Synthesis, chemical speciation and SOD mimic assays of tricarballylic acid-copper(II) and imidazole-tricarballylic acid-copper(II) complexes

The coordination behavior of copper(II) with tricarballylic acid (H₃TCA) and imidazole (Imz) is described. Speciation in aqueous solution has been determined at 25 °C and 0.15 M NaCl ionic strength by potentiometric measurements and EPR characterization of the species. Two new compounds CuTCAH · 3H₂O and CuTCAHImz · 2H₂O were obtained and characterized by elemental analysis diffuse reflectance, FTIR (Fourier transform infrared spectroscopy), EPR and thermal behavior. Their in vitro superoxide dismutase-mimetic activities have been tested.     

Polynuclear and polymeric metal complexes based upon 1,2,4-triazolyl functionalized adamantanes

A series of coordination compounds [Cd₂(trad)₇Br₂][Cd(trad)Br₃]₂ (1), [Cd₃(trad)₆{N(CN)₂}₄(H₂O)₂](N(CN)₂)₂ (2), [{Cd₂(trad)₅}{Cd(N(CN)₂)₆}]·3CH₃OH (3), [{Cd₃(trad)₆(SeCN)₂}{Cd(SeCN)₄}₂] (4), [Cd₂(trad)₃(NCS)₄] (5), [Cd₃(tr₂ad)₃(μ-NCS)₃](NCS)₃ (6), [Cd₃(tr₂ad)₆](NO₃)₆·22H₂O (7), [Cu₃(tr₂ad)₄(SO₄)(H₂O)₃](SO₄)₂·34H₂O (8) and [Cu₂(OH)(tr₂ad)₂](NO₃)₃·4H₂O (9) (trad = 4-(adamantan-1-yl)-1,2,4-triazole; tr₂ad = 1,3-bis(1,2,4-triazol-4-yl)-adamantane) revealed the potential of 1,2,4-triazolyl functionalized adamantanes for design of metal-organic polymers incorporating polynuclear coordination units as multiconnected nodes. Structures 1-5 are based upon characteristic di- and trinuclear clusters involving triple triazole bridges [M(μ₂-trad)₃M] (M = Cd), while doubling of the ligand functionality (tr₂ad) allows integration of the clusters into 3D polymeric frameworks 6-9 (M = Cd, Cu).     

New yttrium(III) and copper(II) coordination polymers with partially protonated cyclohexane-1,2,3,4,5,6-hexacarboxylato ligands: Synthesis, crystal structures and properties

Two coordination polymers, [Y(H₂O)₄(H₃chhc)]·6H₂O (1) and [Cu₅(H₂O)₁₀(Hchhc)₂]·4H₂O (2) with H₆chhc = cyclohexane-1,2,3,4,5,6-hexacarboxylic acid) represent rare examples of metal complexes with partially protonated cyclohexane-1,2,3,4,5,6-hexacarboxylato ligands. The [Y(H₂O)₄]³⁺ units in 1 are interlinked by the triprotonated (H₃chhc)³⁻ anions in a η⁵μ₄ bridging mode to form 2D (4³)₂(4⁶·6⁶·8³) topological networks, which are stacked along [0 1 0] direction in ···ABAB··· fashion with the lattice H₂O molecules sandwiched between layers. The pentameric [Cu₅(H₂O)₁₀]¹⁰⁺ units in 2 are bridged by monoprotonated (Hchhc)⁵⁻ anions in a η⁸μ₆ fashion to generate a 3D MOF of an unprecendented (4³)(4⁵·6⁷·8³) topology with the lattice H₂O molecules in channels. The temperature-dependent magnetic susceptibility data of 2 could be modeled to a combination of a linear chain of equally-spaced Cu(II) ions (J₁ = 1.86 cm⁻¹) with an isosceles triangular Cu₃ unit (J₂ = 5.86 cm⁻¹).     

Hydrothermal syntheses, structures and properties of five rare earth coordination polymers with (1,3,4-thiadiazole-2,5-diyldithio)diacetic acid

Hydrothermal reactions of rare earth ions(III) with a flexible building unit (1,3,4-thiadiazole-2,5-diyldithio)diacetic acid (H₂tzda) lead to five novel coordination polymers with 1D chain and 3D network structures, namely, {[Y₂(tzda)₃(H₂O)₁₀] · 5H₂O}_n (1) and [Ln₂(tzda)₃(H₂O)₅]_n [Ln = Er (2), Pr (3), Nd (4), Eu (5)]. Compound 1 has one-dimensional ribbon-like chain structure constructed by [Y₂(tzda)₃] units through the syn-anti bidentate bridging mode of carboxylate groups. Compounds 2-5 possess compact three-dimensional network structures which are made up of [Ln₂(tzda)₃] (Ln = Er, Pr, Nd and Eu) units bridged by carboxylate groups. In these compounds, the flexible tzda²⁻ ligand is versatile and displays six different coordination fashions to meet the requirement of the coordination preference of the metal center. Furthermore, the magnetic behaviors for 2-5 in the temperature range of 5.0-300 K and photoluminescent property of 5 are significantly investigated in this paper.     

Zinc complexes of the antibacterial drug oxolinic acid: Structure and DNA-binding properties

The neutral mononuclear zinc complexes with the quinolone antibacterial drug oxolinic acid in the absence or presence of a nitrogen donor heterocyclic ligand 2,2′-bipyridine or 1,10-phenanthroline have been synthesized and characterized. The experimental data suggest that oxolinic acid is on deprotonated mode acting as a bidentate ligand coordinated to the metal ion through the ketone and one carboxylato oxygen atoms. The crystal structures of (chloro)(oxolinato)(2,2′-bipyridine)zinc(II), 2, and bis(oxolinato)(1,10-phenanthroline)zinc(II), 3, have been determined with X-ray crystallography. The biological activity of the complexes has been evaluated by examining their ability to bind to calf-thymus DNA (CT DNA) with UV and fluorescence spectroscopies. UV studies of the interaction of the complexes with DNA have shown that they can bind to CT DNA and the DNA-binding constants have been calculated. Competitive studies with ethidium bromide (EB) have shown that complex 3 exhibits the ability to displace the DNA-bound EB indicating that it binds to DNA in strong competition with EB.     

Synthesis and magnetic characterization of Ln(III) complexes with 4,4′-bipyridine and crotonato as bridging ligands

The crystal structure and magnetic characterization of an isostructural series of general formula {[Ln(crot)₃(H₂O)(bpy)_1/2]₂}_n (crot, crotonate (C₄H₅O₂); bpy, 4,4′-bipyridine (C₁₀H₈N₂); Ln, Nd, Gd, Ho, Er, Y) is presented. The ninefold Ln coordination polyhedra form dimeric entities that are connected throughout the bpy units into infinite polymeric chains. All (but the yttrium) reported compounds present a weak antiferromagnetic interaction connecting metal centres.     

Syntheses, structures, and photoluminescent properties of four d metal-quinolinato coordination polymers with similar rod-like SBUs

Four M^II quinolinato complexes, [Zn₂(quin)₂(H₂O)₃]_n (1), [Zn(quin)(H₂O)₂]_n (2), [Zn(quin)(H₂O)]_n (3) and [Cd(quin)]_n (4) (H₂quin = 2,3-pyridinedicarboxylic acid or quinolinic acid), have been hydrothermally synthesized and structurally characterized. X-ray diffraction analyses reveal that all of these four complexes are constructed from similar rod-like SBUs, [M(quin)]_n (M = Zn or Cd). Complexes 1 and 2 have similar 1-D box-like chains but different packing structures; complex 3 has a 2-D grid-like network and complex 4 has an unusual 2-D bilayer structure. Due to the different structural features, these complexes exhibit different photoluminescent emissions: complex 1 at 439 nm (λ_ex = 345 nm), complex 2 at 428 nm (λ_ex = 360 nm), complex 3 at 508 nm (λ_ex = 304 nm) and complex 4 at 500 nm (λ_ex = 324 nm).     

Crystal structures of two- and three-dimensional polymeric complexes assembled by metal pseudohalides and 4-aminobenzoic acid via hydrogen bonds and covalent bonds

Four polymeric complexes [M(SCN)₂(4-abaH)₂]_n [M=Co(II) (1) or Cd(II) (2), 4-abaH=4-aminobenzoic acid], [Zn(N₃)(4-aba)]_n (3) and [Cd(N₃)(4-aba)(H₂O)]_n (4) were prepared from the reactions of 4-abaH with M(SCN)₂ [M=Co(II) or Cd(II)] and M(N₃)₂ [M=Zn(II) or Cd(II)] at different pH values. Their crystal structures have been determined by single-crystal X-ray diffraction. Both 1 and 2 consist of one-dimensional chains [M(μ-1,3-SCN)₂(4-abaH)₂]_n, in which each pair of the lateral carboxylic groups form double hydrogen bonds to furnish infinite two-dimensional sheets. In 3, the Zn(II) atoms are bridged by μ-1,1-azide groups and μ₂-carboxylate-O,O′ groups into an infinite zigzag chain featuring six-membered (ZnNZnOCO)_n rings, which are further connected by the 4-aba-N,O,O′ groups to generate a two-dimensional network. In 4, however, adjacent Cd(II) atoms are bridged by μ-1,1,3-azide groups to form an infinite chain with both four-membered Cd₂(μ-1,1-N₃)₂ and eight-membered Cd₂(μ-1,3-N₃)₂ rings. These chains are further connected by the 4-aba-N,O groups to generate a three-dimensional brickwall-like network. The results show significant effect of pH on the formation of the network structures.     

Zinc complexes of a new N3O ligand and their biomimetic reactions

The new N₃O ligand 2-(pyridylmethylamino)-3-(3,5-dimethylpyrazol-1-yl)-propionic acid (L1H) was synthesized and converted to L1Zn-Cl and L1Zn-Br. These complexes are tetrameric in the solid state with bridging carboxylate functions. The reaction of deprotonated L1H with zinc nitrate or zinc perchlorate yielded the aqua complexes [L1Zn-OH₂] X with and , which crystallize as carboxylate-bridged dimers. Their deprotonation produced, in situ, the hydroxide complex L1Zn-OH, which acted as a base toward p-nitrophenol and bis(p-nitrophenyl)phosphoric acid resulting in L1Zn-ONit and L1Zn-OPO(ONit)₂. Tris(p-nitrophenyl)phosphate was cleaved hydrolytically by L1Zn-OH, releasing one p-nitrophenyl group. A kinetic investigation of this cleavage reaction under pseudo-first-order conditions has yielded second-order rate constants k″ of 0.9 s⁻¹ M⁻¹ in 50% aqueous DMSO and 4.0 s⁻¹ M⁻¹ in 75% aqueous DMSO.     

Synthesis, crystal structure and properties of novel isostructural two-dimensional lanthanide-based coordination polymers with 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylic acid

Five new isostructural two-dimensional lanthanide-based coordination polymers with the formula Ln₂(F₄BDC)₃(DEF)₂(EtOH)₂-2(DEF) (Ln = Tb, 1; Gd, 2; Eu, 3; La, 4; Nd, 5; F₄BDC²⁻ = 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylate ligands; DEF = N,N′-diethylformamide), have been synthesized by reaction of Ln(NO₃)₃ and F₄BDC in a DEF/EtOH solvent mixture. The compounds were characterized by single-crystal and powder X-ray diffraction. In all cases, the metal ion is coordinated by nine oxygen atoms from two bidentate μ₂-F₄BDC²⁻ ligands, two bridging μ₂-F₄BDC²⁻ ligands, one μ₃-F₄BDC²⁻ ligand, one DEF molecule and one EtOH molecule forming a tri-capped trigonal prism. The Ln(1) metal ion is linked to an adjacent Ln(1) metal ion through the oxygen atoms of two bridging μ₂-F₄BDC²⁻ ligands and two μ₃-F₄BDC²⁻ bridging ligands to form a Ln₂O₁₈ dimer. The Ln₂O₁₈ polyhedra building units are linked to each other through four F₄BDC²⁻ ligands to form 2D sheets that are held together by hydrogen bonding to form a 3D framework. Compounds 1-5 were further characterized using thermogravimetric analysis and infrared spectroscopy. Studies of the photoluminescence properties of compounds 1 and 3, as well as the catalytic activity of compounds 3-5 in the Biginelli reaction, are presented.     

Synthetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of the aminoguanizone of pyruvic acid

Copper(II) complexes of general empirical formula, CuX(Hagpa) · nH₂O and Cu(agpa) · 2H₂O (H₂agpa = aminoguanizone of pyruvic acid, X = Cl⁻, Br⁻, , CH₃COO⁻, , n = 0, 1, 1.5, 2), have been synthesized and characterized by IR, EPR spectroscopy and X-ray crystallography. The IR spectra of the complexes showed the ONN coordination of the ligand to copper(II) ion. The crystal structures of H₂agpa · H₂O and complexes [Cu(Hagpa)Br] and [Cu₂(Hagpa)₂(H₂O)₂(SO₄)] · DMSO showed an invariable conformation and coordination mode for the uninegatively charged tridentate ligand and revealed the formation of linear polymers in which bromide or sulfate anions bridge the copper(II) ions. The EPR spectra for complexes CuX(Hagpa) · nH₂O are described by spin Hamiltonian for S = 1/2, without hyperfine structure. The g-tensor is symmetrical for Cu(agpa) · 2H₂O, has tri-axial anisotropy for sulfate complexes, and exhibits axial symmetry for the other compounds investigated.     

Zinc(II) complexes based on sterically hindered hydrotris(pyrazolyl)borate ligands: Synthesis, reactivity and solid-state structures

The coordination chemistry and reactivity of zinc(II) complexes supported by monoanionic hydrotris(pyrazolyl)borate ligands substituted by 3,3,3-mesityl groups (Tp^Ms) and 3,3,5-mesityl groups (Tp^Ms∗) have been investigated. Salt metathesis of ZnCl₂, ZnEt₂, and Zn(OAc)₂ with Tl[Tp^Ms] or Tl[Tp^Ms∗] cleanly afforded the corresponding compounds Tp^MsZnCl (1), Tp^MsZnEt (2), Tp^Ms∗ZnEt (3), and Tp^MsZnOAc (5). Compound 3 slowly disproportionates in benzene solution to afford the bis(ligand) complex (κ²-Tp^Ms∗)₂Zn (4). Acetate complex 5 as well as Tp^MsZnOCOPh (6) and [Tp^Ms∗ZnOAc]₂ (7) were alternatively prepared by acidolysis of the parent ethyl complexes (2, 3) with the corresponding carboxylic acid. No reaction was observed between 2 and 3 and alcohols (ROH; R = Et, iPr, Bn), while salt metathesis reactions of ZnEt(OR) with Tl[Tp^Ms] led to 2 instead of the desired zinc-alkoxide complex. Compounds 1-7 were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy, as well as by X-ray diffraction studies for 1, 2, 4, 5 and 7. The former compounds adopt a monomeric structure in the solid state while [Tp^Ms∗ZnOAc]₂ (7) exists as an anti-syn bridged acetate dimer. Complex 4 is four-coordinated, featuring a rare bidentate coordination mode of the Tp^Ms∗ ligands. The results are rationalized in terms of the variable steric constraint around the zinc atom provided by the Tp^Ms and Tp^Ms∗ ligands.     

Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives

Two new linear and V-shaped tetradentate ligands, namely 1,4-bis(2-hexahydropyrimidyl)benzene (L) and 1,3-bis(2-hexahydropyrimidyl)benzene (L^′), and their silver(I) complexes, [Ag₂L(μ-ONO₂)](NO₃) · 2H₂O (1), [Ag₂L(μ-pn)](NO₃)₂ (2), [Ag₂L(μ-pn)](ClO₄)₂ (3) and [Ag₄L^′₂(H₂O)](NO₃)₄ · 5H₂O (4) (pn=1,3-diaminopropane) have been synthesized in situ and structurally characterized by single-crystal X-ray diffraction. 1 and 2 were obtained from the same reaction solution but different crystallization conditions. 1 is an one-dimensional chain featuring cuboid tetranuclear silver(I) units interconnected through monoatomic nitrate bridges. Both 2 and 3 are ribbon-like helical compounds in which each L ligand acts in a tetradentate bridging mode to interconnect four metal atoms, and each pn ligand functions in a bidentate bridging mode to link a pair of metal atoms. 4 shows a truncated square-pyramidal tetranuclear motif arose by the V-shaped L^′ ligand. Close Ag?Ag separations (2.901-2.939 Å) assisted by bis(hexahydropyrimidine) bridges were observed in 1 and 4, indicating metal-metal interactions. Photoluminescence of 1-4 has also been observed in the solid state and solution at room temperature and low temperature, respectively.     

Synthesis, structure and magnetic behavior of new 1D metal-organic coordination polymer with Fe3O core

New metal-organic coordination polymer, (Me₃NH)[Fe₃(μ₃-O)(μ-HCOO)₈]·DMF (1), was synthesized by heating of Fe(NO₃)₃·9H₂O and [NH(CH₃)₃]Cl in DMF/HCOOH solution. The single-crystal X-ray structure analysis reveals this compound has 1D anionic framework structure built from Fe₃O(μ-HCOO)₆ cluster units linked by formate bridges. Compound 1 was characterized by elemental analysis, IR and TGA. The magnetic susceptibility measurements indicate a strong antiferromagnetic exchange interaction between Fe^III ions in the cluster and intercluster magnetic interaction.     

Synthesis of trans-1,4-cyclohexanedisulfonic acid and its zinc salt - A belt-like metal-organic coordination polymer with tetrahedrally and octahedrally coordinated zinc ions

Diastereomerically pure trans-1,4-cyclohexanedisulfonic acid H₂CDS was prepared in three steps from 1,4-cyclohexanediol (cis/trans-mixture) as a new linker molecule for metal-organic coordination polymers. The crystalline zinc salt contained two molecules DMF per formular unit. Infinite polymeric belts were observed in the solid state structure of [Zn(CDS)(dmf)₂]. These flat belts were formed by connecting two chains of Zn(dmf)-CDS-polymers bearing tetrahedrally coordinated Zn²⁺ ions in one chain and octahedrally coordinated Zn²⁺ centers in the second. Thermal analysis of this polymer revealed its stability up to 400 °C, above which it decomposed cleanly under formation of crystalline ZnO.     

Two heterometal-organic coordination polymers with chelidamic acid: Syntheses, structures and optical properties

Two heterometal-organic coordination polymers with chelidamic acid ligands, [AgNd(C₇H₃NO₅)₂·3H₂O]_n (1) and 0.75H₃O·[K_0.25Nd(C₇H₃NO₅)₂·3H₂O]·1.75H₂O (2), have been synthesized and characterized by X-ray single-crystal diffraction. The crystal structure of 1 features that chelating units composed of one Nd(III) ion and two tridentate chelating chelidamic acid ligands are connected by the Ag(I) ions to form a one-dimensional chain, further linked by hydrogen bonds into a 3D network. As for 2, discrete independent molecules, made up of Nd(III) and K(I) ions and chelidamic acid ligands, are linked through the hydrogen bonds to form a 1D chain, which are further inter-linked through the complex hydrogen bonds to form a 3D network. The optical properties of 1 and 2 were investigated in terms of fluorescent spectra, which both exhibit good luminescence.     

Investigation of the MSO4 · xH2O (M = Zn, x = 7; M = Cd, x = 8/3)/methyl 2-pyridyl ketone oxime reaction system: A novel Cd(II) coordination polymer versus mononuclear and dinuclear Zn(II) complexes

The reactions of methyl 2-pyridyl ketone oxime, (py)C(Me)NOH, with MSO₄ · xH₂O (M = Zn, x = 7; M = Cd, x = 8/3), in the absence of an external base, have been investigated. The synthetic study has led to the two new complexes [Zn(SO₄){(py)C(Me)NOH}(H₂O)₃] · H₂O (1 · H₂O) and [Zn₂(SO₄)₂{(py)C(Me)NOH}₄] · (py)C(Me)NOH [2 · (py)C(Me)NOH], and the coordination polymer [Cd(SO₄){(py)C(Me)NOH}(H₂O)]_n · [Cd(SO₄){(py)C(Me)NOH}(H₂O)₂]_n (3). In the three complexes the organic ligand chelates through its nitrogen atoms. The sulfate anion in 1 · H₂O is monodentate; the complex molecule is the mer isomer considering the positions of the aqua ligands. The Zn^II centers in 2 · (py)C(Me)NOH are bridged by two syn, anti η¹:η¹:μ₂ ligands; each metal ion has the cis-cis-trans disposition of the coordinated sulfate oxygen, pyridyl nitrogen and oxime nitrogens, respectively. The molecular structure of 3 is unique consisting of two different linear and ladder - type chains. π-π stacking interactions and/or hydrogen bonds lead to the formation of interesting supramolecular architectures in the three complexes. The thermal decomposition of complex 3 has been studied. Characteristic vibrational (IR, Raman) bands are discussed in terms of the nature of bonding and the structures of the three complexes.     

Syntheses, thermal analyses, crystal structures and antimicrobial properties of silver(I)-saccharinate complexes with diverse diamine ligands

Five new silver(I)-saccharinate complexes [Ag₂(sac)₂(tmen)₂] (1), [Ag₂(sac)₂(deten)₂] (2), [Ag₂(sac)₂(dmen)₂] (3), [Ag(sac)(N,N-eten)] (4), and [Ag(sac)(dmpen)]_n (5); (sac = saccharinate, tmen = N,N,N′,N′-tetramethylethylenediamine, deten = N,N′-diethylethylenediamine, dmen = N,N′-dimethylethylenediamine, N,N-eten = N,N-diethylethylenediamine and dmpen = 1,3-diamino-2,2-dimethylpropan) have been synthesized and characterized by elemental analyses, IR, thermal analyses, single crystal X-ray diffraction and antimicrobial activities. The crystallographic analyses show that all the complexes crystallize in monoclinic space group P2₁/c. In 1, the sac ligand acts as a bridge to connect the silver centres through its imino N and carbonyl O atoms forming an eight-membered bimetallic ring in a chair conformation. Complex 2 has also a dimeric structure in which the monomeric [Ag(sac)(deten)] units are linked by Ag?Ag interactions. In 3, saccharinate ligand acts as a bridging bidentate ligand between two silver(I) centres through sulfonyl group and imino N atom, forming an alternating polymeric chain through the direction [0 1 0]. In 4, the inter-molecular N-H?O hydrogen bonds form one-dimensional polymeric chains through the a axis, and these linear chains are inter-connected to each other by N-H?O hydrogen bonds, which produce a chain of edge-fused and rings along [1 0 0]. Complex 5 is a coordination polymer in which the monomeric [Ag(dmpen)(sac)]_n units are linked by Ag?Ag interactions, and the dmpen ligand acts as a bridge between the silver(I) ions, forming a two-dimensional network parallel to the (1 0 0) plane.     

Synthesis, crystal structures, and fluorescence properties of six complexes with thiophene derivative carboxylic acid ligand

The crystallization of 2,3-dihydro-thieno[3,4-b][1,4] dioxine-5,7-dicarboxylic acid (H₂tddc) with divalent transitional metal (Co, Ni, Zn, Cd) or with tervalent lanthanide metal (Sm) and with mixed ligand 4,4′-bipyridine (4,4′-bipy) or 1,10-phenanthroline (1,10-phen) formed six new complexes: [Co(C₈H₄O₆S) · 3H₂O] (1), [Co(C₈H₄O₆)(1,10-phen)(H₂O)] · H₂O (2), [Ni(C₈H₄O₆S)(4,4′-bipy)(H₂O)] · 3H₂O (3) [Sm(C₈H₄O₆S)(NO₃)(H₂O)₄] · 2H₂O (4), [Zn(C₈H₄O₆S)(H₂O)₃] (5), and [Cd₂(C₈H₄O₆S)₂(4,4′-bipy)₂] (6). The structures of these six crystals have been characterized by single-crystal X-ray diffraction analyses, which revealed that complexes 1, 4, 5 are all one-dimensional chain structures and they self-assemble into three-dimensional super-molecules via the hydrogen bond interactions and π-π stacking interactions, 2 is also a one-dimensional chain structure but still self-assembles into one-dimensional double-chains, the complex 3 has two-dimensional undulating parallelogram grid structure extended along the bc-plane, the crystal of 6 is a 3D threefold interpenetration topology framework with 4⁶6³8 nodes. The photoluminescent properties of the H₂tddc ligand and the six compounds have been measured in the solid state at room temperature. Free ligand has no luminescence, while its complexes 1, 4, and 6 all exhibit intense photoluminescence which implies that these complexes may be excellent candidates for potential photoactive materials.