Biing-Chiau Tzeng

Anion-recognition studies of a Re(I)-based square containing the dipyridyl-amide ligand

The molecular square [Re(CO)3Cl(L)]4 (1) containing the dipyridyl-amide ligand, N,N′-4-dipyridyloxalamide (L), was constructed from Re(CO)5Cl and L for the purpose of anion-recognition studies. Upon addition of fluoride anions to a THF solution of 1, a remarkable spectral change is observed, and indeed a new absorption band grows at ca. 348 nm. We reasoned that upon addition of fluoride, the hydrogen bonds between F− and –NH groups of L would first form and increase the electron densities of nitrogen atoms. This in turn increases the conjugation throughout the L ligand, which is responsible for the new growing absorption band. Finally, a proton-transfer process occurs upon addition of excess F− anions, corroborated by the 1H NMR titration experiment due to the occurrence of HF2−. The binding constants based on a 1 ∶ 1 complex (1–X−, X− = anions) follow the order: F− > CN− > OAc− > Cl− > Br−, PF6−, BF4−, ClO4−, NO3− and HSO4−. The most electronegative F− anion shows the largest binding constant, followed by CN−, OAc− and Cl− anions. The less electronegative Br− anion and bigger PF6−, BF4−, ClO4−, NO3− and HSO4− anions do not show any binding affinity with 1. The control titrations carried out using L and the same series of anions showed that the basicity of anions also possibly lends some contribution to the sensing events. However, the binding affinity of 1 toward various anions can be mostly correlated with the electronegativity as well as cavity size of the molecular square, and hence 1 can be expected to be a sensor for F−.

Photophysical properties, crystal structure, and host–guest interaction of a luminescent tetranuclear gold(I)-phenylacetylide complex with a supramolecular phosphine ligand

A novel tetranuclear gold(I)-phenylacetylide complex containing a tetraazamacrocycle cavity is prepared by the reaction of [Au(CCPh)]∞ with the ligand 1,4,8,11-tetra(diphenylphosphinomethyl)- 1,4,8,11-tetraazacyclotetradecane and its structure characterized by X-ray crystal analysis; this complex shows dramatic changes in absorption and emission properties upon complexation with alkali- and transition-metal ions.

Self-assembly of N,N′,N″-tris(4-pyridyl)trimesic amide and N,N′,N″-tris(3-pyridyl)trimesic amide with AgI or CdII ions

We report herein an interesting family of tripyridyltriamides (L1 ≡ N,N′,N″-tris(3-pyridyl)trimesic amide, L2 ≡ N,N′,N″-tris(4-pyridyl)trimesic amide) used as tridentate bridging ligands to carry out crystal-engineering studies. The reaction of AgPF6 with L1 leads to a 2-D coordination polymer, [Ag(L1)PF6]n (1). The 48-membered macrocycles constructed from three-coordinate AgI ions as connectors and three tripyridyltriamide moieties propagate into 2-D extended structures. Indeed, the AgI⋯π interaction (the distance of the AgI⋯centroid of benzene is 3.209 A) increases the supramolecular complexity, and leads to inter-sheet dimerization. The reaction of CdCl2 with L2 forms a 3-D coordination network, [Cd(L2)2Cl2]n (2). The open channels with a diameter of ca. 7.5 A containing the tripyridyltriamide moieties propagate into 3-D extended structures. This is an interesting example of 3-D coordination networks containing tripyridyltriamides as functional moieties inside the channels. However, the channels are filled with disordered water molecules and chloride anions, where the latter are appended through hydrogen-bonding interactions with the amide moieties inside the channels. In addition, 1 displays a high-energy emission with a maximum at ca. 450 nm, whereas 2 shows a low-energy emission with a maximum at ca. 532 nm. The former with a ca. 450 nm emission is assigned to an intraligand transition, and the latter with a ca. 532 nm emission is tentatively ascribed to a metal-to-ligand charge-transfer transition.

Anion-directed assembly of supramolecular zinc(II) halides with N,N′-bis-4-methyl-pyridyl oxalamide

We report here the supramolecular structures and solid state luminescence of zinc(II) halides with N,N′-bis-4-methyl-pyridyl oxalamide (L), where the supramolecular assembly formed is dependent on the halide, and led to the formation of one-dimensional coordination polymers for Cl ([ZnCl2(L)]n) and Br ([ZnBr2(L)]n) or a discrete macrocycle for I ([ZnI2(L)]2), respectively. The rectangular structure of iodo compounds with pyridyl amide L shows an interesting nanotube framework built from π⋯π interactions in combination with hydrogen bonding. To our knowledge, these are rare examples of the anion-directed assembly of supramolecular structures. The low energy emission at ca. 500 nm for [ZnI2(L)]2 is assigned to a ligand-to-metal charge-transfer (LMCT) transition.

Photoluminescent properties and molecular structure of [{Au(PPh3)}2(µ-bbzim)] and[{Au(PPh3)}4(µ-bbzim)][ClO4]2(bbziM = 2,2′-bibenzimidazolate)

The tetranuclear [{Au(PPh3)}4(µ-bbzim)][ClO4]2 and dinuclear [{Au(PPh3)}2(µ-bbzim)] complexes with 2,2′-bibenzimidazolate (bbzim) as bridging ligand have been characterized by X-ray crystallography. The intramolecular Au–Au separations in [{Au(PPh3)}4(µ-bbzim)][ClO4]2 are 3.157(1)–3.222(1)A. Upon excitation at 330 nm, both complexes display intense intraligand fluorescence and phosphorescence in fluid solution at room temperature.

A novel trinuclear Re(I) complex containing 1,3,4-thiadiazole-2,5-dithiolate: structural and spectroscopic properties

In the title complex [SSS(Re(CO)5)3](CF3SO3) (SSS = 1,3,4-thiadiazole-2,5-dithiolate), SSS adopts a two-S/one-N (κ3) coordination form, representing an unprecedented coordination pattern for this ligand. In addition, its solid-state structure confirms that an interesting anion π-interaction (2.880 A) between the N-heterocyclic ligand and the CF3SO3− anion is observed.

Single-crystal-to-single-crystal transformation and solvochromic luminescence of a dinuclear gold(I)-(aza-[18]crown-6)dithiocarbamate compound.

The treatment of [AuCl(SMe2 )] with an equimolar amount of NaO5 NCS2 (O5 NCS2 =(aza-[18]crown-6)dithiocarbamate) in CH3 CN gave [Au2 (O5 NCS2 )2 ]⋅2 CH3 CN (2⋅2 CH3 CN), and its crystal structure displays a dinuclear gold(I)-azacrown ether ring and an intermolecular gold(I)⋅⋅⋅gold(I) contact of 2.8355(3) Å in crystal lattices. It is noted that two other single crystals of 2⋅tert-butylbenzene⋅H2 O and 2⋅0.5 m-xylene can be successfully obtained from a single-crystal-to-single-crystal (SCSC) transformation process by immersing single crystals of 2⋅2 CH3 CN in the respective solvents, and both also show intermolecular gold(I)⋅⋅⋅gold(I) contacts of 2.9420(5) and 2.890(2)-2.902(2) Å, respectively. Significantly, the emissions of all three 2⋅solvates are well correlated with their respective intermolecular gold(I)⋅⋅⋅gold(I) contacts, where such contacts increase with 2⋅2 CH3 CN (2.8355(3) Å)<2⋅0.5 m-xylene (2.890(2)-2.902(2) Å)<2⋅tert-butylbenzene⋅H2 O (2.9420(5) Å), and their emission energies increase with 2⋅2 CH3 CN (602 nm)<2⋅0.5 m-xylene (583 nm)<2⋅tert-butylbenzene⋅H2 O (546 nm) as well. In this regard, we further examine the solvochromic luminescence for some other aromatics, and finally their emissions are within 546-602 nm. Obviously, the above results are mostly ascribed to the occurrence of intermolecular gold(I)⋅⋅⋅gold(I) contacts in 2⋅solvates, which are induced by the presence of various solvates in the solid state, as a key role to be responsible for their solvochromic luminescence.

Dramatic solvent effect on the luminescence of a dinuclear gold(i)complex of quinoline-8-thiolate

The complex [{Au(PPh 3 )} 2 (8-qnS)]BF 4 (8-qnS = quinoline-8-thiolate) with intramolecular gold(I)...gold(I) distances of 2.991(2) and 3.081(2) A in two independent asymmetric units, shows a long-lived emission at 640 nm which is quenched by polar solvents such as acetonitrile and alcohol.

Luminescent gold(i) supermolecules with trithiocyanuric acid.Crystal structure, spectroscopic and photophysical properties

The first example of an ordered array of Au 6 clusters with trithiocyanuric acid, [(LAu)(AuPPhMe 2 ) 2 ] 2 (H 3 L = trithiocyanuric acid), is prepared and characterized by X-ray crystallography; it has a two-dimensional structure via intermolecular Au I ···Au I interactions and possesses photoluminescence properties; the ability of trithiocyanuric acid to act as a bridging ligand for molecular assembly of two-dimensional polymeric solids is demonstrated.

Toward heteronuclear supramolecular architectures of pyridine-4-thiolate

The reaction of Pt(d-t-bpy)(S-4-py)2 (1; d-t-bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, S-4-py = pyridine-4-thiolate) with ZnX2 (X = Cl, Br, I) gave the respective heteronuclear metallocycles, [Pt(d-t-bpy)(S-4-py)2(ZnX2)]2 (X = Cl 2, Br 3, and I 4). In particular, the presence of weak intermolecular Pt(II)⋯Pt(II) (3.374 and 3.453 A for 2; 3.364 and 3.452 A for 3) and π⋯π (3.279 and 3.490 A for 2; 3.574 and 3.793 A for 3) interactions makes the heteronuclear metallocycles cooperatively stack to form a monohelical chain, and four monohelices are further stacked to give a novel bundle-of-quadruple-monohelix through nonclassical hydrogen bonding. However, 4 having only π⋯π interactions, possibly due to the larger atom size for I, cannot form a similar structural framework as those of 2 and 3. Hence, the presence of weak Pt(II)⋯Pt(II) interactions seems to play a vital role for the formation of such a novel structural motif. For the NO3 complex, [Pt2(d-t-bpy)2(S-4-py)4(Zn(NO3))2(μ-O)]n (5), a one-dimensional ladder structure is formed instead of a heteronuclear metallocycle. Therefore, a delicate anion-induced assembly has been demonstrated. In addition, the emissions of 2–5 are quite similar to that of Pt(d-t-bpy)(S-4-py)2, which has been assigned to a ligand-to-ligand charge-transfer (LLCT) transition, indicating that the coordination to Zn(II) ions through pyridyl-4-thiolate ligands of Pt(d-t-bpy)(S-4-py)2 cannot cause a significant effect on their LLCT emissions.