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A series of blue-green emitting RuII diisocyano complexes containing 2-benzoxazol-2-ylphenolate (PBO) have been prepared. The complexes were isolated under varied reaction conditions in two isomeric forms, i.e., trans,trans,trans- (1) and cis,trans,cis- (2), with varied ligand coordination geometry above the RuII center. The photoluminescence of the isomeric complexes has been compared and tuned by the systematic variation of the electronic properties of the isocyanides. The cis,trans,cis- isomers exhibit structureless emission in the blue-green region (471-517 nm) upon excitation at λex > 400 nm in dichloromethane solution at room temperature. Both isomeric forms show similarly structured greenish emission at 499-523 nm on excitation at λex > 355 nm in a methanol/ethanol (4:1) glassy medium at 77 K. On careful comparison with the corresponding absorption and electrochemical data, it is suggested that the solution emission of the cis,trans,cis- isomers (2) at room temperature is originated from the metal-to-ligand charge transfer (MLCT), while a ligand-centered (LC) parentage is assigned for the emission in a glassy state for both isomeric forms. In line with the above experimental results, DFT calculation demonstrates the change in the nature and relative energy of the HOMOs and LUMOs with respect to the varied ligand coordination geometry and π-accepting ability of the isocyanides.

We have recently reported a strongly luminescent osmium(VI) nitrido complex [OsVI(N)(NO2-L)(CN)3]− [HNO2-L = 2-(2-hydroxy-5-nitrophenyl)benzoxazole]. The excited state of this complex readily activ...

The guanidine moiety of arginine is involved in the active sites of a variety of enzymes, such as nitric oxide synthase (NOS) and NiFe hydrogenase. In this paper we aim to investigate the effects of a metal center on the oxidation of guanidine, which should provide an interesting comparison with the biological aerobic oxidation of arginine catalyzed by NOS. We studied the oxidation of an osmium(III) guanidine complex, mer-[Os(L){N(H)C(NH2)2}(CN)3]−, (OsG, HL = 2-(2-hydroxyphenyl)benzoxazole) by m-chloroperbenzoic acid (m-CPBA), which is potentially an O atom transfer reagent, and by (NH4)2[CeIV(NO3)6], which is a one-electron oxidant. With m-CPBA, mer-[Os(NO)(L)(CN)3]− (mer-OsNO) is the product, while with CeIV, mer-[OsVI(N)(L)(CN)3]− (mer-OsN) is formed instead. The crystal structures of mer-OsNO and mer-OsN were determined by X-ray crystallography. The mechanisms for the oxidation of OsG by m-CPBA and CeIV are proposed.

The aerobic oxidation of the N-hydroxyguanidinum moiety of N-hydroxyarginine to NO is a key step in the biosynthesis of NO by the enzyme nitric oxide synthase (NOS). So far, there is no chemical system that can efficiently carry out similar aerobic oxidation to give NO. We report here the synthesis and X-ray crystal structure of an osmium(III) N-hydroxyguanidine complex, mer-[Os(III){NH═C(NH2)(NHOH)}(L)(CN)3](-) (OsGOH, HL = 2-(2-hydroxyphenyl)benzoxazole), which to the best of our knowledge is the first example of a transition metal N-hydroxyguanidine complex. More significantly, this complex readily undergoes aerobic oxidation at ambient conditions to generate NO. The oxidation is pH-dependent; at pH 6.8, fac-[Os(NO)(L)(CN)3](-) is formed in which the NO produced is bound to the osmium center. On the other hand, at pH 12, aerobic oxidation of OsGOH results in the formation of the ureato complex [Os(III)(NHCONH2)(L)(CN)3](2-) and free NO. Mechanisms for this aerobic oxidation at different pH values are proposed.

A series of homoleptic mononuclear 8-coordinate FeII and CoII compounds, [FeII(L2)2](ClO4)2 (2), [FeII(L3)2](ClO4)2 (3), [FeII(L4)2](ClO4)2 (4), [CoII(L1)2](ClO4)2 (5), [CoII(L2)2](ClO4)2 (6), [CoII(L3)2](ClO4)2 (7), and [CoII(L4)2](ClO4)2 (8) (L1 and L2 are 2,9-dialkylcarboxylate-1,10-phenanthroline ligands; L3 and L4 are 6,6′-dialkylcarboxylate-2,2′-bipyridine ligands), have been obtained, and their crystal structures have been determined by X-ray crystallography. The metal center in all of these compounds has an oversaturated coordination number of 8, which is completed by two neutral homoleptic tetradentate ligands and is unconventional in 3d-metal compounds. These compounds are further characterized by electronic spectroscopy, cyclic voltammetry (CV), and magnetic measurements. CV measurements of these complexes in MeCN solution exhibit rich redox properties. Magnetic measurements on these compounds demonstrate that the observed single-ion magnetic (SIM) behavior in the previously reported [FeII(L1)2...

One-dimensional (1D) homochiral nickel coordination polymers [Ni(3)(bpdc)(RR-L)(2)·(DMF)](n) (2R, RR-L = (R,R)-(-)-1,2-cyclohexanediamino-N,N'-bis(3-tert-butyl-5-(4-pyridyl)salicylidene), bpdc = 4,4'-biphenyldicarboxylic acid) and [Ni(3)(bpdc)(SS-L)(2)·(DMF)](n) (2S, SS-L = (S,S)-(-)-1,2-cyclohexanediamino-N,N'-bis(3-tert-butyl-5-(4-pyridyl)salicylidene) based on enantiopure pyridyl-functionalized salen(Ni) metalloligand units NiL ((1,2-cyclohexanediamino-N,N'-bis(3-tert-butyl-5-(4-pyridyl)salicylidene))Ni(II)) have been synthesized and characterized by microanalysis, IR spectroscopy, solid-state UV-vis spectroscopy, thermogravimetric analysis (TGA), circular dichroism (CD) spectroscopy, cyclic voltammetric measurement, and powder and single crystal X-ray diffraction. Each NiL as unbridging pendant metalloligand uses one terminal pyridyl group to coordinate achiral unit (nickel and bpdc(2-)) building a helical chain, while the other pyridyl group remains uncoordinated. Both 2R and 2S contain left- and right-handed helical chains made of the achiral building blocks, while the NiL as remote external chiral source is perpendicular to the backbone of the helices. The nickel coordination polymers 2R and 2S containing unsaturated active nickel center in metalloligand NiL can be used as self-supported heterogeneous catalysts. They show catalytic activity comparable with their homogeneous counterpart in alkene epoxidation and exhibit great potential as recyclable catalysts.

Reaction of [Ru (VI)(N)(L (1))(MeOH)] (+) (L (1) = N, N'-bis(salicylidene)- o-cyclohexylenediamine dianion) with excess pyridine in CH 3CN produces [Ru (III)(L (1))(py) 2] (+) and N 2. The proposed mechanism involves initial equilibrium formation of [Ru (VI)(N)(L (1))(py)] (+), which undergoes rapid N...N coupling to produce [(py)(L (1))Ru (III) N N-Ru (III)(L (1))(py)] (2+); this is followed by pyridine substituion to give the final product. This ligand-induced N...N coupling of Ru (VI)N is utilized in the preparation of a series of new ruthenium(III) salen complexes, [Ru (III)(L)(X) 2] (+/-) (L = salen ligand; X = H 2O, 1-MeIm, py, Me 2SO, PhNH 2, ( t )BuNH 2, Cl (-) or CN (-)). The structures of [Ru (III)(L (1))(NH 2Ph) 2](PF 6) ( 6), K[Ru (III)(L (1))(CN) 2] ( 9), [Ru (III)(L (2))(NCCH 3) 2][Au (I)(CN) 2] ( 11) (L (2) = N, N'-bis(salicylidene)- o-phenylenediamine dianion) and [N ( n )Bu 4][Ru (III)(L (3))Cl 2] ( 12) (L (3) = N, N'-bis(salicylidene)ethylenediamine dianion) have been determined by X-ray crystallography.

Monodispersed silver nanoparticles (Ag(0) NPs) have been first prepared on the basis of a postsynthesis via mild reduction from a new crystalline supramolecular hybrid solid assembled from Ag(+) ions and decamethylcucurbit[5]uril (Me10CB[5]). Uniform growth of nearly spherical Ag(0) NPs with an average size of ca. 4.4 nm was observed on the organic Me10CB[5] support to form Ag@Me10CB[5] composite material. The as-synthesized composite material was characterized by a range of physical measurements (PXRD, TGA, XPS, ICP, TEM, etc.) and was further exploited as a heterogeneous catalyst for the reduction of various nitrophenols in the presence of NaBH4. The kinetics of the reduction process was monitored under various experimental conditions. The Ag@Me10CB[5] composite material showed excellent catalytic performance over the reduction reactions and remained active after several consecutive cycles.

Four cubane-like Cu4I4 units are assembled around an iodine atom to form the giant, mixed-valent Cu(II)Cu(I)15I17 cluster. The Cu(II)Cu(I)15I17 cluster and a bipyrazole linker form a 3D open framework with paramagnetic and thermochromic properties. This paper also touches on the resemblance of this cluster to the self-similar object of a Sierpinski tetrahedron.

A series of silver complexes of polyoxometalates (POMs), formulated as, [Ag(2)(4,4'-bpy)(2)(4,4'-Hbpy)(H(2)O)][PW(12)O(40)] (4,4'-bpy = 4,4'-bipyridine, 1), [Ag(4)(4,4'-bpy)(4)][4,4'-H(2)bpy][P(2)W(18)O(62)].4H(2)O (2), [Ag(4)(4,4'-bpy)(4)][H(2)P(2)W(18)O(62)].7H(2)O (3), and Na(8)[Ag(3)(4,4'-bpy)(3)][PW(10)Ag(2)O(39)].6H(2)O (4), have been hydrothermally synthesized in situ at different pH. Complex 1, based on saturated Keggin POM building blocks and silver coordination compounds, exhibits an interesting 3-fold interpenetration of diamondlike network in the POM chemistry. Different from complex 1, complexes 2-3 consist of Wells-Dawson polyoxoanions and silver coordination compounds. Complex 2 represents the highest coordination number of Wells-Dawson polyoxoanions, which helps to form a high-dimensional framework with (4.6(4).8)(4)(4(4).6(16).8(8)) topology. Thee-dimensional (3D) Wells-Dawson phosphotungstate 3 reveals another new topology (4.6(4).7)(4.6(4).8)(2)(4(3).6(8).7(2).8(2)). Complex 4 forms a 3D framework constructed from divacant Keggin polyoxoanions and silver coordination compounds. Their structural differences indicate that the pH value of the reaction system plays a key role on the structures and topologies of these complexes, and the whole self-assembly process is pH-dependent.

The treatment of [Ru(VI)(N)(L)(MeOH)]PF(6) (1) (L = N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion) with 2 equiv of RNC (R = (a) (t)Bu, (b) Cy) in CH(2)Cl(2) affords a mixture of blue cis-beta-[Ru(III)(NCNR)(L)(CNR)] (2) and green trans-[Ru(III)(L)(CNR)(2)]PF(6) (3) products. The reduction of 3 with a stoichiometric amount of Cp(2)Co in CH(3)CN gives red trans-[Ru(II)(L)(CNR)(2)] (4). Refluxing 4 with 3 equiv of RNC in methanol in the presence of 5 equiv of NH(4)PF(6) affords a yellow complex, mer-[Ru(II)(eta(3)-HL)(CNR)(3)](PF(6)) (5), in which the ligand is in an eta(3)-coordination mode. These complexes are characterized by IR, UV-vis, ESI-MS, CV, magnetic measurements, and CHN elemental analysis. The structures of 2a, 3a, 4a, 4b, and 5a have been determined by X-ray crystallography.