Tailoring Precursors for Deposition: Synthesis, Structure, and Thermal Studies of Cyclopentadienylcopper(I) Isocyanide Complexes

Abstract

We report here the synthesis and characterization of a family of copper(I) metal precursors based around cyclopentadienyl and isocyanide ligands. The molecular structures of several cyclopentadienylcopper(I) isocyanide complexes have been unambiguously determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl isocyanide complex [(η(5)-C5H5)Cu(CN(i)Pr)] (2a) and the tert-butyl isocyanide complex [(η(5)-C5H5)Cu(CN(t)Bu)] (2b) as possible copper metal chemical vapor deposition (CVD) precursors. Further modification of the precursors with variation of the substituents on the cyclopentadienyl ligand system (varying between H, Me, Et, and (i)Pr) has allowed the affect that these changes would have on features such as stability, volatility, and decomposition to be investigated. As part of this study, the vapor pressures of the complexes 2b, [(η(5)-MeC5H4)Cu(CN(t)Bu)] (3b), [(η(5)-EtC5H4)Cu(CN(t)Bu)] (4b), and [(η(5)-(i)PrC5H4)Cu(CN(t)Bu)] (5b) over a 40-65 °C temperature range have been determined. Low-pressure chemical vapor deposition (LP-CVD) was employed using precursors 2a and 2b to synthesize thin films of metallic copper on silicon, gold, and platinum substrates under a H2 atmosphere. Analysis of the thin films deposited onto both silicon and gold substrates at substrate temperatures of 180 and 300 °C by scanning electron microscopy and atomic force microscopy reveals temperature-dependent growth features: Films grown at 300 °C are continuous and pinhole-free, whereas films grown at 180 °C consist of highly crystalline nanoparticles. In contrast, deposition onto platinum substrates at 180 °C shows a high degree of surface coverage with the formation of high-density, continuous, and pinhole-free thin films. Powder X-ray diffraction and X-ray photoelectron spectroscopy (XPS) both show the films to be high-purity metallic copper.

Copper(I) oxalate complexes: Synthesis, structures and surprises

“…The IR spectrum of this compound showed, in addition to intense oxalate C=O stretching bands at 1622 and 1602 cm -1 , a pair of bands in the N-H/O-H stretching region at 3430 and 3192 cm -1 . Interestingly, the crystal structure of this blue compound revealed that it was not simply the copper(II) dppds complex, as might have been expected, but a smaller copper(II) di-(2-picolyl)amine oxalate complex (12), entirely devoid of sulfur, as shown in Figure 13. In the solid-state structure of complex 12, each copper center is  3 -coordinated by one molecule of di-(2-picolyl)amine,  2 -coordinated by one planar oxalate anion, and  1 -coordinated by a second oxalate ion (in the same plane as the first), which is in turn  2 -coordinated to a neighboring copper center.…”

“…Cu(di-(2-picolyl)amine)C2O4•H2O (12) An attempt was made to isolate the copper(I) oxalate complex with the mixed NxSy ligand dppds by allowing Cu2O to react with oxalic acid in ethanol in the presence of the ligand. This complex is of interest in bioinorganic chemistry [36,37].…”

“…The foregoing copper(I) oxalate complexes were synthesized by a variety of methods, e.g., acid-base reaction of oxalic acid with Cu2O in the presence of ligand; metathesis between a Cu(I) acetylacetonate complex and oxalic acid; ligand exchange with an alkyne or CO complex; reaction of a methylcopper(I) species with oxalic acid; electrochemical reaction of copper with oxalic acid; or metathesis between tetraalkylammonium oxalate and a tetrakisacetonitrile copper(I) salt in the presence of ligand. Among these various routes to copper(I) oxalate complexes, the most "synthetically unpretentious strategy" [12] is the first. The direct reaction of oxalic acid with Cu2O in the presence of ligand has a number of other advantages besides its simplicity: both oxalic acid and Cu2O are cheap and readily available; benign water is the only byproduct; Cu2O is purely basic [13], so side reactions from amphoteric behavior of the base are avoided; the disappearance of the vivid red solid Cu2O starting material is a built-in means of monitoring the reaction; and Cu2O is a strong enough base to react even with amine ligands that have formed solid salts with oxalic acid in the reaction mixture.…”

Cobalt(I) Olefin Complexes: Precursors for Metal–Organic Chemical Vapor Deposition of High Purity Cobalt Metal Thin Films

“…We have previously investigated the relationship between alkyl group functionalization of the cyclopentadienyl ligand and both volatility and stability in copper cyclopentadienide isocyanate complexes . If we compare the temperatures at which the onset of volatilization is observed for the 10 compounds for which both the cyclopentadienyl and methyl cyclopentadienyl complex was synthesized, the general trend appears to be that the addition of a methyl substituent onto the {Cp} fragment results in a lowering of the temperature at which mass loss begins [ 1 (73 °C): 7 (62 °C); 2 (73 °C): 8 (64 °C); 4 (92 °C): 9 (86 °C); 6 (119 °C): 11 (77 °C)].…”

Characterization of Cu-ligand bonds in tris-pyrazolylmethane isocyanide copper(I) complexes based upon combined X-ray diffraction and theoretical study

“…Current progress in the synthesis of (RNC)Cu I compounds allows the classification of the reported species to the following types, viz. homoleptic species [Cu(CNR) n ] + (n = 3 and 4) [29,30] and mixed-ligand complexes bearing, apart isocyanide ligand(s), different C- [31][32][33], N- [34][35][36][37], X-(X = halogen) [38] and other donor ligands [39,40]. To the best of our knowledge, no theoretical studies focused on elucidation of ligand properties and activation of RNC species by copper(I) centers are known.…”