Arunabha Thakur

Synthesis of triazole linked fluorescent amino acid and carbohydrate bio-conjugates: a highly sensitive and skeleton selective multi-responsive chemosensor for Cu(II) and Pb(II)/Hg(II) ions

A set of triazole-based chromogenic and fluorescent chemosensors with amino acid/carbohydrate–fluorophore conjugates have been designed and synthesized. The metal cation-sensing properties of glycine–anthracene, C24H24O4N4 (3), glycine–pyrene C26H24O4N4 (4), glucose–anthracene, C32H33O10N3 (5) and glucose–pyrene, C34H33O10N3 (6) bio-conjugates have been studied systematically. The significant changes in their absorption spectra are accompanied by a strong color change from light yellow to brown for 3 and 4 and colorless to greenish blue for 5 and 6. Receptors 3 and 4 have potential in the “naked eye” detection of Cu2+ and 5 and 6 for Pb2+/Hg2+ ion. The receptors 3 and 4 show fluorescence diminution following Cu2+ coordination within the limit of detection at 0.89 parts per billion (ppb) and this is unprecedented, whereas the receptors 5 and 6 present drastic fluorescence quenching upon addition of Hg2+ and Pb2+ within the limit of detection at 4 and 2 ppb respectively. Interestingly, their fluorescence and colorimetric responses are preserved in the presence of water that can be used for the selective colorimetric detection of these ions in aqueous environments. Along with the spectroscopic data, combined 1H NMR titration of the complexes and the DFT studies suggest the proposed coordination modes.

Novel Class of Heterometallic Cubane and Boride Clusters Containing Heavier Group 16 Elements

Thermolysis of an in situ generated intermediate, produced from the reaction of [Cp*MoCl(4)] (Cp* = η(5)-C(5)Me(5)) and [LiBH(4).THF], with excess Te powder yielded isomeric [(Cp*Mo)(2)B(4)TeH(5)Cl] (2 and 3), [(Cp*Mo)(2)B(4)(μ(3)-OEt)TeH(3)Cl] (4), and [(Cp*Mo)(4)B(4)H(4)(μ(4)-BH)(3)] (5). Cluster 4 is a notable example of a dimolybdaoxatelluraborane cluster where both oxygen and tellurium are contiguously bound to molybdenum and boron. Cluster 5 represents an unprecedented metal-rich metallaborane cluster with a cubane core. The dimolybdaheteroborane 2 was found to be very reactive toward metal carbonyl compounds, and as a result, mild pyrolysis of 2 with [Fe(2)(CO)(9)] yielded distorted cubane cluster [(Cp*Mo)(2)(BH)(4)(μ(3)-Te){Fe(CO)(3)}] (6) and with [Co(2)(CO)(8)] produced the bicapped pentagonal bipyramid [(Cp*MoCo)(2)B(3)H(2)(μ(3)-Te)(μ-CO){Co(3)(CO)(6)}] (7) and pentacapped trigonal prism [(Cp*MoCo)(2)B(3)H(2)(μ(3)-Te)(μ-CO)(4){Co(6)(CO)(8)}] (8). The geometry of 8 is an example of a heterometallic boride cluster in which five Co and one Mo atom define a trigonal prismatic framework. The resultant trigonal prism core is in turn capped by two boron, one Te, and one Co atom. In the pentacapped trigonal prism unit of 8, one of the boron atoms is completely encapsulated and bonded to one molybdenum, one boron, and five cobalt atoms. All the new compounds have been characterized in solution by IR, (1)H, (11)B, and (13)C NMR spectroscopy, and the structural types were unambiguously established by crystallographic analysis of 2 and 4-8.

Synthesis and sensing properties of 1,1′-disubstituted unsymmetrical ferrocene-triazole derivatives: a multichannel probe for Hg(II) ion

Triazole-based unsymmetrically 1,1′-disubstituted ferrocene derivatives 4 and 5 have been synthesized using “click chemistry” with sequential functionalization at the cyclopentadienyl rings. The cation complexation properties of these ferrocene derivatives have been studied using electrochemical and spectroscopic techniques. The exceptional structural features present in these ligands are the presence of one cholesterol moiety, connected to the 1-position of the ferrocene center through a 1,2,3-triazole ring, and a fluorescent moiety, linked to the 1′-position of such a core through another triazole-ether linkage. Both the receptors experience perturbation of the CV in the presence of Hg2+ with a change of electrochemical potential (the large anodic shift ΔE1/2 = 129 mV for 4 and ΔE1/2 = 140 mV for 5). The changes in the absorption spectra are accompanied by the appearance of a new high energy (HE) peak at ca. 206 nm for 4 and 202 nm for 5 (4: e = 3123 × 102 M−1 cm−1, 5: e = 3140 × 102 M−1 cm−1) in the presence of Hg2+ ion. In addition, receptors 4 and 5 show colorimetric response and act as a selective “turn off” fluorescent receptor for Hg2+ and Cu2+ ions. On the basis of the 1H NMR titration, ESI-MS and DFT study, probable binding modes of 1,1′-disubstituted ferrocene derivatives 4 and 5 with Hg2+ have been proposed.

Novel triple-decker sandwich complex with a six-membered [B3Co2(μ4-Te)] ring as the middle deck.

Thermolysis of nido-[(Cp*Mo)2B4TeClH5], with an excess of Co2(CO)8 at room temperature, afforded a triple-decker sandwich complex [(Cp*Mo)2{μ-η(6):η(6)-B3H3TeCo2(CO)5}] (4), which represents an unsaturated 24-valence-electron sandwich cluster in which the middle deck is composed of B, Co, and a heavy group 16 element.

Hypoelectronic Dimetallaheteroboranes of Group 6 Transition Metals Containing Heavier Chalcogen Elements

We have synthesized and structurally characterized several dimetallaheteroborane clusters, namely, nido-[(Cp*Mo)2B4SH6], 1; nido-[(Cp*Mo)2B4SeH6], 2; nido-[(Cp*Mo)2B4TeClH5], 3; [(Cp*Mo)2B5SeH7], 4; [(Cp*Mo)2B6SeH8], 5; and [(CpW)2B5Te2H5], 6 (Cp* = η(5)-C5Me5, Cp = η(5)-C5H5). In parallel to the formation of 1-6, known [(CpM)2B5H9], [(Cp*M)2B5H9], (M = Mo, W) and nido-[(Cp*M)2B4E2H4] compounds (when M = Mo; E = S, Se, Te; M = W, E = S) were isolated as major products. Cluster 6 is the first example of tungstaborane containing a heavier chalcogen (Te) atom. A combined theoretical and experimental study shows that clusters 1-3 with their open face are excellent precursors for cluster growth reactions. As a result, the reaction of 1 and 2 with [Co2(CO)8] yielded clusters [(Cp*Mo)2B4H4E(μ3-CO)Co2(CO)4], 7-8 (7: E = S, 8: E = Se) and [(Cp*Mo)2B3H3E(μ-CO)3Co2(CO)3], 9-10 (9: E = S, 10: E = Se). In contrast, compound 3 under the similar reaction conditions yielded a novel 24-valence electron triple-decker sandwich complex, [(Cp*Mo)2{μ-η(6):η(6)-B3H3TeCo2(CO)5}], 11. Cluster 11 represents an unprecedented metal sandwich cluster in which the middle deck is composed of B, Co, and Te. All the new compounds have been characterized by elemental analysis, IR, (1)H, (11)B, (13)C NMR spectroscopy, and the geometric structures were unequivocally established by X-ray diffraction analysis of 1, 2, 4-7, and 9-11. Furthermore, geometries obtained from the electronic structure calculations employing density functional theory (DFT) are in close agreement with the solid state structure determinations. We have analyzed the discrepancy in reactivity of the chalcogenato metallaborane clusters in comparison to their parent metallaboranes with the help of a density functional theory (DFT) study.

A Homometallic Tricapped Cubane Cluster: [(Cp*Mo)4B4H4(μ4-BH)3] (Cp* = η5-C5Me5)

The reaction of [Cp*MoCl(4)] with an excess of LiBH(4), followed by thermolysis with tellurium powder in toluene, afforded a tricapped cubane cluster, [(Cp*Mo)(4)B(4)H(4)(μ(4)-BH)(3)] (1), which represents an unprecedented metal-rich metallaborane cluster with a cubane core containing 58 cluster valence electrons (cve) and three metal-metal bonds.

Unprecedented ferrocene–quinoline conjugates: facile proton conduction via 1D helical water chains and a selective chemosensor for Zn(II) ions in water

Two novel ferrocene–quinoline derivatives 3 (C22H19O2N3Fe) and 4 (C34H28O4N6Fe) have been synthesized and structurally characterized. Compound 3 exhibits good proton conductivity through 1D helical water chains. In addition, both compounds 3 and 4 selectively detect Zn2+ ions in water with a detection limit of 2 ppb through multiple channels.

Correction to Theoretical and Experimental Investigations on Hypoelectronic Heterodimetallaboranes of Group 6 Transition Metals

Density functional theory (DFT) has been used to probe the bonding and electronic properties of dimolybdaborane [(Cp*Mo)(2)B(5)H(9)], 1 (Cp* = η(5)-C(5)Me(5)), and several other heterodimolybdaborane clusters, such as [(Cp*Mo)(2)B(5)(μ(3)-OEt)H(7)] (2), [(Cp*Mo)(2)B(5)(μ(3)-OEt)(n-BuO)H(6)] (3), [(η(5)-C(5)H(5)W)(2)B(4)H(4)S(2)] (4), and [(Cp*Mo)(2)B(4)H(4)E(2)] (5-7, where, for 5, E = S, for 6, E = Se, and for 7, E = Te). The DFT results were also used to address some key points such as (i) the metal-metal bond length, (ii) the location and number of bridging and terminal hydrogen atoms, (iii) the molecular orbital analysis, and (iv) the assignment of (11)B and (1)H NMR chemical shifts. These studies further provide meticulous insight into similarities and differences between various dimetallaborane clusters 1-7. In addition, the crystal structures of 5 and 7 are reported, which come on top of the already existing literature of dimetallaboranes and support the theoretical findings.