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A series of ESIPT (excited state intramolecular proton transfer) active systems (HQz1-HQz6) derived from quinazoline have been reported. The ESIPT emission for these derivatives gets completely quenched in solvents with diverse polarities which have been restored via aggregation-induced emission (AIE) with large Stokes shift (up to 314 nm). It varied from 450 to 701 nm just by altering substituents at the para position of hydroxy group in the central phenyl ring. As well, HQz1-HQz6 displayed solid state emission [∼455 (blue) to ∼704 nm (red)]. The formyl group on the central hydroxy-phenyl ring of these derivatives induces ESIPT by increasing acidity of the hydroxy proton which has been followed by 1 H NMR studies. Further, it has been clearly shown that emission colour and aggregate morphology can be fine tuned by incorporating apt substituents. The present study offers a simple route to obtain colour tunable ESIPT emission via AIE which is very important for biological imaging and fabrication of optoelectronic devices.

A pioneering approach towards controlling the efficiency of saponification assisted gelation in ethyl ester based ZnII-complexes have been described. Using four new ester containing bis-salen ZnII complexes (C1-C4) involving different para- dye-azo phenyl substituted ligands it has been clearly shown that gelation efficiency is greatly influenced by electronic effect of the substituents (-H, C1; -CH3, C2; -NO2, C3 and -OCH3, C4). Morphological, photophysical, and rheological investigations corroborated well with the experimental observations and established that gelation efficiency enhanced coherently with electron withdrawing characteristics of the substituents (C4 < C2 < C1 < C3) which has also been supported by DFT studies.

Two arrays of “Inorganic-Organic Mixed Gels” (IOMGs) based on terpyridyl complexes have been synthesized combining progelator/non-gelators with easily available, inexpensive and non-reactive small organic non-gelators (SOnGs). This new class of multicomponent gels displays radical changes in morphological patterns and enormous enhancement in their viscoelastic properties relative to weak metallogel (ZTP2G) derived from the progelator only. It has been unequivocally shown that twisting or coiling in gels diminishes as well as their viscoelastic strengths with simple alteration of heteroatoms, their number and positions in SOnGs. Multicomponent gelation is quite complicated considering the susceptibility of anion triggered metallogels towards various external stimuli which has been profoundly outdone. The present approach may be extremely beneficial for negating limitations in the usage of weak metallogels with promising efficacy in specified areas.

One-dimensional nanostructures with aggregation-induced emission (AIE) properties have been fabricated to keep the pace with growing demand from optoelectronics applications. The compounds 2-[4-(4-methylpiperazin-1-yl)benzylidene]malononitrile (PM1), 2-{4-[4-(pyridin-2-yl)piperazin-1-yl]-benzylidene}malononitrile (PM2), and 2-{4-[4-(pyrimidin-2-yl)piperazin-1-yl]benzylidene}malononitrile (PM3) have been designed and synthesized by melding piperazine and dicyanovinylene to investigate AIE in an asymmetric donor-acceptor (D-A) construct of A'-D-π-A- topology. The synthetic route has been simplified by using phenylpiperazine as a weak donor (D), dicyanovinylene as an acceptor (A), and pyridyl/pyrimidyl groups (PM2/PM3) as auxiliary acceptors (A'). It has been established that A' plays a vital role in triggering AIE in these compounds because the same D-A construct led to aggregation-caused quenching upon replacing A' with an electron-donating ethyl group (PM1). Moreover, the effect of restricted intramolecular rotation and twisted intramolecular charge transfer on the mechanism of AIE has also been investigated. Furthermore, it has been clearly shown that the optical disparities of these A'-D-π-A architectures are a direct consequence of comparative A' strength. Single-crystal X-ray analyses provided justification for role of intermolecular interactions in aggregate morphology. Electrochemical and theoretical studies affirmed the effect of the A' strength on the overall properties of the A'-D-π-A system.

Reactions of the complexes [(η 5 -C 5 H 5 )Ru(PPh 3 ) 2 Cl], [{(η 6 -arene)Ru(μ-Cl)Cl} 2 ] (η 6 -arene = C 6 H 6 , C 10 H 14 , and C 6 Me 6 ) and [{(η 5 -C 5 Me 5 )M(μ-Cl)Cl} 2 ] (M = Rh, Ir) with 2-(2-diphenylphosphanylethyl)pyridine (PPh 2 Etpy) were investigated. Neutral κ 1 -P-bonded complexes [(η 5 -C 5 H 5 )Ru(κ 1 -P-PPh 2 EtPy)(PPh 3 )Cl] (1) and [(η 6 -arene)Ru(κ 1 -P-PPh 2 EtPy)Cl 2 ] [arene = C 6 H 6 , (2). C 10 H 14 , (3), and C 6 Me 6 , (4)] were isolated from the reactions of [(η 5 -C 5 H 5 )Ru(PPh 3 ) 2 Cl] and [{(η 6 -arene)-Ru(μ-Cl)Cl} 2 ] with PPh 2 EtPy. Treatment of 1-4 with NH 4 BF 4 / NH 4 PF 6 in methanol allows the synthesis of cationic κ 2 -P,N-chelated complexes [(η 5 -C 5 H 5 )Ru(κ 2 -P,N-PPh 2 EtPy)(PPh 3 )] + (5) and [(η 6 -arene)Ru(κ 2 -P-N-PPh 2 EtPy)Cl] + [arene = C 6 H 6 , (6), C 6 H 14 , (7), and C 6 Me 6 (8)]. On the other hand, the dimers [{(η 5 -C 5 Me 5 )M(μ-Cl)Cl} 2 ] (M = Rh or Ir) reacted with PPh 2 EtPy in methanol to afford cationic κ 2 -P,N-chelated complexes [(η 5 -C 5 Me 5 )M(κ 2 -P-N-PPh 2 EtPy)Cl] + [M = Rh, (9); Ir, (10)]. Complex 10 reacted with an excess amount of sodium azide or sodium chloride to afford the complexes [(η 5 -C 5 Me 5 )-Ir(κ 1 -P-PPh 2 EtPy)X 2 ] (X = N 3 - 11; Cl - , 12), establishing the hemilabile nature of the coordinated PPh 2 EtPy. The complexes were characterized by elemental analyses and various physicochemical techniques. The molecular structures of 1, 5, 6, 9, and 10 were determined crystallographically, and the catalytic potentials of 1-10 were evaluated towards transfer-hydrogenation reactions under aqueous conditions.

Ruthenium complexes [(η 5 -C 5 H 5 )Ru(PPh 3 )(κ 2 -paa)]PF 6 (paa = pyridine-2-carbaldehyde azine) and [(η 5 -C 5 H 5 )Ru(κ 1 -dppm)(κ 2 -paa)]BF 4 [dppm = bis(diphenylphosphanyl)methane] have been employed as a synthon in the synthesis of homo/hetero bi-/trimetallic complexes. It is the uncoordinated N,N-donor site on paa in complex [(η 5 -C 5 H 5 )Ru(PPh 3 )(κ 2 -paa)]PF 6 , and N,N-donor site on paa and pendant phosphorus in [(η 5 -C 5 H 5 )Ru(κ 1 -dppm)(κ 2 -paa)]BF 4 that allows for their incorporation into bi-/trimetallic systems. The resulting complexes have been characterized by analytical, spectral and electrochemical studies. Molecular structures of homo-bimetallic complex [(PPh 3 )(η 5 -C 5 H 5 )Ru(μ-paa)Ru(η 6 -C 10 H 14 )Cl](PF 6 ) 2 and hetero-bimetallic complex [(PPh 3 )(η 5 -C 5 H 5 )Ru(μ-paa)Rh(η 5 -C 5 Me 5 )Cl](PF 6 ) 2 have been authenticated crystallographically. Complexes exhibit absorptions throughout the visible region and complicated electrochemical behaviour. Metal-based Ru II /Ru III oxidations in the bimetallic complexes do not vary as in the trimetallic complexes.

Reactions of the chloro-bridged dimeric complexes [{(η5-C5Me5)M(μ-Cl)Cl}2] (M = Rh, Ir) with the polypyridyl ligands 2,3-di(2-pyridyl)pyrazine (dpp) and 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) in the presence of ammonium tetrafluoroborate gave the mononuclear complexes [(η5-C5Me5)MCl(κ2-dpp)]BF4 [M = Rh (1), Ir (2)] and [(η5-C5Me5)MCl(κ2-tptz)]BF4 [M = Rh (3), Ir (4)]. The complexes have been characterised by elemental analysis, FAB-MS, ESMS, IR, NMR, electronic and emission spectroscopic studies and the molecular structures of 1, 2 and 3 have been crystallographically determined. Structural studies on the complexes revealed the presence of helical superstructures resulting from C–H···X (X = N, F, Cl and π) interactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, structure, reactivity and enzyme inhibitory activity of the new cationic ruthenium complexes [Ru(κ3-L)(EPh3)2Cl]BF4 [L = 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz); E = P (1), As (2)] and their substitution products [Ru(κ3-tptz)(PPh3)(dtc)]Cl (3), [Ru(κ3-tptz)(PPh3)(CN)2] (4), [Ru(κ3-tptz)(AsPh3)(dtc)]BF4 (5), and [Ru(κ3-tptz)(AsPh3)(CN)2] (6) are reported. The complexes were characterized by analytical and spectroscopic methods and the structures of the complexes 1, 2 and 3 determined by X-ray diffraction studies. C−H···X (X = Cl, F and S), C−H···π and π−π interactions were observed in these complexes. Further studies indicated that the complexes [Ru(κ3-L)(EPh3)2Cl]+ could find application as precursors in the synthesis of other ruthenium complexes or as metallo-ligands. The complexes also interact with DNA, which was illustrated by absorption titration studies with CT-DNA and inhibition of topoisomerase II of the filarial parasite Setaria cervi. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Half-sandwich arene ruthenium complexes exhibit versatile chemistry, serve as excellent precursors and find potential applications in many organic transformations. This review mainly focuses on the chemistry of piano-stool ruthenium complexes with special emphasis on the achiral or chiral-at-ruthenium center. Also, it deals with the synthesis, nomenclature and stereochemistry of arene ruthenium complexes along with mechanistic insights into the epimerization reactions and their applications in catalytic organic transformations with some selected examples.

Several known nitrosyl complexes of Ru, Rh, Ir, Co and Mo have been synthesized using a more generalized method, using penicillamine thionitrite as nitrosylating agent. These complexes have been characterised by elemental analyses, spectroscopic (ir, uv, visible and nmr) and magnetic measurements.

Ruthenium complexes [(η5-C5H5)Ru(κ1-P-PPh2Py)(PPh3)Cl] (1) and [(η5-C5H5)Ru(κ2-P-N-PPh2Py)(PPh3)]+ (1a) containing diphenyl-2-pyridylphosphine (PPh2Py) are reported. Coordinated PPh2Py in the complex [(η5-C5H5)Ru(κ1-P-PPh2Py)(PPh3)Cl] (1) exhibits monodentate behavior. In presence of NH4PF6 in methanol at room temperature it afforded chelated complex [(η5-C5H5)Ru(κ2-P,N-PPh2Py)(PPh3)]+ (1a). Further, 1 reacted with various species viz., CH3CN, NaCN, NH4SCN and NaN3 to afford cationic and neutral complexes [(η5-C5H5)Ru(κ1-P-PPh2Py)(PPh3)L]+ and [(η5-C5H5)Ru(κ1-P-PPh2Py)(PPh3)L] [L = CH3CN (1b); CN− (1c); N3− (1d) and SCN− (1e)] and it’s reaction with N,N-donor chelating ligands dimethylglyoxime (H2dmg) and 1,2-phenylenediamine (pda) gave cationic complexes [(η5-C5H5)Ru(κ1-P-PPh2Py)(κ2-N-N)]PF6 [κ2-N-N = dmg (1f) and pda (1g)]. The complexes 1–1g have been characterized by physicochemical techniques and crystal structures of 1, 1a, 1c, 1e and 1f have been determined by single crystal X-ray analyses. Catalytic potential of the complex 1 has been evaluated in water under aerobic conditions. It was observed that the complex 1 selectively catalyzes reduction of aldehyde into alcohol.

Several known nitrosyl complexes of Ru, Rh, Ir, Co, Mo and W have been synthesized using trityl thionitrite as nitrosylating agent at elevated temperatures. Reactions of trityl thionitrite with different salts of Cr, Fe, Co and complexes of Ni, Pd and Pt whose nitrosyls have been obtained only at lower temperatures failed to yield their nitrosyls.

Reactions of nitrosothiourea with different metal ions in the presence of pyridine, 2,2′-bipyridyl, 1,10 phenanthroline and a few complexes of ruthenium, rhodium, iridium, palladium and platinum have been carried out under varying reaction conditions. Physical methods such as IR, magnetic measurements, melting points, mixed melting points and elemental analyses have been used for the identification of reaction products.