Silver Nitrate Complexes of Nitrogen-Containing

Silver Nitrate Complexes of Nitrogen-Containing Heterocycles Hubert Schmidbaur*, Angelika Mair, Gerhard Müller*, Joachim Lachmann+, and Siegfried Gamper+ Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstraße 4, D-8046 Garching Z. Naturforsch. 46b, 912-918 (1991); received February 19, 1991 Silver Complexes, Nitrogen Heterocycles, Pyrazole. Triazole, 8 -Amino-quinoline Pyrazole, 1,2,4-triazole, and 8 -amino-quinoline form complexes as neutral ligands with sil ver nitrate in slightly acidic aqueous medium. With pyrazole a 2:1 complex (1) is obtained. The crystal structure determination revealed an ionic structure with independent N 0 3~ anions and centrosymmetrical (pyr) 2Ag+ cations with a linear coordination geometry at the silver atoms. The reactions with 1,2,4-triazole and 8 -amino-quinoline yield dimeric 1:1 complexes (2, 3), in which the silver atoms are bridged by the ligands and have short contacts with nitrate oxygen atoms. The coordination geometry of the metals can thus be described as distorted tetrahedral. A 1 :1 complex with 2,3-diphenyl-1,2,4-triazole (2a) and a 2:1 complex with 8 -hydroxy-quinoline (4) have also been prepared, but not characterized in detail. Introduction prepared and characterized a series of complexes Complex formation of silver(I) cations by am of silver nitrate with pyrazole, (diphenyl)triazole, monia and amines has been well established in an 8 -amino-quinoline, and 8 -hydroxy-quinoline. alytical chemistry and chemical technology of sil ver for more than a century. However, nitrogen- Preparation and Properties of the Complexes containing heterocycles have also been among the early complexing agents. The first silver “azolides” The complexes were synthesized by mixing were in fact obtained as early as 1893, almost 100 slightly acidic aqueous solutions of AgN0 3 (HNOj) with an ethanol solution of an excess of years ago [ 1 ], and interest in this class of com pounds continued ever since [2, 3], owing to the the ligand. Crystals were grown by slow evapora potential application of these compounds in pho tion of the solvents at room temperature under tography or silver plating by electrochemical or protection against direct incandescence of visible other processes. light. The products have been identified by mi A more detailed knowledge of the stoichiometry croanalysis, 'H and 13C NMR spectroscopy, and and structure of the complexes grew out of X-ray single crystal X-ray diffraction methods. The re diffraction studies, first initiated in 1971 [4], Sever sults of these studies showed that only pyrazole al structures have since been determined [5-9]. forms the 2 : 1 complex expected from a reaction Though in most cases the expected linear two- with excess ligand, while triazole and diphenyl- coordinate geometry at the silver atom could be triazole as well as 8 -amino-quinoline give only the confirmed, there are also examples for species with 1 : 1 complexes: higher coordination numbers and less regular ge A g N 0 3(aq) + 2 C3N 2H 4 — [(C3N 2H 4)2Ag]+NCV ometries, mainly due to contacts with the counter 1 + C 2N 3H 3 - [(C2N 3H 3)A g N 0 3] 2 ions present in the system. 2 As part of a program oriented towards the de + C 2N 3 HPh 2 -> [(C2N 3HPh2)A g N 0 3] 2 velopment of new materials for thermal silver plat 2a + C 9 N-,H8 [(C 9 N 2H 8 )A g N 0 3] 2 ing of substrate surfaces for application in electri 3 cal devices or for decorative purposes, we have According to the analytical and structural data, only complex 1 (melting point 76 °C, colourless * Reprint requests to Prof. Dr. H. Schmidbaur. crystals, 98.0% yield), can be considered an ionic + X-ray diffraction studies. compound, with the cations of 2 : 1 stoichiometry Verlag der Zeitschrift für Naturforschung. D-7400 Tübingen well separated from the nitrate anions both in so 0932-0776/91 /0700-0912/$ 01.00/0 lution and in the crystal (see below). Complexes 2 Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung This work has been digitalized and published in 2013 by Verlag Zeitschrift in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der für Naturforschung in cooperation with the Max Planck Society for the Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Advancement of Science under a Creative Commons Attribution Creative Commons Namensnennung 4.0 Lizenz. 4.0 International License. H. Schmidbaur et al. • Silver Nitrate Complexes of Nitrogen-Containing Heterocycles 913 (colourless crystals, 83.7% yield) and 3 (brown 190 C. When treated with pyridine, compound 4 crystals, 95.2% yield) are associated to give dimers yields the known pyridinium bis( 8 -oxyquinolina- with close contacts between cations and anions. to)silver(I) [ 1 1 ]. The NMR spectra of aqueous solutions of com A g N 0 3(aq) + 2 C 9H 7NO (C 9 H 7 N 0 ) 2Ag+N 0 3~ plex 1 suggest C2v symmetry of each ligand 4 through equivalence of the N-bonded CH groups i + Pyr ('H and 13C), and a first-order 1:2:1 'H triplet for (PyrH)+[(C 9 H 6NO)2 H]Ag- the central CH group (Exper.). This result indi cates a rapid site exchange of silver cations and protons at the four nitrogen atoms of the 2 : 1 com plex. Structural Studies The solid state structures of compounds 1 - 3 H H have been determined by single crystal X-ray dif ^ A fraction. Crystal data and structure solution pa H ZN N\ „ono2 rameters are listed in Table I. Ag Ag For compound 1, the structure of one of two in . » ° 2 N°" n - N dependent and very similar centrosymmetrical I JJ complex cations is shown in Fig. 1. The pyrazole C ~K ] H ligands are attached to the silver atom via one of the two nitrogen atoms. As shown in Fig. 2, the ni OoN 2 0 trate anions have no short contacts with the com plex cations. As illustrated in Fig. 3, the structural unit in the crystals of complex 2 is a centrosymmetrical di mer, with two (4-H)-triazole ligands N,N'-bridg- ing two silver atoms. The two nitrate counterions are coordinated to the metal atoms mainly through one oxygen atom (0 3, 03') at 2.491(1) Ä, For complex 2, the NMR data (in D 20) indicate while oxygen atoms 0 2 , 0 2 ' are further apart (at C2v symmetry for the ligands, but this is also borne 2.803(1) Ä). The silver tetra-coordination can thus out by the crystal structure, where the triazoles be described as strongly distorted tetrahedral. The form symmetrical N,N'-bridges between the silver flat dimeric units are stacked as shown in Fig. 4, atoms. Therefore, no ligand exchange has to be in with the stacks crosslinked by hydrogen bonds voked in order to explain the singlet 'H and 13C (from 4-H of the triazole, at N 2 in the crystallo- CH resonances of the compound, but nevertheless graphic notation of Fig. 3, to O 1 of a nitrate). such an exchange may as yet be operative in polar Crystals of compound 3 also contain centrosym media. The third nitrogen atom, which is not metrical dimeric units, which are shown in Fig. 5. Ag-coordinated, is a protonated donor site. This Two ligands are complexing two silver atoms in a “4H-Form” is also found in analogous copper head-to-tail arrangement, i. e. one amino and one complexes [10]. The diphenyl analogue 2 a is as pyridine function in a trans position at the metal. sumed to be similar in structure, but has not been The coordination at the silver atoms is not linear, investigated any further. however, since a significant distortion occurs The NMR spectra of complex 3 (in D 20 ) show through monodentate coordination of a nitrate only one set of ‘H and 13C resonances, indicating counterion (at 2.435(1) Ä for A g-O 1). A second equivalent ligands. Details are presented in the Ex A g-O contact (Ag-O 3") from an oxygen atom of perimental Part. a neighbouring dimer (Fig. 6 ) is longer, at By contrast, the reaction of AgNO? with 2.728(1) Ä. The coordination of the silver thus also 8 -hydroxy-quinoline in H N 03-acidic aqueous so renders a strongly distorted tetrahedral environ lution affords the 2:1 complex 4 (97.8% yield), ment. Hydrogen bonds between amino groups of which is sensitive to light and decomposes at the ligands and oxygen atoms of the nitrate ions 914 H. Schmidbaur et al. • Silver Nitrate Complexes of Nitrogen-Containing Heterocycles Table I. Crystal data, data collec Complex 1 2 3 tion and refinement of compounds 1-3. Formula C 6 H 8 A gN 50 3 C4 H 6 N 8 A g 20 6 C 18 H l6Ag 2 N 60 6 Formula weight 306.05 477.88 628.10 Space group P 1 triclinic P 2 ,/rc monocl. P 2,/c monocl. Colour colourless colourless orangebrown « (A) 10.723(2) 3.536(1) 8.390(1) b (4 ) 5.314(1) 13.962(1) 15.128(2) c (A) 9.742(2) 11.655(1) 7.691(1) « (°) 110.46(1) 90 90 ß ( ) 103.44(1) 94.33(1) 97.49(1) y Q 80.49(1) 90 90 V (A3) 503.7 573.76 967.8 z 2 2 2 Dcalc (g/cm3) 2.018 2.76 2.15 Data instrument Syntex P2, CAD4 Syntex P2, Radiation M o -K M o -K M o -K // (cm-1) 19.8 34.25 20.55 O 0 U 0 1 1 T of data coll.

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