ABSTRACT
The reaction of preassembled Cu(I) bimetallic units {Cu2(dppm)2} and {Cu2(dppa)2} (dppm: bis(diphenylphosphino)methane and dppa: bis(diphenylphosphino)amine) with pseudohalide linkers (azido, dicyanamide, and tricyanomethanide) allows for the quantitative and selective preparation of three discrete tetrametallic metallacycles of formula [Cu4(µ2-dppm)4(N3)2](PF6)2, [Cu4(µ2-dppm)4(N(CN)2)2](PF6)2, and [Cu4(µ2-dppm)4(C(CN)3)4]. To explore further the impact of the linker on the architecture and dimensionality of the molecular edifice, the study was extended to more sophisticated tetradentate cyanocarbanion ligands (tcnsMe-: 2-(methylthio)-1,1,3,3-propanetetracarbonitrile and tcnsEt-: 2-(ethylthio)-1,1,3,3-propanetetracarbonitrile). Three ladder-like one-dimensional coordination polymers and an octametallic metallacycle have been obtained. The careful comparison of the metric and geometrical intramolecular and intermolecular parameters observed in this series of seven derivatives allows for rationalization of their molecular architectures. The subtle balance between the length and steric hindrance of the ligand and the formation of noncovalent interaction networks greatly influences the topology and dimensionality of the resulting assemblies and will be discussed hereafter. The photophysical properties of these seven polymetallic Cu(I) compounds have also been also studied.
ABSTRACT
A ditopic Schiff base ligand, H2L has been synthesized and characterized by all spectroscopic techniques. It is highly selective and specific towards Al3+ in semi aqueous medium (DMF/H2O mixture) by exhibiting a drastic increase in the fluorescence intensity. The emission studies, spectroscopic data, life time and quantum yield results have been used to understand its binding mode, explore its specificity and establish its efficacy. The intensity difference is remarkable in physiological pH range. Due to its reversible behavior this ditopic fluorescent chemosensor can be used multiple times to make it cost effective. Detection limit for this chemosensor was found to be 0.65 µM. Experiments with TLC plates show that it can be used as a practical and portable sensor for studying environmental samples in real life. The L-Al3+ complex generated in the solution acts as a sensor to sequentially detect pyrophosphate groups present in inorganic pyrophosphates, ATP and ADP among other anions by turning off the fluorescence. Inhibit logic gate and its corresponding truth table has been developed to aid in further exploiting its multidimensional applications.
ABSTRACT
A pyrene-appended bipyridine hydrazone-based ligand, HL, was synthesized and characterized by spectroscopic methods. Upon complexation with Cu(ii), HL formed a hexanuclear paddlewheel metal-organic macrocycle (MOM) via self-assembly with a high association constant with the molecular formula of [Cu6L6(NO3)6]. Intermolecular and intramolecular π-π interactions were demonstrated in this hexanuclear Cu(ii) complex. Further, it was observed that HL had the potential to detect a trace level of Cu(ii) ion selectively among a wide range of biologically relevant metal ions in aqueous medium at physiological pH. Using HL, it was feasible to sense copper(ii) ions in living cells due to its good cell permeability and high solubility under physiological conditions along with its high IC50 value. The low detection limit, high sensitivity and good reproducibility make this Cu-sensor very promising. The complex (MOM) formed between the ligand and Cu(ii) was found to be 1 : 1 on the basis of fluorescence titrations and was confirmed by ESI-MS. Moreover, single-crystal study of the hexanuclear self-assembled fluorescent species provided better insight into its chemistry, e.g. coordination environment and binding mode, unlike most of the metal sensors due to the lack of a single-crystal structure of the metal sensor complex. Cytotoxicity assay and bioimaging were performed in living cells (Vero cells), giving green fluorescent images. Fluorescence lifetime measurements and theoretical calculations were carried out. The morphology and topographic details on the surface of the metal-organic macrocycle (MOM) were studied by field-emission scanning electron microscopy (FESEM).
ABSTRACT
Synthesis towards the preparation of an unsymmetrical binucleating Schiff-base ligand, (H2L) is discussed. It has been synthesized by reacting methyl 6-(hydrazinecarbonyl)picolinate with 2-hydroxy acetophenone. The ligand (H2L) comprises two different asymmetric binding pockets; however, when reacted with Mn(ii), Co(ii), Cu(ii) and Zn(ii) salts, very stable self-assembled [2 × 2] grid complexes form regardless of the employed metal-to-ligand ratio. The obtained complexes [Mn4L4]·(CH3CN) (1), [Co4L4]·(CHCl3) (2), [Cu4L4]·(CHCl3) (3) and [Zn4L4] (4) have been fully characterized by physicochemical methods, including ESI mass spectrometry and X-ray crystallographic analyses, and their EPR, magnetic and redox properties are discussed. All discussed complexes self-assembled in a 'head-to-tail' fashion leading to [2 × 2] grid architectures. Mn, Co and Cu grid complexes show weak to moderate antiferromagnetic coupling among the four metal centers. The high stability of the grid structures is in line with the lack of any observable dissociation or exchange between metal ions in solution. Complexes 1 and 2 show four quasi-reversible to irreversible oxidative responses in cyclic voltammograms at a glassy carbon working electrode in 1,2-dichlorobenzene and at a platinum working electrode in dichloromethane, respectively.
ABSTRACT
A new unsymmetrical ditopic ligand H2L was used to synthesize two [2 × 2] grid type tetranuclear trivalent and mixed-valent Fe, FeFe complexes, respectively. Both complexes [Fe(L')4] (1) and [FeFe(L)4](BF4)2·2CH3CN (2) have been X-ray structurally characterized. The magnetic properties of complexes 1 and 2 show dominant antiferromagnetic coupling. Mössbauer studies were carried out to confirm the electronic states of the iron centres. The structural properties of the two complexes are diverse though they have been synthesized from the same ligand but under different conditions. In 1, all the Fe(iii) metal centres are coordinated by two pairs of parallel but oppositely aligned ligand strands arranged in a 'head-to-tail' fashion, whereas in 2, Fe(ii) and Fe(iii) metal centres are coordinated by two pairs of parallel aligned ligand strands arranged in a 'head-to-head' fashion.
