NO Donor Ligand Research Articles

Synthesis, characterization and DFT studies of a new unsymmetrical dinuclear Vanadium(IV) complex with a bipodal N2O-donor ligand

A new dinuclear vanadium(IV) complex [(VO)2(μ-HBPA)2(μ-SO4)].4.75H2O was synthesized by the reaction between a bipodal N2O-donor ligand N-(2-hydroxybenzyl)-N-(pyridin-2-ylmethyl)amine (HBPA) and vanadyl sulfate. The complex was characterized by elemental analysis, thermogravimetric, electrochemical analysis, ESI-MS, FT-IR and UV–visible. The structure was determined by single crystal X-ray diffraction. The two non-equivalent vanadium(IV) ions are hexacoordinated being bridge-coordinated by the oxygen atoms from of HBPA and sulfate group. The complex was studied by DFT calculations and showed high polarity.

Synthesis and characterization of new galactosylated-based N2O-donors tridentate ligands

AbSTRACTThe synthesis and characterization of three novel N2O-donor ligands containing the group 4-[1-β-d-2,3,4,6-tetra-O-acetyl-galactosyl)]benzaldehyde are presented. The insertion of this group was designed to increase the absorption of the prodrug in tumor cells, and is part of an ongoing work in our group with tridentate ligands to develop potential cobalt(III) prodrugs. The synthetic route described here allowed the isolation of pure ligands with yields ranged 81-89%. Finally, compounds were characterized by IR, NMR and HRMS (ESI+).

Tri-nuclear copper-cadmium complexes of a N2O2-donor ligand with the variation of counter anions: Structural elucidation and theoretical study on inter-molecular interactions

Four new tri-nuclear hetero-metallic copper(II)-cadmium(II) complexes [(CuL)2CdCl2] (1), [(CuL)2CdBr2] (2), [(CuL)2CdI2] (3) and [(CuL)2Cd(NO3)2] (4) have been synthesized using [CuL] as ‘‘ligand complex’’ (where H2L = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine) and characterized by elemental analysis, IR, UV–Vis spectroscopy and single crystal X-ray diffraction studies. Crystal structure analyses reveal that all four complexes consist of a tri-nuclear moiety in which two square-pyramidal [CuL] units are bonded to a central Cd(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate octahedral environment being bonded additionally to two mutually trans chloride (in 1), bromide (in 2), iodide (in 3) and oxygen atoms of nitrate (in 4) ions. Presence of several non-covalent interactions (i.e. π···π, CH···O and Cu···Cu interactions) has been observed in the crystal packing of all the four molecules that assist the formation of 1D supramolecular assemblies in the solid state. The interactions were investigated by means of high level DFT calculations (PBE0-D3/def2-TZVP) with the help of TURBOMOLE 7.0 program, characterized using Bader’s theory of “atoms-in-molecules” (AIM) and rationalized using molecular electrostatic potential (MEP) surface calculations.

Crystal structure and magneto-structural investigation of alkoxido bridged dinuclear Fe(III) complexes with 1,3-oxazolidine ligands

Four 1,3-oxazolidine based ligands (H2L1−H2L4) were synthesized in solvent-free condition from the reaction of amino alcohols (2-amino-2-(hydroxymethyl)-1,3-propanediol or 2-amino-2-ethyl-1,3-propanediol) and 2-acetylpyridine or 2-pyridinecarboxaldehyde at 110 °C. Four new dinuclear Fe(III) complexes, [Fe2(HL1)(N3)4] (1), [Fe2(HL2)(N3)4] (2), [Fe2(HL3)(N3)4] (3) and [Fe2(HL4)(N3)4] (4), were synthesized with a similar procedure by the reaction of H2L1–4, Fe(NO3)3·9H2O and NaN3 in 1:1:2 molar ratios in methanol. The ligands and complexes were characterized by elemental analysis and spectroscopic methods. The structure of complexes was solved by single-crystal X-ray diffraction analysis which showed complexes 1–4 to be alkoxido-bridged dinuclear Fe(III) complexes. The structural studies indicated that the crystal structure of 2, 3 and 4 consist of a centrosymmetric dinuclear Fe(III) complexes while the asymmetric unit in 1 consists of two halves of the two independent molecules. The Fe(III) ions have similar coordination environments (cis-FeN4O2) in all of 1–4 which can be described as distorted octahedral geometry. The 1,3-oxazolidine ligands act as mononegative tridentate N2O-donor ligand in 1–4. Two azide groups are also coordinated to each Fe(III) ion as terminal monodentate ligands. The alcoholic arms of the 1,3-oxazilidine ligands act as bridging groups between Fe(III) ions and the Fe⋯Fe distances through these bridges are in the range of 3.157–3.198 Å. Magnetic studies in 2–300 K range reveal antiferromagnetic interactions between the Fe(III) ions with values for the magnetic coupling constants in the range −9.4 cm−1 to −9.7 cm−1, with H = −2J(S1S2).

Mononuclear lanthanide complexes assembled from a tridentate NNO donor ligand: design of a DyIII single-ion magnet.

The reaction of a tridentate NNO donor ligand, 4-nitro-2-((2-(pyridine-2-yl)hydrazono)methyl)phenol (HL) with lanthanide(iii) nitrates in the presence of triethylamine afforded a new family of neutral mononuclear LnIII complexes [Ln(NO3)(L)2(HOCH3)] (Ln = Gd; (1) Tb; (2), Dy; (3), and Ho (4). The mononuclear complexes were structurally characterized by single crystal X-ray diffraction studies which revealed a spherical tricapped trigonal prism geometry with a pseudo D3h symmetry around the LnIII centre. Static (dc) and dynamic (ac) magnetic studies have been performed on these complexes. Field-induced single-ion magnet behaviour was observed in the DyIII analogue with an effective energy barrier and an pre-exponential factor of Δ/kB = 68(2) K and τ0 = 1.8 × 10-7 s, respectively.

Catalytic oxidation of benzyl alcohols by new Cu(II) complexes of 1,3-oxazolidine based ligand obtained from a solvent free reaction

A new 1,3-oxazolidine based ligand, (2-pyridin-2-yl-1,3-oxazolidine-4,4-diyl)dimethanol (H3L), has been synthesized from the reaction of 2-amino-2-(hydroxymethyl)-1,3-propanediol and 2-pyridinecarboxaldehyde at 110 °C. Two mononuclear Cu(II) complexes, [Cu(H3L)Cl2]·CH3OH (1) and [Cu(H3L)2]·2Cl (2), have been synthesized with a similar procedure by the reaction of H3L and CuCl2·H2O in 1:1 and 2:1 M ratios in methanol. The ligand and complexes have been characterized by elemental analysis and spectroscopic methods. The structure of complexes has been characterized by single-crystal X-ray diffraction analysis which showed the copper ion has a distorted square pyramidal geometry in 1 and distorted octahedral geometry in 2. The 1,3-oxazolidine ligand acts as a neutral tridentate N2O-donor ligand in both 1 and 2. Two chloride anions remain coordinated to Cu(II) ion in complex 1, but they act as counter ions in complex 2. The catalytic activity of these complexes has been investigated in the oxidation of benzyl alcohol by using H2O2 or TBHP as oxidant. The effects of some influential parameters in catalytic reactions like molar ratio of oxidant-to-substrate, temperature, nature of oxidant and solvent have been studied to obtain the optimum condition. Moreover, the effects of chlorine substituent on the phenyl group (ortho-, meta- and para-positions) has also been explored. The results of these studies show that both 1 and 2 catalyze the oxidation of benzyl alcohol derivatives to the corresponding benzaldehydes and a little amount of the related benzoic acids, produced by over oxidation of benzaldehyde, are also detected in the reaction mixtures. The results indicate that the selectivity and the activity of these catalytic systems depend on the reaction conditions and the steric and electronic properties of the reagents.

Functional mimics of type-2 and type-3 copper oxidases: Self-assembled molecular association in mononuclear copper(II) complex enhances the catalytic activity

Mononuclear copper(II) complexes [Cu(L1/L2)(pybzim)](ClO4) (1–2), where H(L1)/H(L2) is tridentate NNO donor ligand and pybzim is 2-(2-pyridyl)benzimidazole, have been isolated. The X-ray crystal structure of 1 possesses a CuN4O chromophore with distorted square pyramidal geometry. It displays self-assembled molecular association viz., (a) intermolecular N-H⋅⋅⋅O hydrogen bonding, (b) inter-pair π-π anti-parallel stacking and (c) attractive C-H⋅⋅⋅π non-covalent interactions. The complexes are catalytically effective in the oxidation of ascorbic acid to dehydroascorbic acid, benzylamine to benzaldehyde and 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-quinone, thus modeling the activity of type-2 and type-3 copper oxidases.

Slow relaxation of magnetization in a bis-mer-tridentate octahedral Co(ii) complex.

Reaction of a rigid tridentate ligand o-[(1H-imidazol-2-yl)methylideneamino]phenol (2-H2imap) with Co(ClO4)2 in the presence of NaN3, or Co(NO3)2 without a base yields [CoII(2-Himap)2] 1 and [CoIII(2-Himap)2]NO3·MeOH 2, respectively. Both complexes exhibit a mer-octahedral geometry with the cobalt centre being distorted along an octahedral-trigonal prismatic pathway. The packing in 1 and 2 is dominated by H-bonding forming 2D sheets and 1D chains, respectively. Detailed dc and ac magnetic studies indicate that 1 is a field-induced single-ion magnet (SIM) with D = 36.7 cm-1 and E = 2.0 cm-1. Extensive ab initio calculations support these conclusions and suggest that relaxation of the magnetization occurs principally through direct quantum tunnelling in the ground state, with the Raman process dominant in an applied field. This contrasts with the recently reported series of mer-[Co(L)2] (L = monoanionic NNO donor ligand; Inorg. Chem., 2017, 56, 6056-6066) complexes where D is negative, as these compounds have a more ambiguous geometry, and highlights the importance of supramolecular interactions in subtly altering the coordination sphere thereby impacting the magnetic behaviour.

Tri- and hexa-nuclear NiII-MnII complexes of a N2O2 donor unsymmetrical ligand: synthesis, structures, magnetic properties and catalytic oxidase activities.

A new mononuclear Ni(ii) complex, [NiL] (1) of an unsymmetrically dicondensed N2O2 donor ligand, H2L (where H2L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine), has been synthesized. Complex 1, on reaction with Mn(ii) in the presence of different co-anions, yielded three heterometallic NiII-MnII complexes, [(NiL)2Mn(NCS)2]·CH3CN (2), [(NiL)2Mn(N3)(H2O)](ClO4)·H2O (3) and [{(NiL)2Mn(H2O)}2(μ1,3-N3)](ClO4)3 (4). Single crystal structural analyses show that complexes 2 and 3 contain similar bent trinuclear NiII2MnII structures, with the difference that in complex 2 two SCN- ions and in 3, one N3- and one H2O molecule are coordinated to the Mn(ii) centre. Complex 4 possesses a hexanuclear structure, in which two trinuclear NiII2MnII units are connected via a single μ1,3-azido bridge. Variable temperature dc molar magnetic susceptibility measurements reveal that the two Mn(ii) centres in complex 4 are antiferromagnetically coupled with an exchange coupling constant (J) of -3.73 cm-1. Among the three heterometallic complexes, only 3 and 4 show bio-mimetic catalytic oxidase activities. For catecholase like activity, the turnover numbers (Kcat) of complexes 3 and 4 are 984 and 2081 h-1, respectively, whereas for phenoxazinone synthase-like activity, the turnover numbers of complexes 3 and 4 are 6351 and 10 545 h-1, respectively. The high catalytic oxidase activities of complexes 3 and 4 in contrast to the inactivity of complex 2 are attributed to the coordination of a water molecule to the Mn(ii) centre in the former structures, which facilitates the binding of the substrate with the catalyst. Mass spectral analyses suggest the probable formation of a complex-substrate intermediate in these catalytic reactions and cyclic voltammetry measurements show that Ni(ii) is reducible to Ni(i).

Synthesis, characterization, electrical conductivity and luminescence properties of two copper(II) complexes with tridentate N2O chelating ligands containing imine bond

In the present study, we describe the synthesis and characterization of two tridentate N2O donor ligands, namely, (E)-2-(((2-(diethylamino)ethyl)imino)methyl)-6-methoxyphenol (HL1) and (E)-2-(((2-(diethylamino)ethyl)imino)methyl)-6-ethoxyphenol (HL2), and their copper(II) complexes, [Cu(L1)(CH3COO)] (1), [Cu(L2)(CH3COO)] (2). They have been synthesized under conventional methods and characterized by elemental analysis, FTIR, 1H and 13C NMR, ICP-OES, TGA and GC/MS analysis. For the morphological analysis field emission scanning electron microscopy (FESEM) was used. The geometry of the copper(II) complexes was determined by single crystal X-ray diffraction analysis. The copper(II) ions are in distorted square-pyramidal coordination environments. Complexes crystallize in monoclinic space group, P21/c. The electrical conductivity and luminescence properties of 1–2 have been investigated.

A uranium(VI) complex with a tetradentate N1,N4-disalicyliden-S-ethylisothiosemicarbazone ligand

The Schiff base ligand of bis-(2-hydroxybenzaldehyde)-S-ethylisothiosemicarbazone and its U(VI) complex have been prepared. Their structures were fully characterized by elemental analysis, FT-IR, molar conductivity, UV–Vis and 1H NMR methods. X-ray diffraction has been used to determine the molecular structure of the uranium complex. The Schiff base complex was found to be pentagonal bipyramidal. The N2O2 donor ligand was coordinated to the metal center as a tetradentate binegative agent. Computational studies were performed using the DFT method to estimate the structural preferences in tridentate and tetradentate isothiosemicarbazones. Geometry optimization and natural bond orbital analyses of the UO2(II) complex have been further discussed in detail. The thermal stabilities of the ligand and its uranium complex have also been determined by thermogravimetric analysis (TGA).

Synthesis, characterization, EPR spectroscopy and catalytic activity of a new oxidovanadium(IV) complex with N2O2-donor ligand

A new oxidovanadium(IV) complex, 2[VOL(OH2)] CH3OH (1), was synthesized from the reaction of VO(acac)2 with a symmetric N,O-donor Schiff base ligand (H2L), in which H2L is 6,6'-((1E,1′E)-((2-hydroxypropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol). The compounds were characterized by elemental analysis and spectroscopic methods. The molecular structure of complex was determined by single-crystal X-ray analysis which indicated that the crystal packing of complex contains two independent mononuclear vanadium complexes connected together by several strong hydrogen bonding interactions. The EPR spectrum of powdered complex 1 at liquid helium temperature showed two intensive octets which proved to be associated with V4+ ions with 3d1 electronic configuration. From EPR spectrum the values of the parameters: g|| = 1.9454 ± 0.0004, g⊥ = 1.9491 ± 0.0004, A|| = 0.0084 ± 0.0008 cm−1 and A⊥ = 0.0033 ± 0.0006 cm−1 were calculated for this complex. Complex 1 was employed as catalyst for oxidation of cyclooctene in the presence of H2O2 as oxidant. In order to obtain the suitable condition of catalytic oxidation, the effect of various parameters including the amount of the catalyst, temperature and solvent was studied. The results of catalytic studies showed that complex 1 can provide an effective and selective catalytic system for epoxidation of cyclooctene.

Facile synthesis and vapochromic studies of Co(II) complexes bearing NO and OO donor ligands

Two Co(II) complexes containing malonic and isonicotinic acids have been prepared by manual grinding of stoichiometric amounts of the starting materials. Elemental analysis (CHN), IR, UV-vis spectroscopic techniques, TGA-DTG investigation and X-ray powder diffraction analysis were used to characterize the two compounds. Isonicotinic acid coordinated to the metal via the pyridine ring nitrogen and one oxygen atom of the carboxylic group while malonic acid coordinated via both oxygen atoms of the carboxylate groups indicating bidentate coordination mode in the two compounds. The compounds were exposed to some volatile organic compounds (VOCs) containing nitrogen or oxygen donor atoms in the solid state and their vapochromic behaviours studied using colour changes, FT-IR and solid state UV-vis spectroscopies. Heating the samples exposed to the VOCs for a few minutes at 100 °C regenerates the original material without degradation, even after several heating cycles.

Mono- and di-nuclear nickel(ii) complexes derived from NNO donor ligands: syntheses, crystal structures and magnetic studies of dinuclear analogues

Ferromagnetic interaction in dinickel(ii) complexes, supported by DFT calculations, is reported. Bis(phenoxo)-bridged compound is only the second example of ferromagnetically coupled system.

Spin-crossover in a homoleptic cobalt(ii) complex containing a redox-active NNO ligand

We report the structural and variable temperature magnetic properties of divalent cobalt complex containing the ligand 1-(2-pyridylazo)-2-phenanthrol (papl). This complex provides a rare example of spin-crossover in cobalt complexes with redox-active NNO donor ligands.

Synthesis, X-ray characterization, DFT calculations and Hirshfeld surface analysis of Zn(ii) and Cd(ii) complexes based on isonicotinoylhydrazone ligand

In this manuscript we report the synthesis and X-ray characterization of four Zn(II) complexes and three Cd(II) complexes with an asymmetrical hydrazone–pyridine based ligand {HL = 2-acetyl-pyridyl-isonicotinoylhydrazone (HAPIH)}; i.e. {[Zn(HL)2](NO3)2·H2O} (1), [Zn(HL)Br2] (2), [Zn(HL)I2] (3), [Zn(HL)(NCS)2] (4), [Cd(L)2] (5), {[Cd(HL)Br2]·CH3OH} (6) and {[Cd(HL)I2]·2CH3OH} (7). The Schiff base acts as a tridentate N2O-donor ligand through the oxygen, the imine and pyridine nitrogen atoms in all the complexes. In most complexes, the ligand is observed to coordinate as a zwitterion since the proton in the hydrazine group (N–NH–CO) shifted to the uncoordinated pyridine ring, except in 7. On the other hand, in 5 the ligand acts as a negatively charged species and is bound to the cadmium center in the enolic form (N–NC–O−). In complexes 2–4, 6 and 7, the coordination geometry around each metal center is distorted trigonal bipyramidal, with the coordination sphere of the metal completed by two halide or NCS anions. On the other hand, in homoleptic complexes 1 and 5, the metal, chelated by two tridentate Schiff base ligands, exhibits an octahedral geometry. In the crystal packing of all compounds, the pyridine rings favour π–π interactions among the symmetry related complexes. The noncovalent interactions among the complexes have been analyzed using Hirshfeld surface analysis and DFT calculations using Grimme's D3 dispersion correction to properly describe the π–π interactions.

New NO donor ligands and complexes containing furfuryl or crown ether moiety: Syntheses, crystal structures and tautomerism in ortho-hydroxy substituted compounds as studied by UV–vis spectrophotometry

NO donor ligands were prepared by the condensation of methoxy substituted salicylaldehyde with 5-methylfurfurylamine (1 and 2) and 4′-aminobenzo-15-crown 5 (3–5). New crown ether ligands of Schiff base type (3–5) containing recognition sites for alkali metal and transition guest cations. Ni(II) complexes (1a–5a) have been synthesized with bidentate NO donor Schiff base ligands (1–5) with Ni(CH3COO)2.·4H2O. Monotopic crystalline 1:1 (Na+:ligand) sodium complexes (3b–5b) of the crown ether ligands were also prepared. Schiff bases (1–5) and complexes (1a–5a, 3b–5b) were characterized by elemental analyses, FT-IR, 1H-, 13C-NMR and mass spectroscopies. The crystal structures of 1, 1a and 2 were verified by X-ray diffraction analysis. The tautomeric equilibria (phenol-imine, O–H⋯N and keto-amine, O⋯H–N forms) have been systematically studied by using UV–vis spectrophotometry for the o-hydroxy substituted compounds (1–5). The UV–visible spectra of these ligands (1–5) were recorded and commented in polar, non-polar, acidic and basic media.

Synthesis, structural characterization, and catalytic reactivity of a new molybdenum(VI) complex containing 1,3,4-thiadiazole derivative as a tridentate NNO donor ligand

A new cis-dioxo molybdenum(VI) complex was obtained by reaction of 2,4-dihydroxybenzylidene(5-N,N-methylphenylamino-1,3,4-thiadiazol-2-yl)hydrazone as ligand and [MoO2(acac)2] in methanol and was characterized by elemental analyses, 1H NMR, IR, and electronic spectroscopic studies. The complex was also analyzed by single-crystal X-ray diffraction. The structure determination revealed a distorted octahedral coordination geometry around molybdenum in which the tridentate NNO donor (L2–) is bonded to [MoO2]2+ through phenolic oxygen, hydrazinic nitrogen, and thiadiazole nitrogen. The sixth coordination site is occupied by a weakly bonded methanol. The complex was tested as a catalyst for homogeneous epoxidation of olefins using tert-butyl hydrogen peroxide as an oxidant. In the homogeneous catalytic system, the reactions are efficiently carried out with high yields and selectivity.

Cis-{MoO2}(2+) assisted Mannich-type addition of acetylacetonate methine to the azomethine of tridentate Schiff bases: racemic complexes with chiral transformed ligands.

Reactions of [MoO2(acac)2] (acac(-) = acetylacetonate) with the potential N2O-donor 5,5-membered fused chelate rings forming Schiff bases 2-(2-pyridylaldimine)ethanol (HL(1)) and 4/5-R-2-(2-pyridylaldimine)phenols (HL(n); n = 2-5 for R = H, 4-Cl, 4-Me and 5-Me, respectively) lead to the facile formation of racemic complexes of the general formula cis-[MoO2(acacL(1-5))] () in 80-85% yield. Here, (acacL(n))(2-) represents a chiral N2O2-donor ligand system formed by a novel Mannich-type reaction that involves acetylacetonate and the azomethine fragment of HL(n) both coordinated to the cis-{MoO2}(2+) unit. The characterization of has been performed with the help of microanalytical (CHN), spectroscopic (ESI-MS, IR, UV-Vis and (1)H- and (13)C-NMR) and electrochemical measurements. The molecular structures of all the complexes except for are authenticated by single crystal X-ray crystallography. The Mo(vi) center in each of these analogous complexes is in a distorted octahedral N2O4 coordination sphere assembled by the chiral N2O2-donor transformed ligand (acacL(n))(2-) and the two mutually cis-oriented oxo ligands. In the crystal lattice, each of exists as a centrosymmetric discrete dimer via a pair of reciprocal N-HO hydrogen bonds between its enantiomeric pairs.

Synthesis, biological and comparative DFT studies on Ni(II) complexes of NO and NOS donor ligands

Three new NOS donor ligands have been prepared by addition ethanolic suspension of 2-hydrazino-2-oxo-N-phenyl-acetamide to phenyl isocyanate (H2PAPS), phenyl isothiocyanate (H2PAPT) and benzoyl isothiocyanate (H2PABT). The Ni(II) complexes prepared from the chloride salt and characterized by conventional techniques. The isolated complexes were assigned the formulaes, [Ni2(PAPS)(H2O)2](H2O)2, [Ni(H2PAPT)Cl2(H2O)](H2O)2 and [(Ni)2(HPABT)2Cl2(H2O)2], respectively. The IR spectra of complexes shows that H2PAPS behaves as a binegative pentadentate via both CO of hydrazide moiety in keto and enol form, enolized CO of cyanate moiety and the CN (azomethine) groups of enolization. H2PAPT behaves as neutral tridentate via both CO of hydrazide moiety and CN (azomethine) group due to SH formation and finally H2PABT behaves as mononegative tetradentate via CO and enolized CO of hydrazide moiety, CO of benzoyl moiety and CS groups. The experimental IR spectra of ligands are compared with those obtained theoretically from DFT calculations. Also, the bond lengths, bond angles, HOMO (Highest Occupied Molecular Orbitals), LUMO (Lowest Unoccupied Molecular Orbital) and dipole moments have been calculated. The calculated HOMO–LUMO energy gap reveals that charge transfer occurs within the molecule. The theoretical values of binding energies indicate the higher stability of complexes than of ligands. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats–Redfern and Horowitz–Metzger methods. The antibacterial activities were also tested against B. Subtilis and E. coli bacteria. The free ligands showed a higher antibacterial effect than their Ni(II) complexes. The antitumor activities of the Ligands and their Ni(II) complexes have been evaluated against liver (HePG2) and breast (MCF-7) cancer cells. All ligands were found to display cytotoxicity that are better than that of Fluorouracil (5-FU), while Ni(II) complexes show low activity.