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.

Argentophilic Interactions

“…The compound can be used as a precursor for the deposition of silver thin films on steel. [315] The tetrafunctional ligand 1,2,4,5-tetrakis(benzimidazol-1-ylmethyl)benzene forms tetranuclear complexes with AgNO 3 with pairs of silver atoms in 22-membered rings with transannular Ag-Ag distances of 3.3231(6) and 3.306(1) (in two different solvates, 98, benzimidazoles shown as arcs). [316] 24-Membered rings have been obtained in crystals of the complexes of silver perchlorate or triflate with a double Schiff base of type 96 with di(4-aminophenyl)methane as the parent amine.…”

Synthesis and structural characterization of silver(i), copper(i) coordination polymers and a helicate palladium(ii) complex of dipyrrolylmethane-based dipyrazole ligands: the effect of meso substituents on structural formation

“…These distances are shorter than those observed for complex 5 (see below) and fall within the 1.99(2) Å to 2.149(4) Å range reported for the two coordinate silver(I) complexes bearing pyrazole 30 and multi-pyrazole ligands. 14i, 31 (6), N6-Ag1 2.204 (7), N9-Ag2 2.202 (6), N4-Ag2 2.236 (6), N11-Ag1-N6 125.5(2), N9-Ag2-N4 120.4(2), N1⋯F3 2.809(9), H1n1⋯F3 1.99(5), N1-H1n1⋯F3 158 (7); N2⋯F2 2.882(10), H2n2⋯F2 2.03(4), N2-H2n2⋯F2 166 (7); N7⋯F5 2.975(8), H7n7⋯F5 2.16(4), N7-H7n7⋯F5 159 (6). Symmetry transformations used to generate equivalent atoms: (i) x, y, z -1 and (ii) x, y, z + 1.…”

“…6 The architecture of the coordination polymer 25 remains very sensitive to the orientation of the ligating atoms in the organic molecule, 7 counter ion, 8 metal-to-ligand ratio, 9 and solvents. 10,11 This is coupled with the flexibility of silver metal to adopt different coordination numbers and geometries with noncovalent interactions such as hydrogen bonding and π−π 30 interaction among others.…”

Argentophile Wechselwirkungen

“…Die Verbindung kann als Ausgangsstoff für die Abscheidung von dünnen Silberfilmen auf Stahl verwendet werden. [315] Der tetrafunktionale Ligand 1,2,4,5-Tetrakis(benzimidazol-1-ylmethyl)benzol bildet mit AgNO 3 vierkernige Komplexe mit Paaren aus Silberatomen in 22-gliedrigen Ringen und transannularen Abständen von 3.3231(1) und 3.06(1) (zwei verschiedene Solvate, 98; die Benzimidazole sind als Bçgen dargestellt). [316] In Kristallen der Komplexe von Silberperchlorat oder -triflat mit einer doppelten Schiff-Base des Typs 96 mit Di(4-aminophenyl)methan als dem Mutteramin wurden 24gliedrige Ringe erhalten.…”