Molecular gold strings: aurophilicity, luminescence and structure-property correlations

This review covers the compound class of one-dimensional gold strings. These compounds feature a formally infinite repetition of gold complexes as monomers/repeating units that are held together by aurophilic interactions, i.e. direct gold-gold contacts. Their molecular structures are primarily determined in the solid state using single crystal X-ray diffraction. The chemical composition of the employed gold complexes is diverse and furthermore plays a key role in terms of structure characteristics and the resulting properties. One of the most common features of gold strings is their photoluminescence upon UV excitation. The emission energy is often dependent on the distance of adjacent gold ions and the electronic structure of the whole string. In terms of gold strings, these parameters can be fine-tuned by external stimuli such as solvent, pH value, pressure or mechanical stress. This leads to direct structure-property correlations, not only with regard to the photophysical properties, but also electric conductivity for potential application in nanoelectronics. Concerning these correlations, gold strings, consisting of self-assembled individual complexes as building blocks, are the ideal compound class to look at, as perturbations by an inhomogeneity in the ligand sphere (such as the end of a molecule) can be neglected. Therefore, the aim of this review is to shed light on the past achievements and current developments in this area.

Synthesis and crystal structure of a cyanido-bridged copper(II)–silver(I) bimetallic complex containing a trimeric {[Ag(CN)2]−}3 anion, [Cu(Dach)2-Ag(CN)2-Cu(Dach)2][Ag(CN)2]3 (Dach=cis-1,2-diaminocyclohexane)

A new cyanido-bridged bimetallic copper(II)–silver(I) complex, [Cu(Dach)2-Ag(CN)2-Cu(Dach)2][Ag(CN)2]3 (1) (Dach=cis-1,2-diaminocyclohexane), has been prepared and characterized by IR spectroscopy and single crystal X-ray analysis. The crystal structure of complex 1 consists of a centrosymmetric trinuclear cation and three non-coordinated [Ag(CN)2]− ions assembled in the form of a trimer, {[Ag(CN)2]−}3. The complex ion is made up of two [Cu(Dach)2]2+ units connected by a bridging [Ag(CN)2]− anion. The copper atom in the complex ion assumes a distorted square pyramidal geometry with CN− nitrogen atoms occupying the apical position. The trinuclear units are joined by hydrogen bonding to form irregular chains.

Hexa-kis-(μ3-2-hy-droxy-naphthalene-1-carboxaldehyde thio-semicarbazonato-κ(3) N (2):S:S)hexa-silver(I) N,N-dimethyl-formamide tetra-solvate

In the title compound, [Ag6(C12H10N3OS)6]·4C3H7NO, the hexa-nuclear complex mol-ecule lies about an inversion center. The six Ag atoms form a distorted octa-hedron, with Ag⋯Ag distances in the range 2.933 (1)-3.401 (1) Å. Each Ag atom is surrounded by one N atom and two thiol-ate S atoms from two deprotonated 2-hy-droxy-1-naphthaldehyde thio-semi-carb-a-zone ligands. Each ligand coordinates three Ag atoms via a bridging thiol-ate S atom and a monodentate N atom, thus two Ag3S3 hexa-gonal rings are linked together. Two dimethyl-formamide solvent mol-ecules are located in four sets of sites with half-occupancy and form O⋯H-N hydrogen bonds to the complex mol-ecule. Intra-molecular O-H⋯N hydrogen bonds are also present. The discrete hexa-nuclear clusters are further linked through π-π inter-actions into layers parallel to (001), the shortest distance between the centroids of aromatic rings being 3.698 (2) Å.

Construction of a dinuclear silver(I) coordination complex with a Schiff base containing 4-amino-1,2,4-triazole ligands

The new ligand 1-(1,2,4-triazol-4-ylimino-meth-yl)-2-naphthol (L) and the title silver(I) complex, namely bis-[μ-1-(1,2,4-triazol-4-ylimino-meth-yl)-2-naphthol]bis-{[1-(1,2,4-triazol-4-yl-imino-meth-yl)-2-naphthol]silver(I)} dinitrate monohydrate, [Ag(2)(C(13)H(10)N(4)O)(4)](NO(3))(2)·H(2)O, were synthesized. Each silver center in the dimeric complex (related by an inversion centre) is coordinated by two bridging L ligands and one additional L ligand in a monodentate fashion, exhibiting a distorted trigonal-planar coordination. The discrete dimers are further linked through O-H⋯O hydrogen bonds and weak π-π stacking inter-actions [the shortest atom-atom separation is ca 3.46 Å between the parallel stacking pairs]. Intramolecular O-H⋯N hydrogen bonds are also present.

Synthesis, Crystal Structure, and Characterization of New Tetranuclear Ag(I) Complexes with Triazole Bridges

The self-assembly of Ag(I) ions with 3,5-dimethyl-4-amino-1,2,4-triazole (L1) and 4-salicylideneamino-1,2,4-triazole (L2) gave two novel complexes, [Ag4(mu2-L1)6][Ag4(mu2-L1)6(CH3CN)2](ClO4)8.2H2O (1) and [Ag4(mu2-L2)6(CH3CN)2](AsF6)4.2H2O (2), both of which contain tetranuclearic clusters constructed via Ag(I) ions and six N1,N2-bridged triazoles with a Ag4N12 core. When 4-(6-amino-2-pyridyl)-1,2,4-triazole (L3) was employed, {[Ag4(mu2-L3)4(mu3-L3)2](CF3SO3)4.H2O}n (3), {[Ag4(mu2-L3)4(mu3-L3)2](ClO4)4}n (4), and {[Ag4(mu2-L3)2(mu3-L3)4](PF6)4.CH3CN.0.75H2O}n (5) were isolated. 3 and 4 are 1D polymers, while 5 is a 2D polymer. 1D and 2D coordination polymers are constructed via the self-assembly of Ag4N12 cores as secondary building units (SBUs). The connection of these SBUs can be represented as a ladderlike structure for 1D polymers and a 4.8(2) net for 2D polymers. Electrospray ionization mass spectrometry measurements and NMR (1H and 13C) studies demonstrate that the tetranuclear SBU retains its integrity and the coordination polymers decompose into the tetranuclear Ag4N12 core in solution. 2 exhibits blue emission in the solid state and green emission in solution at ambient temperature. Strong blue fluorescence for complexes 3-5 in the solid state can be assigned to the intraligand fluorescent emission.

Alkoxo-bridged copper(ii) complexes as nodes in designing solid-state architectures. The interplay of coordinative and d10–d10metal–metal interactions in sustaining supramolecular solid-state architectures

Four novel polymeric coordination networks have been obtained through self-assembly processes involving alkoxo-bridged copperII species as nodes, and anionic cyano-complexes as linkers: infinity2[{Cu2(pa)2}{M(CN)2}2](M=Ag, 1; Au, 2), (infinity)3[{Cu4(mea)4}{Au(CN)2}4.H2O]3, and (infinity)3[{Cu2(pa)2}{Ni(CN)4}](pa = deprotonated propanolamine; mea = deprotonated monoethanolamine). The supramolecular architectures of compounds 1, and 2 are sustained by argentophilic or strong aurophilic interactions. The solid-state architectures of 1 and 2, which are isomorphous, consist of infinite layers, constructed from binuclear alkoxo-bridged nodes and [M(CN)2]- spacers. The layers are stacked in an offset parallel mode, and are further interconnected through Ag...Ag or Au...Au contacts (1: Ag...Ag 3.015 A; 2: Au....Au 3.069 A). Compound 3 consists of unique fourfold interpenetrating diamondoid nets. The diamondoid topology is built of heterocubane {Cu4O4} nodes, which are connected by [Au(CN)2]- rods. The Cu-O distances within the {Cu4O4} node vary between 1.927(2) and 2.679(1) A, showing unsymmetric bridging of the copper atoms. Aurophilic interactions are established between the bridging and terminal [Au(CN)2]- metalloligands, and connect the interpenetrating nets, resulting in infinite chains of gold atoms (the Au...Au distances vary between 3.253 and 3.305 [Angstrom]). Compound 4 exhibits a 3-D network constructed from {Cu2(pa)2]2+ nodes connected by square-planar [Ni(CN)4]2- ions. Compounds 1, 2 and 4 are weakly paramagnetic. The cryomagnetic investigation of reveals a gradual increase, followed by a decrease of the chiMT product, as the temperature is lowered. A superposition of ferro- (J1=+20.8 cm(-1)) and antiferromagnetic (J2=-6.4) interactions within the tetranuclear node was found. Antiferromagnetic interactions are established between the tetranuclear nodes (theta=-2.99 K).