano-capped π-conjugated systems, indicating the stability of the new η(2):η(1) coordination mode.     

Supramolecular Paradigm for Capture and Co-Precipitation of Gold(III) Coordination Complexes

A new supramolecular paradigm is presented for reliable capture and co-precipitation of haloauric acids (HAuX₄) from organic solvents or water. Two classes of acyclic organic compounds act as complementary receptors (tectons) by forming two sets of directional non-covalent interactions, (a) hydrogen bonding between amide (or amidinium) NH residues and the electronegative X ligands on the AuX₄⁻, and (b) electrostatic stacking of the electron deficient Au center against the face of an aromatic surface. X-ray diffraction analysis of four co-crystal structures reveals the additional common feature of proton bridged carbonyls as a new and predictable supramolecular design element that creates one-dimensional polymers linked by very short hydrogen bonds (CO⋅⋅⋅OC distance <2.5 Å). Two other co-crystal structures show that the amidinium-π⋅⋅⋅XAu interaction will reliably engage AuX₄⁻ with high directionality. These acyclic compounds are very attractive as co-precipitation agents within new “green” gold recovery processes. They also have high potential as tectons for controlled self-assembly or co-crystal engineering of haloaurate composites. More generally, the supramolecular paradigm will facilitate the design of next-generation receptors or tectons with high affinity for precious metal square planar coordination complexes for use in advanced materials, nanotechnology, or medicine.     

Guest-dependent flexible coordination networks with fluorinated ligands

Guest-dependent flexible coordination networks are formed from 1,4-bis(4-pyridylmethyl)tetrafluorobenzene (bpf), 4,4'-bis(4-pyridylmethyl)octafluorobiphenyl (bpfb), 2,6-bis(4-pyridylmethyl)hexafluoronaphthalene (2,6-bpfn), and 2,7-bis(4-pyridylmethyl)hexafluoronaphthalene (2,7-bpfn) with Cd(NO3)2 in the presence of various organic compounds. The reaction of bpf affords one-dimensional cyclic chains, two-dimensional rhombus grid sheets, and three-dimensional diamond frameworks with threefold interpenetration. The reaction of bpfb mainly affords two-dimensional rhombus grid sheets with twofold parallel interpenetration. The reaction of 2,6-bpfn affords a one-dimensional ladder and two-dimensional rhombus grid, twisted grid, and herringbone sheets. The reaction of 2,7-bpfn affords two-dimensional rhombus grid sheets and grid sheets with dumbbell-shaped cavities. This diversity of network topologies is induced by interactions between the guest molecules and the flexible ligand frameworks.     

Spontaneous formation of heteroligated PtII complexes with chelating hemilabile ligands

The spontaneous formation of the heteroligated complex [PtCl(kappa(2)-Ph(2)PCH(2)CH(2)SMe)(Ph(2)PCH(2)CH(2)SPh)]Cl (8 a) by a novel ligand rearrangement process has been observed. By using the weak-link approach, the relative arrangement of the alkyl and aryl groups can be controlled by abstraction of chloride from 8 a to form the closed complex [Pt(kappa(2)-Ph(2)PCH(2)CH(2)SMe)(kappa(2)-Ph(2)PCH(2)CH(2)SPh)][BF(4)](2) (5) and reopening using halide ions to form semi-open complexes [PtX(kappa(2)-Ph(2)PCH(2)CH(2)SMe)(Ph(2)PCH(2)CH(2)SPh)]BF(4) (8 b; X=Cl(-)) and (8 c; X=I(-)). Analogous procedures using Ph(2)PCH(2)CH(2)SMe and 1,4-(Ph(2)PCH(2)CH(2)S)(2)C(6)H(4) lead to heteroligated bimetallic complexes 7 and 9, illustrating that this ligand rearrangement process can be used as a tool for the assembly of complementary metallosupramolecular structures.     

Redox-induced coordination isomerization of a phosphoniobenzophospholide

1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a,b were characterized by X-ray diffraction studies as well. The structural and (31)P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the eta(2)-bound Pdbond;C double bond moieties is dominated by the L-->M charge-transfer contribution; this hints at a very low back-donation ability of the central M(2)(CO)(6) fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF(6)]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF(6)] gave spectroscopic evidence for the formation of a Re analogue of 6 a. Electrochemical studies suggested that the oxidation 8 a-->2 6 a involves two consecutive single-electron-transfer steps, the first of which is electrochemically reversible and produces a metastable radical cation that is detectable by ESR spectroscopy. The mutual interconversion between 6 a and 8 a represents the first case of a reversible coordination isomerization of a phosphaarene that is triggered by a redox process and might stimulate further studies directed at the use of dinuclear phosphaarene complexes in redox-catalysis.     

Decacyclene as complexation manifold: synthesis, structure and properties of its Fe2 and Fe4 slipped triple-decker complexes

Reaction of [(eta(5)-Me4EtC5)Fe(II)Cl(tmeda)] (tmeda = N,N,N'N'-tetramethylethylenediamine) with a polyanion solution of decacyclene (1) results in the formation of the triple-deckers [{(eta(5)-Me4EtC5)Fe}2-mu2-(eta(6):eta(6)-decacyclene)] (3) and [{(eta(5)-Me4EtC5)Fe}4-mu4-(eta(6):eta(6):eta(6):eta(6)-decacyclene)] (4). Metal complexation in 3 and 4 occurs on opposite faces of the pi perimeter in an alternating mode. The decacyclene ring adopts a gently twisted molecular propeller geometry with twofold crystallographic symmetry (C2). Complex 4 crystallizes in the chiral space group C222(1); the investigated crystal only contains decacyclene rings with M chirality. The handedness can be assigned unambiguously to the presence of the iron atoms. Cyclovoltammetric studies revealed quasireversible behavior of the redox events and a strong interaction of the Fe atoms in 3 and 4, exemplified by potential differences deltaE of 660 and 770(780) mV between the first and the second individual oxidation processes. This corresponds to a high degree of metal-metal interaction for 3 and 4. The successful syntheses of 3 and 4 together with earlier results from our laboratory proves that all five- and six-membered pi subunit sets of 1 are prone to metal complexation. A clear site preference in 1 towards the complexation of [Cp(R)]iron, -cobalt, and -nickel fragments exists.     

Supramolecular coordination chemistry: the synergistic effect of serendipity and rational design

Supramolecular coordination compounds bear exceptional advantages over their organic counterparts. They are available in one-pot reactions and in high yields and display physical properties that are generally inaccessible with organic species. Moreover, their weak, reversible, noncovalent bonding interactions facilitate error checking and self-correction. This Review emphasizes the achievements in supramolecular coordination chemistry initiated by serendipity and their materialization based on rational design. The recognition of similarities in the synthesis of different supramolecular assemblies allows prediction of potential results in related cases. Supramolecular synthesis obeys guidelines comparable to the "lead sheet" used by small jazz ensembles for improvisation and therefore more often leads to unpredicted results. The combination of detailed symmetry considerations with the basic rules of coordination chemistry has only recently allowed for the design of rational strategies for the construction of a variety of nanosized systems with specified size and shape.