title: Synthesis and characterization of silver(I) pyrazolylmethylpyridine complexes and their implementation as metallic silver thin film precursors.
abstract: A series of light- and air-stable silver(I) pyrazolylmethylpyridine complexes [Ag(L(R))]n(BF4)n (L = pyrazolylmethylpyridine; R = H, 1; R = Me, 2; R = i-Pr, 3) and [Ag(L(R))(NO3)]2 (L = pyrazolylmethylpyridine; R = H, 4; R = Me, 5; R = i-Pr, 6) has been synthesized and structurally and spectroscopically characterized. In all of the molecular structures, the pyrazolylmethylpyridine ligands bridge two metal centers, thus giving rise to dinuclear (2, 4, 5, and 6) or polynuclear structures (1 and 3). The role played by the counteranions is also of relevance, because dimeric structures are invariably obtained with NO3(-) (4, 5, and 6), whereas the less-coordinating BF4(-) counteranion affords polymeric structures (1 and 3). Also, through atoms-in-molecules (AIM) analysis of the electron density, an argentophilic Ag···Ag interaction is found in complexes 2 and 4. Thermogravimetric analysis (TGA) shows that the thermolytic properties of the present complexes can be significantly modified by altering the ligand structure and counteranion. These complexes were further investigated as thin silver film precursors by spin-coating solutions, followed by annealing at 310 °C on 52100 steel substrates. The resulting polycrystalline cubic-phase Ag films of ∼55 nm thickness exhibit low levels of extraneous element contamination by X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) indicate that film growth proceeds primarily via an island growth (Volmer-Weber) mechanism. Complex 4 was also evaluated as a lubricant additive in ball-on-disk tribological tests. The results of the friction evaluation and wear measurements indicate a significant reduction in wear (∼ 88%) at optimized Ag complex concentrations with little change in friction. The enhanced wear performance is attributed to facile shearing of Ag metal in the contact region, resulting from thermolysis of the silver complexes, and is confirmed by energy-dispersive X-ray analysis of the resulting wear scars.
authors.affiliation: Dipartimento di Chimica, Università degli studi di Parma , Parco Area delle Scienze 17/a, 43100 Parma, Italy.
authors.forename: Irene
authors.initials: I
authors.lastname: Bassanetti
authors.forename: Christina P
authors.initials: CP
authors.lastname: Twist
authors.forename: Myung-Gil
authors.initials: MG
authors.lastname: Kim
authors.forename: Afif M
authors.initials: AM
authors.lastname: Seyam
authors.forename: Hassan S
authors.initials: HS
authors.lastname: Bazzi
authors.forename: Q Jane
authors.initials: QJ
authors.lastname: Wang
authors.forename: Yip-Wah
authors.initials: YW
authors.lastname: Chung
authors.forename: Luciano
authors.initials: L
authors.lastname: Marchió
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Delferro
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks
mesh_terms: D018360:Crystallography, X-Ray; D008855:Microscopy, Electron, Scanning; D008958:Models, Molecular; D066244:Proton Magnetic Resonance Spectroscopy; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry; D018030:Silver Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D011725:Pyridines; D018030:Silver Compounds