Cation Of Compound Research Articles

Hexachlororhenate(IV) salts of organic radical cations

The ionic salts ( p-rad) 2[ReCl 6] ( 1) and ( m-rad) 2[ReCl 6] ( 2) ( p/ m-rad = 2-(4/3- N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazol-1-oxyl-3- N-oxide) have been prepared and their crystal structures determined by single-crystal X-ray diffraction. The nitronyl nitroxide cations in compound 1 show a layered disposition, whereas the [ReCl 6] 2− units are placed between these layers. The nitronyl nitroxide cations in compound 2 adopt an hexagonal array but they do not result in layers. Bulk magnetic properties of 1 and 2 have been investigated in the temperature range 2–300 K. Both compounds show weak but significant intermolecular antiferromagnetic interactions.

A Bicyclic P–P‐Bridged 1,3,2,4‐Diphosphadiboretane Cation and an Imino(phosphinidene)borane–AlBr3 Adduct

AbstractDepending on reaction conditions the 1,3,2,4‐diphosphadiboretane 1 reacts with AlBr3 to give the unstable adduct tmp=B=P(tBu)AlBr3, 3, and/or the somewhat more stable salt [(tmpB)2(PtBu)P]+[AlBr4], 2. The X‐ray structure determination of 3 shows an almost linear NBP array with BN and BP double bonds resembling an allene type structure. NBO analysis shows the presence of BN‐ and BP‐π‐bonds. On the other hand, the cation of compound 2 has a bicyclic structure with a long P–P bond [2.349(2) Å]. The B–P bonds to the phosphonium type P2 atom [av. 1.939(5) Å] are longer than those to the tri‐coordinated P1 atom [1.889(6) Å]. NBO analysis of the model compound (H2NB)2(PMe)P+, 9, show that the P–P bond in 2 is formed from p‐orbitals.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Dinuclear copper(II) complexes of four new pyrazole-containing macrocyclic ligands are active catalysts in the oxidative coupling of 2,6-dimethylphenol

Four new macrocyclic ligands of varying ring size, [22]py4pz, [22]pr4pz, [18]py2pz and [20]py2pz, containing four or two endocyclic pyrazole groups, form dinuclear copper compounds. The single crystal X-ray structures of [Cu(pr2pz)(ClO 4) 2] ( A), [Cu 2([22]pr4pz)Cl 4](MeOH) ( B), [Cu 4([18]py2pz) 2(μ-Cl) 4Cl 2]Cl 2 ( C) and [Cu 2([18]py2pz)(CH 3CN) 4(ClO 4) 2](ClO 4) 2(CH 3CN) 1.6 ( D), show the pyrazole groups and the amine nitrogens all to be involved in the coordination of the copper(II) ions. In the mononuclear compound A the copper ion is in a distorted octahedral geometry, with the equatorial plane formed by four nitrogen donor atoms from the ligand and the axial positions occupied by two oxygen atoms from mono-coordinated perchlorate anions. In compound B each copper ion is in a distorted square pyramidal environment, with the three ligand nitrogens and a chloride atom in the equatorial plane and another chloride atom in the axial position. The cation of compound C contains four copper centers. Two bridging Cl atoms connect the two central copper atoms to form a centrosymmetric four membered ring. Two macrocyclic units are present in the cation, each containing two copper atoms bridged by a chloride atom. One copper is fivefold coordinated and the second copper is distorted octahedral. In compound D both copper(II) ions are in a distorted octahedral N 5O environment, with the equatorial plane formed by the three ligand nitrogens and a nitrogen from an acetonitrile molecule. A second acetonitrile molecule and a mono-coordinated perchlorate anion are weakly bound in the axial positions. The copper nitrate compounds of these new ligands are to some degree active catalysts in the oxidative coupling of 2,6-dimethylphenol with molecular dioxygen to poly(2,6-dimethyl-1,4-phenylene ether).

On the Incorporation of Transition Metal Atoms into Thiostannates: Synthesis, Crystal Structures and Spectroscopic Properties of [Ni(en)3]2Sn2S6, [Ni(dap)3]2Sn2S6 · 2 H2O, [Co(tren)]2Sn2S6, and [Ni(tren)]2Sn2S6

AbstractThe four new thiostannates [Ni(en)3]2Sn2S6 (1) (en = ethylenediamine), [Ni(dap)3]2Sn2S6 · 2 H2O (2) (dap = 1, 2‐diaminopropane), [Co(tren)]2Sn2S6 (3) and [Ni(tren)]2Sn2S6 (4) (tren = tris(2‐aminoethyl)amine) were prepared under solvothermal conditions. In all compounds [Sn2S6]4— anions are observed as the common structural motif. This anion is composed of two SnS4 tetrahedra sharing a common edge. In compounds 1 and 2 the transition metal cations are coordinated each by three amine ligands and therefore solvent separated complex cations as well as discrete [Sn2S6]4— anions are found. In compounds 3 and 4 the coordination around the transition metal ions cannot be completed by the organic ligands and the [Sn2S6]4— anions are connected to the transition metal cations via terminal S atoms. In both compounds the [Sn2S6]4— anion acts as a bidentate ligand connecting two transition metal cations by terminal S atoms. The Co2+ cations in compound 3 are in a fivefold environment of one tetradentate tren ligand and one S atom forming discrete[Co(tren)]2Sn2S6 units. In compound 4 the Ni2+ ions are in a sixfold environment of one tetradentate tren ligand and two S atoms of two symmetry related [Sn2S6]4— anions. This connection mode leads to formation of “zig‐zag‐like” Ni—Sn2S6 chains which are directed along the crystallographic c‐axis. The spectroscopic properties of compounds 1 to 3 were investigated using Raman spectroscopy. Differences in the spectra of 1 and 2 compared to 3 are observed which are caused by the covalent bonding between the Co2+ ions and the Sn2S64— anions in 3.

Control of Oxidation States of Transition Elements (Cr, Mn) in Nitridometalates and the Solid Solution Series Li6(Ca1‐xSrx)2[Mn2N6

AbstractThe formation of ternary nitridometalates from the elements in the case of the systems Li—Cr, V, Mn—N leads to compounds which contain the transition metals in the highest (VV, CrVI) or a comparably high (MnV) oxidation state. In the corresponding calcium and strontium systems, the transition metals show a lower oxidation state (VIII, CrIII, MnIII). Transition metals with intermediate oxidation states (CrV, MnIV) are present in the quaternary (mixed cation) compounds Li4Sr2[CrN6], Li6Ca2[MnN6], and Li6Sr2[MnN6] (R3¯(#148), a = 585.9(3) pm, c = 1908.6(4) pm, Z = 3), as well as in the solid solution series Li6(Ca1—xSrx)2[MnN6].

Quasi-intramolecular acid–base reactions in aqueous solutions of metal-complexes of basic ligands I. Generalized theoretical considerations on the deammoniation of [MLm]Xn type ammonia complexes

The theoretical investigation on the distribution of chemical species obtainable as a function of the temperature of the aqueous solutions of metal complexes containing a basic ligand, altogether with the solubility relationship of the compounds to be formed, offers a simple means of planning the preparation of various types of complexes, double and single salts of the central metal cation and onium type compounds of protonated ligand of the central ion and the anion.

Different oxidation states of copper(I, I/II, II) thiocyanate complexes containing 1,2,4-triazole as a bridging ligand: syntheses, crystal structures, and magnetic properties of 2-D polymer Cu I(admtrz)SCN, linear trinuclear [CuI2CuII(admtrz)6(SCN)2](ClO4)2, and triangular trinuclear [CuII3(admtrz)4(SCN)3(mu3-OH)(H2O)](ClO4)2.H2O (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole).

Copper thiocyanate compounds with three different oxidation states, Cu(I)(admtrz)SCN (1), [Cu(I)(2)Cu(II)(admtrz)(6)(SCN)(2)](ClO(4))(2) (2), and [Cu(II)(3)(admtrz)(4)(SCN)(3)(mu(3)-OH)(H(2)O)](ClO(4))(2).H(2)O (3), have been synthesized and characterized (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole). Compounds 1 and 3 crystallize in the space group Pbca of the orthorhombic system with eight formula units in cells of dimensions a = 8.0221(2) A, b = 32.3844(1) A, c = 13.5659(3) A, R1/wR2 = 0.0595/0.1674 for compound 1 and a = 21.501(3) A, b = 18.382(2) A, c = 21.526(2) A, R1/wR2 = 0.0638/0.1519 for compound 3. Compound 2 crystallizes in the space group C2/c of the monoclinic system with four formula units in cells of dimensions a = 18.772(4) A, b = 11.739(2) A, c = 22.838(5) A, beta = 91.11(3) degrees, R1/wR2 = 0.0482/0.1265. The layered-type structure of 1 can be regarded as constructed from the tetranuclear copper units double bridged by one of the two unique thiocyanate and admtrz ligands, which are bridged by the other unique thiocyanate ligands to form a two-dimensional layered structure along the a and b directions. The linear trinuclear copper cation in mixed-valence compound 2 consists of one two-valence copper and two one-valence copper atoms which are bridged by admtrz ligands, and the external copper(I) atoms are coordinated by terminal thiocyanate. The EPR spectra of 2 show the existence of localized mixed-valence copper ions. The triangle trinuclear copper cation in compound 3 has its Cu(3) triangle capped by one apical mu(3)-OH group, each edge bridged by a bridging admtrz ligand and each Cu atom coordinated by a N atom from the terminal thiocyanate, while one of the three edges is further bridged by another admtrz ligand and the opposite Cu1 atom is coordinated by a water molecule. The EPR and magnetic susceptibility of compound 3 were studied, showing antiferromagnetic behavior.

Natural and synthetic compounds with kröhnkite-type chains: review and classification

Abstract The crystal structure of kröhnkite [Na2Cu(SO4)2·2H2O], which contains infinite chains composed of CuO6 octahedra corner-linked with SO4 tetrahedra, was originally determined 1952 by Dahlman. Since then, a large number of both minerals (e.g., collinsite, fairfieldite, etc.) and synthetic compounds with closely related struc-tures have been investigated, but the structural relation was not always recognised. In the present review we compare the structures of AnM(XO4)2·2H2O (A = mono- or divalent cation, n = 1, 2; M = di- or trivalent cation; X = penta- or hexavalent cation) compounds with kröhnkite-type infinite chains, and propose a structural classification into six types. The rod group symmetries of the chains are compared. Furthermore, the linkage of these chains to double chains (in krausite-type compounds) and sheets (in yavapaiite-, merwinite-, bafertisite-type and similar structures) is discussed, and the occurrence of octahedral-tetrahedral chains topologically identical to those in kröhnkite (referred to as kröhnkite-type) and similar chains (referred to as kröhnkite-like) in several related compounds is pointed out.

Chemical design of metal-oxide superconductors

The state of art in the field of chemical engineering of high-temperature superconductors is discussed from the point of view of their structural complexity, microstructure and thermodynamic properties. The problems of production of advanced large-grain melt-solidified superconducting ceramics and thick films mostly result from highly anisotropic physical properties, small coherent length, the necessity of artificial pinning center creation and chemical complexity of the materials. The progress in this field is sustained due to better understanding of general preparation principles followed by developing new experimental techniques with precise control of micro-, meso-, nano- and local structures of these cation and anion non-stoichiometric compounds.

Self-assembly of palladium(II) and platinum(II) complexes of 2-hydroxypyrimidine to novel metallacalix[4]arenes. Receptor properties through multiple H-bonding interactions.

Reaction of [enM(H2O)2](NO3)2 (en = ethylenediamine, M = PdII, PtII) with 2-hydroxypyrimidine (Hpymo) in water results in self-assembly to cyclic complexes of type [enM(pymo-N1,N3)]4(NO3)4 (1, M = PdII; 2, M = PtII) which are structurally analogous to calix[4]arenes. The tetranuclear cations in compounds 1 and 2 adopt, in the solid state, a 1,3-alternate orientation of the pymo residues. Attempts to coordinate either soft (PdII, PtII), borderline (CuII, ZnII), or hard (LaIII, BeII, NaI) metal ions to the oxo surface of the metallacalix[4]arene lower rim were fruitless. In fact, X-ray studies performed on [[enPt(pymo-N1,N3)]4(ClO4)4]2.[Cu(H2O)6](ClO4)2.9H2O (4) showed that multiple H-bonding interactions between the water coordination sphere of the copper center and the oxo surface of two tetranuclear cations take place instead of a direct interaction between the heterometal and the oxo surface of the metallacalix[4]arene. Encapsulation of [Cu(H2O)6]2+ is also responsible for the stabilization of the pinched-cone conformation of the tetranuclear cations in 4. pH* dependent 1H NMR spectra of compounds 1 and 2 indicate a very low basicity of the O-donor group of the pymo residues, revealing no protonation of this position down to pH* 0. Moreover, recrystallization of 2 from strongly acidic aqueous solution (approximately 1 M HClO4) affords the adduct [[enPt(pymo-N1,N3)]4(ClO4)4]2.[H20O8](ClO4)4 (6). Analogously to 4, the cationic [H20O8]4+ species is sandwiched between two tetranuclear cations as a result of multiple H-bonding interactions with the oxo surface of two metallacalix[4]arenes. Again a pinched-cone orientation of the pymo residues is realized.

Sterically crowded aryloxides of aluminum: intramolecular coordination of bidentate ligands

Reactions of (BHT) 2Al(H)(Et 2O) (BHT-H=HOC 6H 2-2,6- t Bu 2-4-Me) with HOCH 2CH 2EMe x (E=O, S, x=1; E=N, x=2) yield dimeric species, [(BHT)Al(H)(μ-OCH 2CH 2NMe 2)] 2 ( 2), [(BHT)Al(H)(μ-OCH 2CH 2OMe)] 2 ( 3), [(BHT)Al(H)(μ-OCH 2CH 2SMe)] 2 ( 4), respectively or [(BHT)Al(OCH 2CH 2NMe 2)(μ-OCH 2CH 2NMe 2)] 2 ( 5), [(BHT)Al(OCH 2CH 2OMe)(μ-OCH 2CH 2OMe)] 2 ( 6) and [(BHT)Al(OCH 2CH 2SMe)(μ-OCH 2CH 2SMe)] 2 ( 7), respectively, depending on the stoichiometry of the reaction. The non-bridged donor atoms interact intramolecularly to form five-coordinate aluminum centers. A mixture of (BHT)Li(Et 2O) and (BHT) 2Al(H)(Et 2O), formed from the reaction of LiAlH 4 and BHT-H, reacts with the aforementioned alcohols to yield the monomeric structures (BHT) 2Al(μ-OCH 2CH 2NMe 2) 2Li ( 8), (BHT) 2Al(μ-OCH 2CH 2OMe) 2Li ( 9), (BHT) 2Al(μ-OCH 2CH 2SMe) 2Li ( 10), respectively. If the reaction is carried out with an excess of HOCH 2CH 2SMe, the solvate of compound 10 is formed, (BHT) 2Al(μ-OCH 2CH 2SMe) 2Li(HOCH 2CH 2SMe) ( 11). The lithium cation in compounds 8– 11 is stabilized in the structure by formation of bonds with both the anionic oxygens as well as the neutral donor ligands. The bond valencies have been calculated for Al and Li in compounds 8 and 11.

Synthesis and characterization of photosensitive, dinuclear palladium(I) complexes with 1,1′-bis(diphenylphosphino)ferrocene (dppf), [Pd2(dppf)2(RNC)2]2+ (R=xylyl and mesityl)

Reactions of the dinuclear palladium(I) complex, [Pd 2 (RNC) 6 ](PF 6 ) 2 (R=2,6-xylyl (Xyl), 2,4,6-mesityl (Mes)), with 1,1′-bis(diphenylphosphino)ferrocene (dppf) gave dipalladium(I) complexes with dppf ligands, [Pd 2 (dppf) 2 (RNC) 2 ](PF 6 ) 2 ( 1 , R=Xyl, 66%; 2 , R=Mes, 18%), which were characterized by elemental analysis, 1 H- and 31 P-NMR spectroscopy, IR and UV–vis absorption spectroscopic analyses, and cyclic voltammetry. The structure of 1 was characterized by X-ray crystallography. The cation of compound 1 is composed of two Pd(I) atoms joined by a PdPd σ-bond (2.602(1) A), and each palladium ion has a square planar structure ligated by a terminal isocyanide, two P atoms of dppf, and the neighboring Pd atom. The dppf ligands chelate to the metal with an average PPdP bite angle of 99.19° and an average Pd⋯Fe distance of 4.236 A. The cyclopentadienyl rings of dppf ligands are in staggered form. The 1 H- and 31 P-NMR and the electronic absorption spectra of 1 and 2 indicated that the metalmetal bonded structure as observed in the crystal of 1 was retained in the solution. Complexes 1 and 2 were extremely photosensitive, and underwent a homolytic cleavage even under a room light. The reaction was monitored by the electronic absorption spectral changes and might generate a cation radical, [Pd(dppf)(RNC)] + . The cyclic voltammograms of 1 and 2 in acetonitrile solution showed two successive quasi -reversible oxidation waves at E 1/2 =0.60, 0.72 V (vs. Ag/AgPF 6 ) ( 1 ) and 0.62, 0.73 V ( 2 ) and an irreversible reduction wave at E 1/2 =−1.23 V ( 1 ) and −1.22 V ( 2 ). The former oxidation waves can be assigned to Fe(II)/Fe(III) processes of the two ferrocenyl groups and demonstrated that a charge-transfer communication between the Fe centers occurred through the PdPd single bond.

Salts of the bis(catecholato)borate anion with rhodium– and iridium–phosphine complex cations

In a series of five salts with rhodium- or iridium-phosphine complex cations {cis-chlorohydridotetrakis-(triethylphosphine) iridium (III) bis(pyrocatecholato -O,O')borate, [IrCIH(C 6 H 15 P)4](C 12 H 8 BO 4 ), (1); transchlorobis[ethylenebis(diphenylphosphine)]hydridorhodium(III) bis(pyrocatecholato-O,O')borate dichloromethane solvate, [RhClH(C 26 H 24 P 2 ) 2 ](C 12 H 8 BO 4 ).CH 2 -Cl 2 , (2); trans-chlorobis[ethylenebis(dicyclohexylphosphine)]hydridorhodium(III) bis(pyrocatecholato-O,O')-borate tetrakis(dichloromethane) solvate, [RhClH(C 26 -H 48 P 2 ) 2 ](C 12 H 8 BO 4 ).4CH 2 Cl 2 , (3); tetrakis(trimethylphosphine)rhodium(I) bis(pyrocatecholato-O,O')borate, [Rh(C 3 H 9 P) 4 ](C 2 H 8 BO 4 ), (4); and cis-dihydridotetrakis-(trimethylphosphine)rhodium(III bis(pyrocatecholato -O,O')borate, [RhH 2 (C 3 H 9 P) 4 ](C 12 H 8 BO 4 ), (5)}, the bis-(catecholato)borate anion has approximate D 2d (42m) symmetry, with the central spiro-B atom distorted from regular tetrahedral coordination geometry by reduction of the two intra-ring O-B-O bond angles. The two chelate rings show small deviations from planarity by folding about the O…O axis. The hydrido and chloro ligands in the cation of compound (1), which has four monodentate phosphine ligands, are cis to each other, but in compounds (2) and (3), each with two chelating diphosphine ligands, they are mutually trans. The cation in compound (4) has only four phosphine ligands, which are arranged in a tetragonally distorted square-planar arrangement to minimise steric crowding. Its reaction product with molecular dihydrogen, compound (5), has a cis arrangement of the two hydrido ligands in a distorted octahedral cation. The strong trans influence of the hydrido ligands is reflected in lengthened bonds to the opposite ligands in each case.

Synthesis and crystal structures of the heptamagnesium cationic and mixed magnesium(II)/nickel(II) molecular 2-tetrahydrofurfuroxo aggregates

Direct reaction of metallic magnesium with 2-tetrahydrofurfuryl alcohol (THFFOH) produces the alkoxo magnesium compound of composition Mg(THFFO)2, 1. Compound 1 reacts with FeCl2 and NiCl2 to create two different species: the ionic [Mg7(µ3,η2-THFFO)6(µ,η2-THFFO)6][FeCl4]·3CH2Cl2, 2, and the mixed [(MgII/NiII)4(µ3,η2-THFFO)4Cl4(C2H5OH)4]·0.5C2H5OH molecular complex 3, respectively. Complexes 2 and 3 have been structurally characterized. The cation of compound 2 consists of a Mg7 unit comprising a central Mg atom held within a Mg6 puckered hexagon by six µ3-O(alkoxo) groups from the THFFO ligands. Complex 3 consists of four crystallographically independent distorted octahedral metal sites, distributed unequally (Mg0.7 and Ni0.3), which together with alkoxo oxygen atoms form a cubane-like framework.

Interpretation of the reactivity of peroxidase compounds I and II with phenols by the Marcus equation

The catalytic cycle of heme peroxidases involves two reactive states, compound I and compound II. Although their reduction potentials at pH 7 are similar, compound I is in general more reactive towards organic substrates than compound II. The different reactivities have until now remained unexplained. In this study, the reactions of compounds I and II of peroxidase from horseradish with phenols were analyzed using the Marcus equation of electron-transfer. Both reactions exhibit similar reorganization energies, and the different reactivities of the two enzyme states can be ascribed to a higher apparent rate of activationless electron-transfer in the compound I reactions. This can be attributed to the shorter electron-tunneling distance on electron-transfer to the porphyrin radical cation in compound I, compared to electron-transfer to the iron ion in compound II.

<sup>23</sup>Na NMR Study on the Doped NASICON System

The sodium positions in the doped NASICON solid solution Na3Zr2-xYxSi2-xP1+xO12 system were investigated by using Na-23 NMR techniques. The results of NMR indicates that the surroundings of the sodium cations in compounds with different compositions are different because the network structures are disordered by replacement of Y3+ for Zr4+ ions in the crystal structure. While the composition x is small, the sodium cations locate at two sites, Na(1) and Na(2) sites, in the structure. With x increasing, the surroundings of the sodium cations change and the position of the sodium cations is of only one kind at x=1.2. These results are important for understanding the crystal rule and the effect of the doped cation on the surroundings of the sodium cations in Na3Zr2-xYxSi2-xP1+xO12 solid state solution system.

Characterization of the Glycine-Dependent Redox-Cycling Activity in Animal Fluids and Tissues Using Specific Inhibitors and Activators: Evidence for Presence of PQQ

Pyrroloquinoline quinone, a redox cofactor first isolated from bacteria, efficiently catalyzes the nonenzymatic oxidation of glycine in the presence of nitroblue tetrazolium. We report that certain metalic cations and heterocyclic aromatic cations, like the N-methyl phenazonium cation and aryl-iodonium compounds, strongly and specifically inhibit this redox-cycling activity. The inhibition by metal cations is reversed by Tiron and that of the aromatic cations by Tiron and thyroxine. These inhibitors and activators affect authentic PQQ and the redox-activity of putative PQQ isolated from biological sources in a similar manner. This indicates that pyrroloquinoline quinone occurs naturally in animal tissues and fluids.

KRISTALLSTRUKTUR EINES DIMETHYLAMINO(DIFLUOR)SUBSTITUIERTEN PHOSPHOLIDINIUM-KATIONS MIT DER N,N,N′-TRIMETHYLETHYLENDIAMINEINHEIT

Abstract The cations of compounds 1 and 2 exhibit dynamic behaviour in solution at room temperature; the two fluorine atoms cannot be distinguished by 31P n.m.r. spectroscopy.31 P n.m.r. spectra of 2 at −20°C indicate non-equivalence of the fluorine atoms, and the intramolecular exchange process is slowed down. A low temperature X-ray crystal structure analysis of 2 confirms the expected geometry of the cation. The phosphorus atom displays trigonal bipyramidal coordination geometry, with the chelating ligand spanning one equatorial (NMe, P–N 164.4 pm) and one axial (NMe, P–N 198.7 pm) site at phosphorus.

Ring Expansion Reaction of Heterocyclic Cation Compounds by Incorporating One Nitrogen Atom Using I2–NH3 System

Abstract The reaction of various heterocyclic cation compounds with I2/NH4OH resulted in ring expansion on nitrogen atom. The similar ring expansion reaction occurred on the corresponding triiodides with NH4OH. The reaction mechanism based on initial nucleophilic attack of NH3 on cations, subsequent oxidative iodination, and liberation of I− is proposed.

The National Library of Medicine and Medical Informatics

Medical informatics attempts to provide the theoretic and scientific basis for the use of automated information systems in biomedicine. Even though a new field, its roots are in the 19th century. The National Library of Medicine (NLM) began classifying the medical literature and publishing the Index Medicus in 1897; in the early 1960s, the growth of the index gave rise to MEDLARS, the first successful, large-scale, computerized bibliographic system. In 1971, about the time MEDLARS evolved into a nationwide on-line retrieval system known as MEDLINE, a committee of the Association of American Medical Colleges published a report calling for the NLM to exert strong leadership in developing computer applications for information transfer in medicine. The NLM has sponsored several training and research programs in this area and is now developing the concept of "centers of excellence" in medical informatics. In addition, there are a number of current research and development activities within the NLM internal and extramural programs that may influence the progress of medical informatics.