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For practical applications, the development of bio-compatible organic molecules as p-block ion chemosensors is critical. Herein, we report the single crystal (SC) of new pyridine-pyrazole derived Al 3+ sensor H2PPC [( Z )- N '-(2,3-dihydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1 H -pyrazole-3-carbohydrazide] as well as its Cu-complex SC. The probe exhibits an "off-on" fluorescence response towards Al 3+ ions, and this has been modulated with different solvents. For selective detection of Al 3+ ions, a special coordination pocket in the structural backbone is advantageous. The chemosensor exhibits a submicromolar detection level (LOD = 4.78 μM) for Al 3+ . The density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations of H2PPC and [Al(HPP)2]+ (1) reveal that a change of the structural conformation of probe H2PPC upon complexation causes the pyrazole and pyridine units to create a specific cavity to tether Al 3+ , and consequently H2PPC proves to be a promising molecule for Al 3+ detection. Furthermore, the probe has been successfully used to evaluate Al 3+ as a low-cost kit using filter paper strips, and the in situ Al 3+ ion imaging in Vero cells as well as A549 cell lines shows the sensor's nuclear envelope penetrability, indicating that it has great potential for biological and environmental applications.

The homoleptic [2×2] tetranuclear compound [Cu4(PyPzCAP)4](NO3)4·8H2O (1) and the pentanuclear Mn(II) cluster [Mn5(PyPzCAP)6](ClO4)4·4C6H6 (2) are self-assembled from the ditopic pro-ligand HPyPzCAP [(5-methyl-1-(pyridin-2-yl)-N′-[1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazide)]. Complex 1 is almost a square grid, and all the Cu(II) centers show a distorted octahedral environment with an N4O2 chromophore. Complex 2 has a pentanuclear core with a trigonal bipyramidal arrangement of the Mn(II) atoms. The axial Mn centers bear an N3O3 chromophore and the equatorial centers have an N4O2 distorted octahedral arrangement. Complex 1 shows a ferromagnetic exchange interaction (J =+4.62cm−1 and g =2.05), whereas 2 shows weak an antiferromagnetic interaction (J =−2.73cm−1 and g =2.02). Both complexes 1 and 2 catalyze the allylic oxidation of cyclohexene to cyclohex-2-ene-1-one with good selectivity and an excellent overall turnover number. [ABSTRACT FROM AUTHOR]

Abstract: A pyrazole based ditopic ligand 5(E)-5-methyl-N′-(pyridin-2-ylmethylene)-1H-pyrazole-3-carbohydrazide (PzOPyH), prepared by the reaction between 5-methylpyrazole-3-carbohydrazide and pyridine-2-carbaldehyde, reacts with Mn(ClO4)2·6H2O to form a self-assembled, antiferromagnetically coupled alkoxide bridged pentanuclear Mn(II) homoleptic cluster complex [Mn5(PzOPy)6](ClO4)4 (1). The complex has a central Mn5(μ-O6) core involving six ligand molecules. This pentanuclear core has a trigonal bipyramidal arrangement of Mn(II) atoms, where, the axial metal centers (Mn2 and Mn_2) have a N3O3 chromophore and the equatorial centers (Mn1, Mn_1 and Mn3) have N4O2 chromophore with distorted octahedral arrangement around the metal centers. Intramolecular antiferromagnetic interaction between Mn(II) centers (J =−1.42, S =5/2) is the signature of the molecule. [Copyright &y& Elsevier]

Abstract: Pyrazole based ditopic ligand HL1 ((Z)-N′-(5-methyl-1H-pyrazole-3-carbonyl) picolinohydrazonamide) reacts with Cd(ClO4)2·6H2O and Zn(ClO4)2·6H2O to form a self assembled pentanuclear Cd(II) complex [Cd5(L1)6](ClO4)4 (1) and a mononuclear Zn(II) complex [Zn(HL1)2](ClO4)2 (2). On the other hand, HL2 ((Z)-N′-(5-methyl-1H-pyrazole-3-carbonyl) pyrazine-2-carbohydrazonamide) also forms a mononuclear [Zn(HL2)](ClO4)2(MeOH)2 (3) with Zn(ClO4)2.6H2O. All these complexes have been characterized crystallographically and spectroscopically. The Cd(II) complex (1) has a pentanuclear core with trigonal bipyramidal arrangement of Cd(II) atoms, where, the axial metal centers (Cd2 and Cd5) have N3O3 chromophore and the equatorial centers (Cd1, Cd3 and Cd4) have N4O2 chromophore with distorted octahedral arrangement around the metal centres. In 2 and 3, the NNO donor ligand molecules in their ketoimine form produce distorted octahedral environment around the Zn(II) centre with N4O2 chromophore utilizing pyridine/pyrazine N, one azomethine N and one carbohydrazide O atoms. Here, the pyrazole ring N atoms remain silent in coordination process. On the other hand, in 1, the same ligand HL1 coordinates in its deprotonated imineol form and functions as N3O donor, while, the pyrazole N atoms take part in coordination process. Ligands HL1 and HL2 are fluorescence silent but complexes 1, 2 and 3 show considerable fluorescence. The fluorescence intensity of 1 is higher than that of 2 and 3. [Copyright &y& Elsevier]

Abstract: Three new zig-zag 1D coordination polymers and a binuclear complex of Cu(II) involving pyrazole based tri- and pentadentate schiff base ligands (Z)-2-(2-(5-methyl-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L′1) and (Z)-2-(2-(5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L′2) are reported in this work. The ligand precursors L1 and L2 have been transformed into L1′ and L2′ during the course of reaction with metal ions in which the ester groups have been changed to carboxylate group. The 1D coordination polymers, namely, [Cu(L′1)(ClO4)2(H2O)] n (1), [Cu(L′2)(ClO4)] n (3), [Cu(L′2)(NO3)] n (4) and a binuclear complex [Cu2(L′1)2Cl2] (2) have been synthesized. The complexes 1–3 are of distorted octahedral geometry and the complex 2 is distorted square pyramidal. Interestingly, these structural variations are dependent on counterions and substituent on the pyrazole ring. These have been characterized by elemental analyses, UV, IR, single crystal X-ray diffraction, electrochemical and photoluminescence studies. L′1 serves as tridentate NNO donor where pyrazole nitrogen, azomethine nitrogen and ligand carboxylate group are coordinatively active, leaving the carbonyl oxygen of carbohydrazide part inactive. The same situation (coordination modes) arises in another pentadentate NNNOO donor L′2 where extra pyridine nitrogen is coordinated. The complexes 3 and 4 have considerable fluorescence emission while the rest of the complexes and the ligand molecules are fluorescent silent. [Copyright &y& Elsevier]

Abstract: The pyrazole based ditopic ligand PzCAP (HL, 5-methyl-N′-(1-(pyridine-2-yl)ethylidene)-1H-pyrazole-3 carbohydrazide) reacts with Ni(ClO4)2·6H2O, Zn(ClO4)2·6H2O and Cd(ClO4)2·6H2O to form a new alkoxide bridged binuclear Ni(II) complex [Ni2(PzCAP)3](ClO4)3·6(H2O) (1), a mononuclear Zn(II) complex [Zn(PzCAP)2](ClO4)(H2O) (2) and a self assembled pentanuclear Cd(II) complex [Cd5(PzCAP)6](ClO4)4(H2O) (3). These complexes have been characterized crystallographically and spectroscopically. In complex 1, the three ligand molecules display variable denticity towards the Ni(II) centers, one ligand behaves as tetradentate and two others behave as tridentate ligands to create distorted octahedral environments around the two Ni(II) centers, with N5O and N4O2 chromophores. In 2, the same ligand, using keto and enolic oxygen atoms, produces a distorted octahedral environment around the Zn(II) center with a N4O2 chromophore. Complex 3 has a pentanuclear core with a trigonal bipyramidal arrangement of Cd(II) atoms, where the axial metal centers (Cd2 and Cd4) have N3O3 chromophores and the equatorial centers (Cd1, Cd3 and Cd5) have N4O2 chromophores, with distorted octahedral arrangements around the metal centers. Interestingly, the pyrazole unit remains inactive to coordination for complex 2, whereas this unit takes part in coordination for 1 and 3. The ligand HL, complex 2 and complex 3 show fluorescence, while in 1 the fluorescence is substantially quenched compared to the ligand (HL) and its Zn and Cd complexes. As the ligand is capable of using different binding modes, according to the demands of the complex, the emission properties also change accordingly. [Copyright &y& Elsevier]

Abstract: A pyrimidyl-pyrazole based ditopic ligand N-[amino(pyridin-2-yl)methylidene]-1-(4,6-dimethylpyrimidin-2-yl)-5-methyl-1H-pyrazole-3-carbohydrazonic acid, PymPzOAP prepared by the reaction between pyrimidyl pyrazole 3-carbohydrazide and methyl ester of iminopicolinic acid, reacts with Cu(NO3)2·6H2O to form a self-assembled, ferromagnetically coupled alkoxide bridged tetranuclear homoleptic Cu(II)4 [2×2] grid complex [Cu4(PymPzOAP)4](NO3)4 (1). The complex has a central Cu4(μ-OR)4 core involving four ligand molecules. All the Cu(II) centers have N4O2 coordination environment with distorted octahedral geometry. Intramolecular ferromagnetic interaction between Cu(II) centers (J =4.94, S =4/2) is the signature of the molecule. [Copyright &y& Elsevier]

Abstract: A binuclear acylhydrazine bridged Cu(II) complex, [Cu2(L)(NO3)3(H2O)] (1), and an anti-orthogonal binuclear oxovanadium(V) complex, [V2O4(L)2] (2), have been synthesized and characterized spectroscopically and crystallographically. The ligand HL has two potentially bridging functional groups (μ-O, μ-N–N) and consequently can exist in the following coordination conformers: (a) metal centers bridged by μ-O, (b) metal centers bridged by μ-N–N. A rare acylhydrazine bridged (a) type configuration exists in the dinuclear Cu(II) complex 1. The bridging ligand mediates a strong antiferromagnetic coupling (J =−99cm−1). The exchange pathway parameters have also been evaluated from density functional theoretical calculations to corroborate the bridging signatures with experimental findings (J =−93.96cm−1). Molecule 2 has a centrosymmetric structure with each vanadium center having a distorted octahedral geometry. It shows a one step irreversible reduction at +0.43V. The bond angles, bond lengths and torsion angles in 2 are correlated with DFT. [Copyright &y& Elsevier]

Abstract: Varying coordination modes of the Schiff base ligand H2L [5-methyl-1-H-pyrazole-3-carboxylic acid (1-pyridin-2-yl-ethylidene)-hydrazide] towards different metal centers are reported with the syntheses and characterization of four mononuclear Mn(II), Co(II), Cd(II) and Zn(II) complexes, [Mn(H2L)(H2O)2](ClO4)2(MeOH) (1), [Co(H2L)(NCS)2] (2), [Cd(H2L)(H2O)2](ClO4)2 (3) and [Zn(H2L)(H2O)2](ClO4)2 (4), and a binuclear Cu(II) complex, [Cu2(L)2](ClO4)2 (5). In the complexes 1–4 the neutral ligand serves as a 3N,2O donor where the pyridine ring N, two azomethine N and two carbohydrazine oxygen atoms are coordinatively active, leaving the pyrazole-N atoms inactive. In the case of complex 5, each ligand molecule behaves as a 4N,O donor utilizing the pyridine N, one azomethine N, the nitrogen atom proximal to the azomethine of the remaining pendant arm and one pyrazole-N atom to one metal center and the carbohydrazide oxygen atom to the second metal center. The complexes 1–4 are pentagonal bipyramidal in geometry. In each case, the ligand molecule spans the equatorial plane while the apical positions are occupied by water molecules in 1, 3 and 4 and two N bonded thiocyanate ions in 2. In complex 5, the two Cu(II) centers have almost square pyramidal geometry (τ =0.05 for Cu1 and 0.013 for Cu2). Four N atoms from a ligand molecule form the basal plane and the carbohydrazide oxygen atom of a second ligand molecule sits in the apex of the square pyramid. All the complexes have been X-ray crystallographically characterized. The Zn(II) and Cd(II) complexes show considerable fluorescence emission while the remaining complexes and the ligand molecule are fluorescent silent. [Copyright &y& Elsevier]

The pyrazole based ligands (E)-2-(3,5-dimethyl-1H-pyrazol-1-yl)-N′-(pyridin-2-ylmethylene acetohydrazide (N-PzOPyH) and (E)-5-methyl-N′-(pyridin-2-ylmethylene)-1H-pyrazole-3-carbo hydrazide (PzOPyH), a 1:1 condensation product of 2-(3,5-dimethyl-1H-pyrazol-1-yl)aceto hydrazide and 5-methylpyrazole-3-carbohydrazide with pyridine-2-carbaldehyde respectively, and their keto oxygen bridged Cd(II) complexes [Cd 2 (N-PzOPy) 2 (H 2 O) 4 ](ClO 4 ) 4 ( 1 ), [Cd 2 (PzOPy) 2 (H 2 O) 4 ](ClO 4 ) 4 ( 2 ) and [Cd 2 (PzOPy) 2 (NO 3 ) 4 ] ( 3 )] are reported. They have been characterized structurally and spectroscopically. The potential tetradentate NONN-donor ligands N-PzOPyH and PzOPyH are engaged in the coordination around the cadmium(II) center through the nitrogen atoms of pyrazole, azomethine and pyridine and the ketonic oxygen atom of the carbohydrazide group to form complexes 1 , 2 and 3 , respectively. These ligands span themselves in the equatorial plane and the pentagonal bipyramidal geometry is completed around the metal centres (with an N 3 O 4 chromophore) with two apical water molecules (for 1 and 2 ) and with two nitrate ions (for 3 ). These keto bridged Cd(II) complexes are further stabilised by supramolecular interactions, like π⋯π, C–H⋯π and H-bonding interactions. [ABSTRACT FROM AUTHOR]

Abstract: Two new dinuclear copper compounds, [Cu2(pypz)2(N3)2(NO3)2] (1) and [Cu2(pypz)2(OH)2(NO3)2] (2), and one 1-D polymeric Cu(II) complex, [Cu(pypz)(dca)3] n (3) [‘pypz’=(3,5dimethyl-1-(2′-pyridyl)pyrazole) and dca=(dicyanamide)], have been synthesized and characterized crystallographically and spectroscopically. Complex 1 is pseudo-octahedral, adjacent Cu atoms are connected by a pair of μ(1,1) azido groups and the structure is stabilized by π–π interactions between two pyridyl moieties from two different neighboring complex molecules. Complexes 2 and 3 are square pyramidal. The hydroxo bridged complex 2 is further stabilized through H-bonding. The 1-D polymeric chain of 3 is bridged by an end-to-end dicyanamide bridge and it propagates along the crystallographic b axis, whilst the polymer chains are stacked one upon another along the crystallographic c axis. Low temperature magnetic measurement shows that complexes 1 and 2 are ferromagnetic (J values are 30.81 and 14.79cm−1, respectively), whereas due to larger Cu–Cu distances, complex 3 shows weak ferromagnetism. [Copyright &y& Elsevier]

Abstract: The anionic cis-dioxovanadium(V) complex species LVO2 − and L1VO2 − of two tridentate ONO ligands (H2L and H2L1) can bind alkali metal ions in a bis-monodentate fashion like a bridging carboxylate group. Here H2L (N′-[(E)-(2-hydroxyphenyl)methylidene]-3-methyl-1H-pyrazole-5-carbohydrazide) and H2L1 (N′-[(1E)-1-(2-hydroxyphenyl) ethylidene]-3-methyl-1H-pyrazole-5-carbohydrazide) are Schiff base ligands generated by the condensation of 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde and o-hydroxy acetophenone. The six products thus obtained are water soluble polymeric compounds in which the complementary units are held together by the simultaneous use of hydrogen bonding and coulombic interactions. [L1VO2Li(H2O)2]∞ (2), [LVO2Na(H2O)2]∞ (3) and [LVO2K(H2O)2]∞ (5) have been crystallographically characterized. Crystallographic characterization reveals that 2 and 3 are polymeric helicates and 5 is a polymeric cluster with L1VO2 − or LVO2 − units bridging the labile alkali metal ions which occupy positions on the axis of the polymeric chain. [ABSTRACT FROM AUTHOR]