Post-transition Metal Ions Research Articles

Inhibition of metal ion complexation by an N2O2-donor macrocycle by incorporation of an intramolecularly hydrogen-bonding pendant phenolic group

The synthesis and X-ray structure of a new pendant-arm derivative of a parent 14-membered N2O2-donor macrocycle bearing an N-substituted 6-methylene-2,4-dimethylphenol group is presented. A single crystal X-ray study shows a strong intramolecular hydrogen-bond between the pendant phenol proton and the tertiary nitrogen of the macrocyclic ring, which may inhibit its ability to bind with selected transition and post-transition metal ions.

Synthesis, characterization, fluorescence and computational studies of new Cu2+, Ni2+ and Hg2+ complexes with emissive thienylbenzoxazolyl-alanine ligands

The interaction of four fluorescent compounds containing thiophene and benzoxazole moieties combined with an alanine residue with alkaline, alkaline-earth, transition and post-transition metal ions was explored. The highly fluorescent heterocyclic alanine derivatives are strongly quenched in the solid state after complexation with the paramagnetic metal ions Cu2+ and Ni2+, and with the diamagnetic Hg2+. Absorption and steady-state fluorescence titrations reveal a selective interaction with Cu2+, Ni2+ and Hg2+. In all cases the formation of mononuclear or dinuclear metal complexes in solid state and in solution are postulated. DFT calculations on the mercury(II) complexes confirm the formation of dinuclear species. Our results suggest that one metal ion is coordinated by the chelate group formed by the amine and the protonated carboxylic groups present in the amino acid residue while a second metal ion is directly linked to the chromophore. As parent compound, L4 shows no interaction with Cu2+ and Ni2+ salts. However, the interaction with Hg2+ induces a strong quenching and a red shift of the fluorescence emission.

Synthesis of metal complexes with a novel ethyldioxolane pendant-arm hexaazamacrocyclic ligand

The coordination capability of a pendant-arm azamacrocyclic ligand L with four ethyldioxolane pendant groups towards transition, post-transition and lanthanide metal ions was achieved. In all cases, complexes with a 2:1 metal:ligand molar ratio were obtained. The complexes were characterized by elemental analysis, MS-FAB, IR, conductivity measurements, 1H and 13C NMR spectroscopy. Crystal structures of [CoL][CoBr 0.5(NO 3) 3.5] and [(H 2O)H 2L][Nd(NO 3) 4(H 2O) 3]NO 3·3.5H 2O have been determined. The [CoL] 2+ cation contains the Co(II) ion endomacrocyclicly coordinated in a distorted octahedral geometry with a N 6 core. The Nd(III) complex presents a mononuclear exomacrocyclic structure with an 11 coordination environment. π,π-Stacking interactions have been observed between the pyridine rings of the protonated ligand [(H 2O)H 2L] 2+, and the [Nd(NO 3) 4(H 2O) 3] 2− anion.

Spectrophotometric study of complexation of dibenzopyridino-18-crown-6 with some transition and post-transition metal ions in DMSO solution using murexide as a metallochromic ligand

The complexation reaction of dibenzopyridino-18-crown-6 (DBPY 18C6) with Co2+, Cu2+, Zn2+, Pb2+, Cd2+, Hg2+, and Ag+ have been studied in DMSO at 25°C by the spectrophotometric method. Murexide was used as a competitive colored ligand. The stoichiometry of metal ion-murexide and metal ions with DBPY18C6 complexes were estimated by mole ratio and continuous variation methods and emphasized by the KINFIT program. The stoichiometry of all the complexes was found to be 1: 1 (metal ion/ligand). The order of stability constants for the obtained metal ion-murexide complexes (1: 1) varies in the order Cu2+ > Cd2+ > Co2+ ∼ Pb2+ > Zn2+ > Ag+ > Hg2+. This trend shows that the transition metal ions clearly obey the Irving-Williams role. For the post-transition metal ions, the ionic radius and soft-hard behavior was the major affects in varying of this order. The dibenzopyridino-18-crown-6 complexes with the used metal ions vary as Ag+ > Pb2+ > Cu2+ > Cd2+ > Hg2+ > Zn2+ > Co2+.

Synthesis and coordination properties of an azamacrocyclic Zn(II) chemosensor containing pendent methylnaphthyl groups

The synthesis of a polyazamacrocycle constituted by two diethylenetriamine bridges functionalized at their central nitrogen with naphth-2-ylmethyl units and interconnected through 2,6-dimethylpyridine spacers (L1) is reported. The protonation behaviour of the new macrocycle in water and in water-ethanol 70/30 v/v mixed solvent has been examined by means of pH-metric, UV-Vis and steady-state fluorescence techniques. The fluorescence emission is slightly quenched following the deprotonation of the central tertiary amines and more deeply quenched upon deprotonation of the secondary amino groups. pH-Metric titrations show that in water-ethanol 70/30 v/v L1 forms stable mononuclear complexes with the divalent transition and post-transition metal ions Mn2+, Fe2+, Co2+, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+. In the case of Cu2+, Zn2+, Hg2+ and Pb2+, formation of binuclear complexes has also been observed. Steady-state fluorescence emission studies show that while interaction with Cu2+ leads to quenching of the fluorescence emission above pH = 2, interaction with Zn2+, Cd2+, Hg2+ and Pb2+ give rise to enhancements of the fluorescence above pH ca. 5, which is particularly noticeable in the case of Zn2+.

Metal ion interaction with a novel anthracene pendant-armed fluorescent molecular probe. Synthesis, characterization, and fluorescence studies

A new scorpionate system ( L) containing an emissive anthracene pendant arm, derived of O 1, O 7-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren, has been synthesized and characterized. The sensing capability of L towards a range of metal ions has been studied. Protonation and complexation studies, using UV–Vis and fluorescent emission measurements, have been performed with alkaline and alkaline earth metal ions (M = Na(I), K(I), Li(I), Ca(II), Mg(II)), as well as transition and post-transition metal ions (M = Cr(III), Cu(II) and Zn(II), Cd(II), Hg(II) and Al(III)). An increase in the fluorescence emission (CHEF effect) was observed in methanol and in methanol/water mixtures in the presence of Cd(II) (5.0-fold), Zn(II) (4.5-fold), Cr(III) (2.0-fold) and Al(III) (1.8-fold); these results suggest a notable sensing ability of this new N 3O 4 ligand for these metals; these experiments were also performed in the presence of large amounts of alkaline and alkaline earth metal ions.

Synthesis, coordination properties, and analytical applications of mixed donor macrocycles containing the 1,10-phenanthroline sub-unit

The coordination properties towards different metal ions of a new class of mixed N/S-, and N/S/O-donor macrocycles containing the 1,10-phenanthroline sub-unit in the cyclic framework are reviewed. The conformational constraints imposed by the heteroaromatic fragment onto the aliphatic portion of the ring determine the coordination mode of these ligands which can stabilise low-valent Ni+, Pd+, Pt+, and Rh+ metal complexes. Structural and thermodynamic aspects of the coordination chemistry of these ligands are considered together with possible applications as building blocks in the synthesis of multi-centred systems, and as template in the construction of extended polyiodide networks. However, solution studies demonstrate the inability of these ligands to work as selective and specific fluorescent chemosensors for heavy transition and post-transition metal ions and the formation constants evaluated for the formation of 1:1 complexes with Pb2+, Cd2+, Hg2+, Cu2+, and Ag+ in acetonitrile are of the same order of magnitude. Nevertheless, some of these macrocyles are extremely effective to recognise Cu2+ or Ag+ over the other metal ions in transport processes, and have been successfully used as neutral ionophore in the construction of PVC-based ionselective electrodes and supported liquid membranes for analytical detection and separation, respectively, of these metal ions.

Macrocyclic ligand design: The interaction of selected transition and post-transition metal ions with a 14-membered N 2S 2-donor macrocycle

Interaction of 1,7-dithia-4,11-diazacyclotetradecane ( 1) with nickel(II), copper(II) and silver(I) yields the complexes [NiL(H 2O)(CH 3CN)](ClO 4) 2, [CuL](ClO 4) 2 and [AgL] n (ClO 4) n (L = 1). The log K values for the 1:1 complexes of cobalt(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) in 95% MeOH are reported, with the strongest complexes occurring for copper(II) and silver(I). The X-ray structure of the nickel complex shows the four donors of the macrocycle coordinated around cis positions of an octahedron, with water and acetonitrile ligands occupying the remaining cis positions (the latter are trans to the amine donors and the sulfurs occupy trans axial positions). The silver complex is distorted square pyramidal with all macrocyclic donors bound; each sulfur bridges to an adjacent silver centre such that the latter attains a S 3N 2 environment and a cationic zig-zag polymeric arrangement is generated.

Metal complexes with two tri-aza, tri-oxa pendant-armed macrocyclic ligands: Synthesis, characterization, crystal structures and fluorescence studies

Metal complexes of two new tri-aza, tri-oxa macrocycles containing ethyl acetate ( L 1 ) or carboxymethyl ( H 2 L 2 ) pendant arms with hydrated nitrate or perchlorate salts of alkaline earth, post-transition and lanthanide metal ions have been synthesized and characterized by microanalysis FAB MS, conductivity measurements, IR, UV–Vis spectroscopy and fluorescence emission studies. The synthesis and characterization of the Pb(II) complexes with the armless macrocyclic precursors L (Schiff base macrocycle) and L′ (diaminic reduced macrocycle) are also reported. The crystal structures of complexes [PbL(ClO 4)(H 2O)](ClO 4), [PbL′(ClO 4)](ClO 4) and ([Zn 2L 2(Cl)(H 2O)](ClO 4)) ∞ have been determined. In both lead(II) complexes, the metal ion is located inside the macrocyclic cavity and is coordinated by all N 3O 3 donor atoms in the complex with L′ but only by the nitrogen atoms present in the ligand in the complex with L. In both cases, the coordination sphere of the metal atom is completed with a perchlorate anion or a water molecule in the iminic complex of L. X-ray studies on the Zn(II) complex show the presence of a supramolecular structure that is consistent with a linear polymer formed alternately by an endomacrocyclic metal atom coordinated to a macrocyclic ligand and an exomacrocyclic metal ion in distorted octahedral and tetrahedral environments, respectively. UV–Vis and fluorescent emission studies were carried out on the ligands L 1 and H 2L 2 and their metal complexes, but only the luminescence spectra of the Eu(III) and Tb(III) complexes with L 1 in aqueous solution at ca. pH 7 show the characteristic visible emission of the metal. The value of the quantum yield determined for the Eu(III) complex is similar to that reported in the literature for other Eu(III) complexes.

Competitive bulk liquid membrane transport and solvent extraction of some transition and post-transition metal ions using acylthiourea ligands as ionophores

Competitive transport experiments involving metal ions from an aqueous source phase through a chloroform membrane into an aqueous receiving phase have been carried out using a series of acylthiourea ligands as the ionophore present in the organic phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), silver(I), cadmium(II) and lead(II) with the source and receiving phases being buffered at a number of different pHs. Transport selectivity was observed for silver(I) in all but one case. Selectivity for silver(I) was also observed in a series of parallel solvent extraction experiments carried out under similar source and membrane phase conditions. An X-ray diffraction study of the silver(I) complex of the N,N-dibutyl-N′-benzoylthiourea from this series is reported. There are two crystallographically independent molecules in the asymmetric unit and each molecule consists of four silver(I) ligand complex units, hence giving rise to Z = 8. In each molecule, both chelate and monodentate co-ordination modes of complexation to silver(I) are evident. Hence, each silver is co-ordinated to a sulfur and oxygen atom from one ligand and to a shared (bridging) sulfur from another ligand. Each silver atom is thus co-ordinated to three donor atoms.

A rapid identification system for metallothionein proteins using expert system

Metallothioneins (MT) are low molecular weight proteins mostly rich in cysteine residues with high metal content. Generally, MT proteins are responsible for regulating the intracellular supply of biologically essential metal ions and they protect cells from the deleterious effects of non-essential polarizable transition and post-transition metal ions. Due to their biological importance, proper characterization of MT is necessary. Here we describe a computer program (ID3 algorithm, a part of Artificial Intelligence) developed using available data for the rapid identification of MT. Tissue samples contains several low molecular weight proteins with different physical, chemical and biological characteristics. The described software solution proposes to categorize MT proteins without aromatic amino acids and high metal content. The proposed solution can be expanded to other types of proteins with specific known characteristics.

Fluorescence response of mono- and tetraazacrown derivatives of 4-aminophthalimide with and without some transition and post transition metal ions

The fluorescence response of two fluorophore–spacer–receptor systems, 1 and 2, wherein a 4-aminophthalimido moiety is linked to a monoaza- and a tetraazacrown macrocycle via a dimethylene spacer, has been explored in the absence and in the presence of various transition and post transition metal ions. Unlike the parent fluorophore, these systems are weakly fluorescent because of photoinduced electron transfer (PET) between the terminal moieties of the molecules. Of the two systems, PET is found to be more efficient in 2, which contains the tetraazacrown moiety as the receptor. Both systems display complex fluorescence decay behaviour with the average fluorescence lifetime much shorter than that of the parent fluorophore. The systems exhibit fluorescence enhancement in the presence of the metal ions, some of which are notorious quenchers of fluorescence. While the fluorescence output of 1 is rather similar with different metal ions, 2 exhibits high fluorescence enhancement with metal ions such as Zn2+, Cd2+, Pb2+, Hg2+ and Mn2+ while producing negligible enhancement with the remaining metal ions studied. This specific signaling behaviour of 2 has been rationalized taking into consideration somewhat unusual binding ability of the tetraazacrown receptor moiety.

A study of 4-(alkylamino)amino substituted 1,8-naphthalimide fluoroionophores

The fluorescence enhancement (FE) of five 4-(alkylamino)amino-1,8-naphthalimide fluoroionophores upon addition of sub-ppm concentrations of transition, post-transition, and lanthanide metal ions is investigated and the results are reported. Changes in (alkylamino)amine ligand chain length result in significantly different fluorescence enhancement behavior. 4-Diamino substituted 1,8-naphthalimides with two, three, and four carbons between amines exhibit fluorescence enhancement, while substituents of five- and six-carbon spacing between amines exhibit no fluorescence enhancement. Metal ion selectivity as measured by complexation coefficients (log β) is observed with the ethylenediamine and propylenediamine substituted compounds for Cu 2+, and metal ion selectivity for Pb 2+ is observed for the butanediamine derivative. Inhibition of photoinduced electron transfer (PET) between the distal nitrogen and the aromatic system by metal ion coordination to the distal amine is the mechanism of fluorescence enhancement for the ethylenediamine, propylenediamine, and butanediamine derivatives.

Macrocyclic ligand design. Structure–function relationships involving the interaction of pyridinyl-containing, oxygen–nitrogen donor macrocycles with selected transition and post transition metal ions on progressive N-benzylation of their secondary amines

Structure-function relationships underlying the interaction of progressively N-benzylated N(4)O(2)-donor macrocycles with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) have been probed using a range of techniques that include X-ray diffraction, DFT computations, solvent extraction, potentiometric stability constant determinations and competitive membrane transport experiments. Collectively, the results indicate that N-benzylation of the secondary amine donor groups of the parent macrocyclic ring results in an enhanced tendency towards selectivity for silver(I) relative to the other six metals investigated. The observed behaviour serves as additional exemplification of the previously proposed concept of selective 'detuning' as a mechanism for metal ion discrimination.

Metal ion recognition via 'selective detuning'. The interaction of selected transition and post-transition metal ions with a mono-N-benzylated O2N3-donor macrocycle and its xylyl-bridged ring analogue.

The interaction of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) with symmetrical mono-N-benzylated and xylyl-linked macrocyclic ligands derived from the O2N3-macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, has been investigated. The log K values for the respective 1 : 1 complexes in 95% methanol (I= 0.1; Et4NClO4, 25 degrees C) of the mono-benzylated derivative have been determined potentiometrically and the results compared with the values obtained previously for the parent (non-benzylated) ring system as well as for related di- and tri-benzylated macrocyclic species. Mono-benzylation results in slightly enhanced stability for the 1 : 1 silver(I) complex while the values for the corresponding complexes of the other six ions are in each case decreased even though the highest stability is still maintained for the 1 : 1 copper(II) complex. The log K results are in accord with a previous proposal that N-benzylation of amine-containing macrocyclic rings of the present type will normally have only a minor (positive or negative) influence on the affinity towards silver(I) while the corresponding binding strengths towards the remaining six metal ions are significantly reduced-behaviour we term 'selective detuning'. Competitive seven-metal transport experiments across a bulk chloroform membrane have been performed using both ligand systems as ionophores. In parallel to the log K results, transport selectivity for copper(II) was exhibited by both systems, with similar transport efficiencies being evident when compared on a 'per macrocyclic cavity' basis.

Synergistic effects in multicomponent electrocatalysts: the Pb-Ir-O system.

The ionic interactions were studied in aqueous solutions of Na(3)IrCl(6) + Pb(NO(3))(2) in order to develop a facilitated electrosynthesis of iridium-based catalytic surfaces. Spectroscopic studies indicated that ion pair charge-transfer complexes [IrCl(6)(3-)]-Pb(II) (K = 6 x 10(3)) and [Ir(H(2)O)Cl(5)(2-)]-Pb(II) (K = 2 x 10(3)) were formed in fresh and aged solutions, respectively. Electrochemical studies showed that interactions between the Ir(H(2)O)Cl(5)(2-) and Pb(II) species lead to synergistic lowering of the overpotential that was necessary for nucleation and growth of mixed metal oxide PbIrOx on the surface of glassy carbon electrodes. The Ir:Pb stoichiometry of the PbIrOx surface films was the same (1:1) as that of the high-temperature phase of Pb-Ir-O pyrochlore. Compared to IrOx, the PbIrOx films displayed enhanced catalytic activity toward the electrooxidation of carbohydrates. This was ascribed to synergism that involved retention of carbohydrate molecules at the Pb(II) sites of a PbIrOx film and oxidation at the adjacent Ir(IV) sites. The synergistic electroplating utilizing interactions between the partially aquated transition metal complex and posttransition metal ion represents a new synthetic route to highly homogeneous and reactive films of mixed metal oxides.

Synthesis of perchlorate metal complexes with a new tetrapyridyl pendant armed macrocyclic ligand

A new pendant-armed macrocyclic ligand, L 1, bearing four pyridyl pendant groups has been synthesized by N-alkylation of the tetraazamacrocyclic precursor L with picolyl chloride hydrochloride. Metal complexes of L 1 using hydrated perchlorate salts of transition and post-transition metal ions have been synthesized and characterized by microanalysis, MS FAB, conductivity measurements, IR, UV–Vis, 1H and 13C NMR spectroscopy and magnetic studies. When Ni(II) or Cd(II) perchlorate salts are used 1:1 metal complexes are obtained, whereas with Co(II) or Ag(I) salts the 2:1 metal:ligand complexes are obtained. Nevertheless when Cu(II) or Zn(II) salts are employed 1:1 and 2:1 complexes are obtained depending on the stoichiometry of the reaction. Crystal structures of the ligand L 1 as well as of the complexes [NiL 1](ClO 4) 2·2H 2O, [CuL 1](ClO 4) 2·2H 2O, [Cu 2L 1(CH 3CN) 2](ClO 4) 4·2CH 3CN, [ZnL 1](ClO 4) 2·4H 2O, [CdL 1](ClO 4) 2·2CH 3CN and [Ag 2L 1](ClO 4) 2·2CH 3CN have been determined. The X ray studies show the presence of two metal atoms within the cavity of the macrocyclic ligand in [Ag 2L 1](ClO 4) 2·2CH 3CN, whilst in [Cu 2L 1](ClO 4) 4·4CH 3CN the copper atoms are coordinated exocyclically to the nitrogen atoms from the pendant arms of the ligand. The crystal structures of [NiL 1](ClO 4) 2·2H 2O, [CuL 1](ClO 4) 2·2H 2O, [ZnL 1](ClO 4) 2·4H 2O and [CdL 1](ClO 4) 2·2CH 3CN show mononuclear endomacrocyclic complexes with the metal ion coordinated to six nitrogen atoms in a distorted octahedral environment.

Enhanced metal extractive behavior using dual mechanism bifunctional polymer: an effective metal chelatogen

A new class of chelating polymers using Amberlite XAD-16 (AXAD-16) modified with ( N-(3,4-dihydroxy)benzyl)-4-amino,3-hydroxynapthalene-1-sulphonic acid has been developed based on dual mechanism bifunctional polymers, for the extraction of transition and post-transition metal ions. The optimum pH conditions for the quantitative sorption of metal ions were studied. The developed method showed superior extraction qualities with high metal loading capacities of 71, 85, 182, 130 and 46 mg g −1 for Ni(II), Cd(II), Pb(II), Cu(II) and Co(II), respectively. The rate of metal ion uptake i.e. kinetics studies performed under optimum levels showed a time duration of <5 min except for Co(II) which required 20 min, for complete metal ion saturation. Desorption of metal ions were effective with 15 ml of 2 M HCl/HNO 3 prior to detection using flame atomic absorption spectrophotometer. The chelating polymer was highly ion-selective in nature even in the presence of large concentrations of alkali and alkaline earth metal ions, with a high preconcentrating ability for the metal ions of interest. The developed chelating matrix was tested on its utility with synthetic and real samples like river/sea/tap/well water samples and also with multivitamin/mineral tablets, showed R.S.D. values of <2.5% reflecting on the accuracy and reproducibility of data using the newly developed resin matrix.

Metal ion recognition. Interaction of a series of successively N-benzylated derivatives of 1,4,8,11-tetraazacyclotetradecane (cyclam) with selected transition and post-transition metal ions

The interaction of a series of N-benzylated cyclam ligand derivatives incorporating from one to four N-benzyl groups with cobalt(II), zinc(II), cadmium(II), lead(II) and silver(I) nitrates is reported; the results are compared with those obtained in a prior study involving the formation of the corresponding complexes of nickel(II) and copper(II) with this ligand series. The isolation of a selection of 1 ∶ 1 (metal ∶ ligand) complexes has been carried out and X-ray diffraction structures of five such products have been determined. In each complex the metal ion is coordinated to the N4-donor set of the cyclam ring with the latter adopting either a trans-I or a trans-V configuration; monodentate or bidentate nitrato ligands complete the respective coordination spheres. Coordination numbers range from five in a zinc(II) complex, through six in two cadmium(II) complexes, to eight in two lead(II) complexes. Competitive bulk membrane transport experiments (water/chloroform/water) have been carried out in which each of the five benzylated ligands were in turn employed as the ionophore in the chloroform phase. The respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) nitrates. The aqueous receiving phase was buffered at pH 3.0. Under these conditions, high selectivity for copper(II) was observed for each of the ionophores incorporating one or two N-benzyl groups whereas no transport for any of the seven metals present in the source phase was observed for the tribenzylated derivative. In marked contrast to the above behaviour, the tetra-N-benzyl derivative yielded sole transport selectivity for silver(I) under similar conditions. 1H NMR and 13C NMR titration experiments in CD3CN–CDCl3 confirmed the 1 ∶ 1 stoichiometry of the silver(I) tetra-N-benzylcyclam complex in this solvent mixture.

Competitive bulk membrane transport and solvent extraction of transition and post transition metal ions using mixed-donor acyclic ligands as ionophores

Competitive transport experiments involving metal ion transport from an aqueous source phase across a chloroform membrane phase into an aqueous receiving phase have been carried out using a series of open-chain mixed-donor ligands as the ionophore in the organic phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II), with the source and receiving phases being buffered at pH 4.9 and 3.0, respectively. Clear transport selectivity for silver(I) was observed in all cases. This was also observed in a series of parallel solvent extraction experiments carried out under similar source and membrane phase conditions. Stability constant data confirm that all these ligands show significant affinity for silver(I) in methanol. An X-ray diffraction study of the silver(I) complex of a tripodal NS3-donor ligand from the present series is reported. This complex occurs as two crystallographically independent molecules with both forms having a 1 ∶ 1 silver ∶ ligand ratio. The metal coordination geometry of the first form is distorted tetrahedral, with three coordination sites occupied by the three sulfur atoms of the ligand and the fourth site filled by an oxygen atom of the nitrate anion. The silver ion in the second form is five-coordinate being bound to the ligand's apical nitrogen as well as to its three sulfur donors. The remaining position is again occupied by a nitrate oxygen, with the metal coordination geometry in this case best described as distorted trigonal bipyramidal.