Dalton Transactions PAPER Cite this: DOI: 10.1039/c7dt00511c Received 10th February 2017, Accepted 30th March 2017 DOI: 10.1039/c7dt00511c rsc.li/dalton Synthesis of copper hydride (CuH) from CuCO 3 ·Cu(OH) 2 – a path to electrically conductive thin films of Cu† Cláudio M. Lousada, * a Ricardo M. F. Fernandes, b Nadezda V. Tarakina c and Inna L. Soroka b The most common synthesis methods for copper hydride (CuH) employ hard ligands that lead to the for- mation of considerable amounts of metallic Cu as side-product. Here we explore a synthesis method for CuH(s) through the reaction of CuCO 3 ·Cu(OH) 2 (s) with hypophosphorous acid (H 3 PO 2 ) in solution, via the formation of the intermediate Cu(H 2 PO 2 ) 2 (aq) complex. The reaction products were characterized with XRD, FTIR and SEM at different reaction times, and the kinetics of the transformation of Cu(H 2 PO 2 ) 2 (aq) to CuH(s) were followed with NMR and are discussed. We show that our synthesis method provides a simple way for obtaining large amounts of CuH(s) even when the synthesis is performed in air. Compared to the classic Würtz method, where CuSO 4 is used as an initial source of Cu 2+ , our synthesis produces CuH par- ticles with less metallic Cu side-product. We attribute this to the fact that our reaction medium is free from the hard SO 4 2- ligand that can disproportionate Cu(I). We discuss a mechanism for the reaction based on the known reactivity of the reagents and intermediates involved. We explored the possibility of using CuH(s) for making electrically conductive films. Tests that employed water-dispersed CuH particles show that this compound can be reduced with H 3 PO 2 leading to electrically conductive thin films of Cu. These films were made on regular office paper and were found to be Ohmic conductors even after several weeks of exposure to ambient conditions. The fact that the synthesis reported here produces large amounts of CuH particles in aqueous media, with very little impurities, and the fact that these can then be converted to a stable electrically conductive film can open up new applications for CuH such as for printing electrically conductive films or manufacturing surface coatings. 1. Introduction First synthesized by A. Würtz in 1844, copper(I) hydride (CuH) is the oldest known transition metal hydride. 1 In spite of this, CuH was not studied in the early days, in part due to its low thermal stability and high sensitivity to the surrounding environment. 2 The identification of a metal hydride complex was first done almost a century later by Hieber, in the 1930s, and the acceptance of the existence of the metal–H bond hap- pened in the 1950s. 3 In 1964 the structure of a solid hydride was characterized for the first time for K 2 ReH 9 , followed by K 2 TcH 9 . 4–6 Since then, a large number of hydrides have been synthesized and characterized. The foremost reason for the scientific interest around these compounds is that they have unique features because H is the simplest ligand, and in spite of that, hydrides show a remarkable variation in structure and reactivity. 7 As such, they also provide an interesting ground for fundamental research. Additionally, they are also intermedi- ates in biological and geological processes and are of impor- tance for technical applications such as catalysis. 8–10 More recently, hydrides have been classified as a potential hydrogen storage media. 11,12 Binary transition metal hydrides do not occur often in nature and their synthesis and characterization happened later when compared to other classes of transition metal com- pounds. Copper hydride is within the group of the less stable transition metal hydrides of the binary type. 7 There is however an interest in finding ways to obtain this hydride in media that could open up possibilities for the study of its properties and possible applications. At present, the most common synthetic † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c7dt00511c a Division of Materials Technology, Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden. E-mail: cmlp@kth.se; Tel: +(46) 879 06 252 b School of Chemical Science and Engineering, Applied Physical Chemistry, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden c The NanoVision Centre, School of Engineering and Materials Science, Queen Mary University of London, Mile End, London E1 4NS, UK This journal is © The Royal Society of Chemistry 2017 Dalton Trans. Published on 30 March 2017. Downloaded by KUNGL TEKNISKA HOGSKOLAN on 14/04/2017 12:37:05. View Article Online View Journal