109Ag NMR Research Articles

Synthesis and characterization of polymeric, anionic thiosalicylato-Ag(I) complexes with antimicrobial activities

Thiosalicylic acid ligand (H 2TSA = o-HS(C 6H 4)COOH) forms two types of anionic light- and thermally stable Ag(I) complexes with remarkable antimicrobial activities for bacteria, yeast, and mold; one is a yellow, water-soluble complex 1 and the other an orange, water-insoluble complex 2, either of which can be converted to the other, and both of which do not crystallize. Both are complexes with composition of metal: TSA 2− ligand = 1:1. The complex 2 is probably polymeric, whereas the complex 1 is an oligomer with a formula of {Na[Ag(TSA 2−)·H 2O]} n(n = 12 − 14; MW = 3600 − 4200). Both complexes have been characterized with complete elemental analyses, TG/DTA, FT-IR, and ESCA spectra in the solid state, and complex 1 as well as with molecular weight measurement in aqueous solution, and with 109Ag and 2D NMR( 1H- 1H COSY, 1H- 13C COSY, and HMBC) measurements in aqueous solution.

Effect of particle size upon catalytic and electronic properties of supported Ag catalysts: combined catalytic, 109Ag NMR and quantum chemistry studies

The rate of ethylene epoxidation over Ag Al 2O 3 supported catalysts demonstrates the drastic increase at a mean size of Ag particles about 400–500 Å. The integral intensity of the 109Ag NMR line from Ag metal particles of the same catalysts increases in the same range of particle sizes. This is due to the large line broadening of the signal from the Ag particles of which the sizes are less than 400–500 Å. The self-consistent calculations of the electronic structure of semi-infinite Ag(111) crystal show the large deviation of the local density of electronic states and 109Ag NMR Knight shifts for the first surface layers of Ag compared with Ag bulk.

Characterization of surface active sites of catalysts with high-resolution solid-state NMR

Results obtained in studies of the surface active sites of heterogeneous catalysts by use of high-resolution solid-state NMR are presented. The 1H NMR MAS (magic angle spinning) data on chemical shifts of surface OH groups and their interaction with the supported catalytically active complexes are discussed. The relation between the 1H chemical shift values of OH groups, on the one hand, and characteristics of their acid strength, such as the proton affinity PA OH of the acid residue formed on heterolytic dissociation of the OH groups, on the other hand, is presented. Changes in the intensity of 1H NMR lines for OH groups of commonly used supports (Al 2O 3, TiO 2, SiO 2 etc.) on interaction with supported oxides suggest the selective interaction of surface OH groups with supported complexes. For the solid heteropolyacid H 3PW 12O 40 (HPA) supported on SiO 2, the binding of the HPA molecule with the SiO 2 surface is most probably multicentred and results in the formation of supported species with different proton structures. Studies of 1H NMR MAS spectra of zirconium hydrides supported on SiO 2 have revealed the formation of four types of zirconium hydride complex. Solid-state high-resolution 1H NMR spectra of H 2S adsorbed on Al 2O 3 modified with KOH, K 2CO 3 and HF and on zeolites NaX, NaY and H-ZSM indicate dissociative adsorption of H 2S which occurs on the coordinatively unsaturated aluminium sites and Na + cations in zeolite cavities. The 1H and 13C NMR spectra indicate that adsorbed CH 3OH reacts more readily with SH − species than with H 2S adsorbed in the molecular form. Also presented are results of studies on Lewis acid sites in Al 2O 3, and zeolites Y and ZSM-5 using the NMR ( 1H, 13C and 15N) of weak adsorbed bases. The formation of Lewis acid sites in HY zeolites during their hydrothermal treatment has been studied by 15N NMR of adsorbed N 2O. The strongest Lewis sites are the isolated or weakly associated extralattice Al atoms. The 1H, 13C and 15N NMR chemical shifts of CH 4, N 2 and N 2O molecules, as well as 1H and 15N relaxation rates of CH 4 and N 2O adsorbed on a series of HY and H-ZSM zeolites, SiO 2 and Al 2O 3, containing controlled amounts of iron impurities, show that unlike SiO 2, γ-Al 2O 3 and HY zeolites, the H-ZSM-5 zeolites have strong electron-accepting sites formed by Fe 3+ and probably Al 3+ cations. The possible structure of these sites and the geometry of complexes formed during N 2O and CH 4 adsorption are discussed. In the final section the results obtained with 109Ag NMR of supported silver catalysts are presented. The potential of 109Ag NMR for studying catalysts of this type is discussed.

Preparation, X-ray structure and solution behavior of [Ag(9-EtGH- N7) 2]NO 3·H 2O (9-EtGH=9-ethylguanine)

The preparation and X-ray structure of [Ag(9-EtGH- N7) 2]NO 3·H 2O(9-EtGH=neutral 9-ethylguanine) is reported. The compound crystallizes in the triclinic system, space group P 1 with a=7.063(6), b=7.153(3), c=11.306(10) Å, α=83.36(6), β=76.66(7), γ=81.44(6)°. The cation is centrosymmetric with Ag(I) coordinated via two N7 positions and AgN7 bond lengths of 2.11(1) Å. Applying 109Ag NMR spectroscopy, complex formation constants for both the 1:1 complex (log β 1=0.6) and the title compound (log β 2=1.6) in Me 2SO have been determined.

Decomposition and phase separation of AgI-doped silver borate glasses

Glasses of composition (AgI) x (Ag 2OB 2O 3) 1− x (0.6<x<0.78) have been studied with 109Ag NMR and differential scanning calorimetry. By progressively increasing the annealing temperature, in all our fast quenched glasses we observe separation of crystalline silver iodide followed by decomposition of Ag 2O of the borate network. In most samples, this network crystallizes, and this causes the disappearance or weakening of the jump of heat capacity at the glass transition. On the other hand, in the x=0.75 glass, moderate amounts of AgI have been crystallized and two distinct vitreous phases have been observed. The complex process of formation and growth of the crystalline AgI domain is discussed in detail for the x=0.78 sample.

Solid-state silver-109 NMR characterization of silver dispersed on oxide supports

Magic angle spinning {sup 109}Ag solid-state NMR spectroscopy, transmission electron microscopy, X-ray diffraction, and gas adsorption measurements were used to characterize Ag particles supported on SiO{sub 2}, {eta}-Al{sub 2}O{sub 3}, and zeolite A. The samples were prepared either by a standard incipient wetness technique or by ion exchange followed by drying and reduction in H{sub 2}. {sup 109}Ag NMR spectroscopy was used to follow the state of the silver throughout the preparation process. {sup 109}Ag spectra were obtained for metallic Ag and for pure powder samples of AgNO{sub 3} and AgCl as well as for Ag{sup +} in solution; however, no resonances were observed for powder samples of Ag{sub 2}O and Ag{sub 2}O{sub 2}. Prior to drying, chemical shifts were found to be close to those of aqueous AgNO{sub 3} solutions ({approximately}O ppm), and after drying at 373 K, the chemical shift moved upfield to approach that of bulk AgNO{sub 3}. After reduction, single Knight-shifted metallic resonance at +5252{plus_minus} 10 ppm was observed for all samples which contained Ag particles larger than 50 nm in diameter. Low-loading, well-dispersed samples with smaller Ag particles yielded no observable {sup 109}Ag resonance. It is proposed that the absence of an observable {sup 109}Agmore » signal in the latter samples is due to a surface boundary effect on conduction electrons, common to other metal conductors, which broadens the signal. The adsorption of O{sub 2}, Cl{sub 2}, and HCl on the surface of the large Ag crystallites had no effect on the {sup 109}Ag spectrum. 33 refs., 10 figs., 2 tabs.« less

Solvent Self Diffusion Coefficients and 109Ag NMR Chemical Shifts in Silver Nitrate/Acetonitrile/Water Mixtures – Correlation with Macroscopic Transport Properties –

AbstractWe used the 1H NMR spin echo technique to determine the self diffusion coefficients of acetonitrile and of water in acetonitrile/water/silver nitrate mixtures. Both diffusion coefficients decrease strongly with increasing salt concentration. By comparison with earlier determined electric conductivity and viscosity data we find, that the ratio of molar conductivity and water self diffusion coefficient is constant, as well as the product of the viscosity and the acetonitrile self diffusion coefficient. The 109Ag NMR chemical shifts in these mixtures show, that silver ions are only solvated by acetonitrile.

Tetrahedral, chelated, silver(I) diphosphine complexes. Rapid measurements of chemical shifts and couplings by two‐dimensional 31P–{109Ag} NMR spectroscopy

AbstractThe 109Ag NMR spectrum of [Ag(Ph2PCHCHPPh2)2]NO3, a complex with antimicrobial and antitumour activity, was obtained using a retro‐INEPT two‐dimensional 31P–{109Ag} pulse sequence. This allowed the measurement of the 31P and 109Ag chemical shifts and the 1J(109Ag,31P) coupling constant in a single 2 h experiment and offered a considerable signal‐to‐noise gain compared with 109Ag–{31P} INEPT measurements.

(AgI)x(Ag2S·GeS2)1−x glasses studied by 109Ag NMR

The 109 Ag spin-spin and spin-lattice relaxation times for x =0.375 and x =0.5 have been measured in order to elucidate the Ag diffusion dynamics. The results are consistent with the fact that the conductivity rises with increasing x and that the GeS 2 glasses are better conductors than the corresponding B 2 O 3 glasses. Although the spin-lattice relaxation cannot be explained by the simple BPP formula or a Cole-Davidson distribution of correlation times, the data allow to estimate the number of mobile Ag ions. On the NMR time scale all ions are mobile provi---one assumes that the Ag ions “hop” from one iodine ion to the other.

109Ag NMR investigations of the superionic glasses ( AgI) x·( Ag2O·2 B2O3) 1− x

The first measurements of the 109Ag NMR relaxation times and linewidths and of the self-diffusion coefficient in ( AgI) x ·( Ag 2 O·2 B 2 O 3) 1− x are reported. The initial findings indicate that at lower temperatures (which decreases with increasing x) two distinct Ag + populations, mobile and static, can be detected. At high temperatures all cations appear to be mobile. For the x=0.65 sample, the diffusion measurements give an activation energy of 0.36±0.11 eV. The Ag local motions as probed by relaxation and linewidth measurements are associated with activation energies of about 0.10 eV.

Correlation between metal NMR physical quantities and structures of metal complexes. I. 109Ag NMR spectroscopy of aqueous silver ions coordinated with nitroxide radical

Experimental 109Ag NMR and theoretical MO methods have been used to investigate the electronic structure of silver complexes in aqueous solution. 109Ag spectra of ionic silver solutions (⩽1.0 M) can be obtained with a short repetition time (2–3 s) when 0.020 M 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl is added as a doping agent. By consideration of multiple equilibria, 109Ag chemical shifts of silver complexes in aqueous solution were found to cover a range of 0 to 1300 ppm, relative to 1.0 M AgNO 3. Tetrahedral silver complexes were at lowest field with linear silver complexes more shielded and hydrated silver ion at highest field. Our study suggests a correlation between 109Ag chemical shielding and the structure of silver complexes in aqueous solution. An ab initio SCF MO method using a STO-3G basis set is used to clarify the nature of the ligand-silver interaction and to interprete the observed 109Ag chemical shifts. The results indicate that electron density transfers from the lone pair of the ligand to vacant 5s and 5p orbitals on silver. Also back donation to ligand produces a hole in the 4d orbitals coincident with the bonding axes of silver complexes. The 109Ag chemical shieldings are found to be explained by the paramagnetic term, which depends upon p electrons and d holes on the Ag atom according to qualitative perturbation theory.

Dinuclear silver(I) and copper(I) complexes with neutral N 2S 2 donor ligands and their reactivities towards CO. Structures in solution ( 1H and INEPT 109Ag NMR) and in the solid (X-ray) of [Ag 2{μ-( R)( S)-1,2-(thiophene-2–CHN) 2cyclohexane} 2](O 3SCF 3) 2

The 1/1 reactions of the neutral N 2S 2 donor system ( R)( S)-1,2-(5-R–thiophene-2-CHN) 2–cyclohexane (R = H, 1a or Me, 1b) with [M(O 3SCF 3)] [M = Ag(I) or Cu(I)] yielded ionic complexes, consisting of a dinuclear [M 2( 1) 2] 2+ dication and O 3SCF 3 − monoanions. An X-ray crystallographic study characterized the molecular structure of [Ag 2–( 1a) 2](O 3SCF 3) 2, in the monoclinic unit cell, space group P2 1/ n, with Z = 4; a = 17.26(1), b = 15.08(2), c = 19.960(17) Å, β = 106.15(4)°, V = 4991 Å 3. The structure was refined to R is 0.0704. The two N 2S 2 ligands coor- dinate to the silver(I) centres in a bridging di- bidentate manner with short AgN(imine) [ e.g. Ag(1)N(2), 2.152(10); Ag(1)N(7), 2.162(9); Ag(2)N(3), 2.153(10); Ag(2)N(6), 2.158(10) Å] and long AgS(thiophene) distances [Ag(1)S(1), 2.961(4); Ag(1)S(8), 2.938(4); Ag(2)S(4), 2.928(4); Ag(2)S(5), 2.995(5) Å]. The Ag(1) Ag(I) separation is 2.909(1) Å. In solution the coordination properties of the N 2S 2 ligands to silver(I) and copper(I) have been studied by 1H and INEPT 109Ag NMR spectroscopy. The 1H NMR data revealed, by the presence of two thiophene–imine 1H patterns at 190 K, that at this temperature i) the structural features found for [Ag 2( 1a) 2] 2+ in the solid are retained in solution and ii) the silver(I) and copper(I) complexes have similar structures in solution. Furthermore, the presence of 3J( 1H 107,109Ag) on the imine-H resonances of the silver(I) complexes indicates that at 190 K intermolecular exchange processes are slow on the NMR time scale. From the difference in δ 109Ag of the [Ag 2( 1) 2](O 3SCF 3) 2 complexes, R = H (δ + 678) or Me (δ + 659), it was concluded that weak thiopheneSAg(I) interactions are present, and stabilize the formation of the [M 2( 1) 2] 2+ dications. However, in the reversible reactions of [Cu 2( 1) 2](O 3SCF 3) 2 with carbon monoxide the thiopheneSCu(I) bonds dissociate and neutral complexes are formed having a [{CuCO(O 3SCF 3)} 2{μ−1} 2] type of structure. In these complexes both the carbon monoxide and OSO 2CF 3 groups are terminally coordinated to Cu(I) (R = H, ν(CO), 2089 cm −1; R = Me, ν(CO) = 2087 cm −1 in CH 2Cl 2).

Silver(I) and copper(I) bis(pyridine-2-carbaldehyde-imine) triflate complexes studied in solution by 1H, 1H-{ 109Ag}, INEPT 15N and INEPT 109Ag NMR

The reactions of the neutral pyridine-imine, 6-R-py-2-CH=N-R′ (NN′), donor ligands with [M(O 3SCF 3)] [M = Ag(I) or Cu(I)] yield ionic complexes, consisting of a [M(NN′) 2] + cation and a O 3SCF 3 - anion. 1H NMR studies of the complexes which contain the prochiral substituent (R′) i-Pr or the chiral (S)-CHMePh show that in the slow exchange limit the metal IB centres have tetrahedral geometries as a result of chelate bonding of the pyridine-imine ligands. The metal IB centres have either Δ or Λ configurations. The complexes with R′ is (S)-CHMePh exist in solution in two diastereomeric forms, i.e. Δ(S)(S) and Λ(S)(S), the most abundant of which (according to 1H NMR spectra) is the Λ(S)(S) diastereomer. The (diastereomeric) selectivity is higher for the silver(I) complexes (Δ(S)(S)/Δ(S)(S) for R = H > 99/1; R = Me, 95/5) than for the corresponding copper(I) complexes (Λ(S)(S)Δ(S)(S) for R = H, 85/15; R = Me, 75/25). An INEPT 109 Ag NMR study, which was performed for the silver(I) complex with R is Me and R′ is (S)-CHMePh shows a large chemical shift difference (24 ppm) between the signals arising from the Ag(I) centres in the two diastereoisomers. Temperature-dependent 1H NMR experiments of the complexes with R′ is i-Pr show that fluxional processes occur. In the case of the silver(I) complex with R is Me and R′ is i-Pr it was established by 1H and INEPT 15N NMR that both an intramolecular process involving inversion of configuration (Δ ⇄ Λ) at the metal centre and a slower intermolecular ligand exchange process are taking place. It appeared that the rates of these processes depend on the bulkiness of the 6-pyridine as well as the imine substituents, R and R′. Moreover, the copper(I) complexes are more stable than the corresponding silver(I) complexes. Possible mechanisms for the observed exchange processes are discussed.

Application of INEPT 109Ag and 15N NMR Spectroscopy for the study of metal-ligand interactions of silver analogues of copper(I) model compounds

Because of the presence of copper (in its reduced state) at active sites in protein it has become very ▪ important to study copper(I) model complexes by spectroscopic techniques. We now report that if copper(I) in model complexes can be substituted by silver(I) with retention of the structural features then 107Ag or 109Ag NMR spectroscopy (natural abundances 50% I = 1 2 ) using the recently developed polarization transfer sequence INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) [1] provides an excellent tool for studying the metal IB-ligand interaction 1H NMR studies show that the analogous copper(I) and silver(I) complexes of potentially quadridentate N 4 ( R)( S)-1,2-(6-R-pyridine-2-CHN) 2-cyclohexane (R = H or Me) as well as the N 2S 2 donor ligand ( R)( S)-1,2-(5-R-thiophene-2-CHN) 2-cyclohexane (R = H or Me) have similar structures (confirmed by X-ray studies [2]). However, study of the direct coordination sphere and copper(I)-ligand interactions in these model complexes by Cu NMR is hampered by the large quadropole moments of both 63Cu and 65Cu (natural abudances 70 and 30% respectively, I = 3 2 ). We have measured directly 109Ag NMR (INEPT) spectra with large enhancements in signal to noise and enormous experimental time saving (a factor 400–500) as compared to the conventional methods (see Fig. 1) [3]. the influence of the nature of the hetero-atoms coordinating the metal centre is directly reflected in the chemical shift differences of the 109Ag resonances. It is shown that for silver(I) coordination complexes information about the ligand-to-metal interaction can be obtained by using not only direct 109Ag NMR, but also INEPT 15N NMR spectroscopy. In particular the 15N NMR (INEPT) spectra of the silver(I) complexes [M 2(N 4) 2] 2+ 2O 3SCF − 3 show that the structure of these complexes as found in the solid by X-ray methods, in which each metal ion has a distorted tetrahedral coordination geometry of four N-atoms, is fully retained in solution. From different 1J( 15N 107,109Ag) coupling constants the relative bond strengths of the various AgN interactions can be deduced. Where Cu I can be substituted by Ag I either in coordination (model) complexes or biological systems (bovine superoxide dismutase [4]) INEPT 109Ag NMR spectroscopy has potential as a novel technique for the study of the coordinating properties of the metal centres.

Structures and reactivities of copper(I) and silver(I) complexes of potentially quadridentate N 4 and N 2S 2 donor ligands.

In designing model complexes for the activities sites in copper proteins it is important to know the influence of the different hetero-atoms and conformational changes of the carbon skeleton on the chemical and physical properties of the metal centre. We have investigated the structure properties of copper(I) and silver(I) complexes with potentially quadridentate N 4 and N 2S 2 donor ligand system, schematically represented in Fig. 1, which have the connecting ( R)( S)−1,2-diiminocyclohexane group in common From the reaction of the N 4 donor ligand with M(O 3SCF 3) (M = Cu I or Ag I) we obtained dimeric ▪ ▪ [M 2(N 4) 2] 2+ 2O 3SCF − 3 complexes. The X-ray structure of the silver(I) complex showed that each ligand acts in a di-bidentate manner bridging the two metal centre (see Fig. 2). The silver ions have distorted tetrahedral geometries with each Ag I centre taking part in two short AgN (2.25 Å) and two long AgN (2.43 Å) interactions. The NAgN bond angle between the two short AgN bonds is circa 150°[1]. The copper(I) and silver(I) complexes are very stable and do not react further either with excess N 4 ligand or with H 2O, O 2 and CO. However, detailed 1H studies have shown that inter- and intramolecular exchange ( e.g. metal-ion or ligand exchange) occurs. These will be discussed. In contrast to these result reactions of the N 2S 2 ligand system with M(O 3SCF 3) (M = Cu I or Ag I) give rise to two different types of complexes, i.e. a dimeric [M 2(N 2S 2) 2] 2+ 2O 3SCF − 3 and a monomeric [M(N 2S 2) 2] + O 3SCF − 3 complex. According to IH and 109Ag NMR data the dimeric complex has a structure similar to that found for the [M 2(N 4) 2] 2+ 2O 3SCF 3− complex. However, in the [M 2(N 2S 2) 2] 2+ dication the imine-N atoms of the N 2S 2 ligands have strong intersections with the metal centres, while the thiophene-S atoms coordinate only weakly with the metal-IB centre. This coordination behaviour is reflected by the reactivity of the copper(I) complex, which reacts rapidly with CO(ν CO = 2092cm −1. An X-ray study is underway. The X-ray structures of the mononuclear [M(N 2S 2) 2] + O 3SCF − 3 complexes have been resolved for M = Cu I ▪ and M = Ag I to establish the exact molecular conformations and to test the validity of the assumption that copper(I) can be replaced by silver(I) with retention of the structural features [2]. As a result of the constraint of the N 2S 2 system, each ligand is primarily bonded to the metal centre (M = Cu or Ag) by one imine-N atom [N(1) and N(3)] with the remaining three hetero-atoms being held in close proximity to the metal centre (see Fig. 3: M = Cu). These complexes do not react with H 2O, O 2 and CO.

109Ag NMR SPECTRA OF AQUEOUS SILVER IONS COORDINATED WITH NITROXIDE RADICAL. SILVER–TANOL COMPLEX AND TANOL AS A DOPING AGENT

Abstract The effects of TANOL radical have been examined on chemical shifts and relaxation rates of 109Ag nmr in aqueous solution of silver salts. The silver ion in aqueous solution is found to coordinate with TANOL radical. A small amount of TANOL is added as a doping agent(0.020M), since 109Ag signals are obtained for (1.0M) silver ion within 30 minutes. The 109Ag chemical shifts of silver salt in aqueous solutions were found within the range of 0 to −1000 ppm relative to that of 1.0M AgN3.

Magnetic Susceptibility, NMR and Thermoelectric Power of Dilute Ag-Gd Alloys

Magnetic susceptibiliy, NMR and thermoelectric power measurements on dilute Ag-Gd alloys are done in temperature regions of 2 K–300 K, 4.2 K–300 K and 2 K–35 K, respectively. The effective J s - f value is derived from the impurity contribution to the 109 Ag NMR line widths as | J s - f |=0.28±0.3 eV. This value is consistent with that from the specific heat experiment, but considerably larger than that from magnetoresistance. Temperature dependence of the thermoelectric power is nearly independent of concentration and no anomalous peak is observed down to 2 K.

109Ag NMR in Dilute Ag-Gd Alloys

¹⁰⁹Ag NMR in Dilute Ag-Gd Alloys

Direct Evidence for Magnetic Domains in Silver

Pulsed NMR studies1 of 109Ag nuclei in a single-crystal specimen of Ag metal at helium temperatures in an applied field of 90 kOe reveal the presence of magnetic domains due to the de Haas-van Alphen magnetization. The H-A domains give rise to a measurable splitting of the 109Ag NMR line which appears and disappears with the H-A periodicity and has a magnitude slightly smaller than the H-A period (∼16.7 G with H0∥[100]) as expected. This effect is absent at 4.2°K and, on cooling down, sets in at about 2.2°K. Our results demonstrate the remarkable property, predicted by theory,2 that in the domain region of the H-A cycle the magnetic induction inside a planar specimen is independent of the applied field. The sharply resolved NMR lines give evidence for a large ratio of domain size to wall thickness and confirm the previously calculated positive wall energy.3

Nuclear Magnetic Resonance in Palladium-Silver Alloys

The 109Ag NMR has been studied in a series of Pd1−xAgx alloys by spin-echo techniques in external fields near 55 kOe and at temperatures of 1°–4°K. Knight shifts (K), spin-lattice (T1), and spin-spin (T2) relaxation times were determined for 12 compositions in the range 0.025≤x≤1. The shifts are negative for x≤0.35. From the observed lineshape in the x = 0.025 alloy (K = −1.41%) it is estimated that K = −1.46% in the limit of infinite dilution. After adjustment for an estimated direct contact shift of +0.34%, this value yields a hyperfine field of −140(±10) kOe/μB of palladium d-spin magnetization, which presumably arises from spin polarization of the s conduction electrons by the palladium host. This process is found to be ineffective as a spin-lattice relaxation mechanism. The observed relaxation times T1T increase gradually from a value of 9.6(±0.5) sec·°K for pure silver to a broad maximum of 26(±3) sec·°K near x = 0.3 and remain nearly constant at lower concentrations [T1T = 22(±4) sec·°K for x = 0.025]. The variation of (T1T)−1/2 with composition is qualitatively consistent with the expected variation of the s electron density of states at the Fermi level. The 105Pd spin-lattice relaxation times in palladium metal have been remeasured with the result T1T = 0.7(±0.2) sec·°K.