Synthesis, characterization, and crystal structure of...

Typical electroless copper baths (ECBs), which are used to chemically deposit copper on printed circuit boards, consist of an aqueous alkali hydroxide solution, a copper(II) salt, formaldehyde as reducing agent, an l-(+)-tartrate as complexing agent, and a 2,2'-bi-pyridine derivative as stabilizer. Actual speciation and reactivity are, however, largely unknown. Herein, we report on the synthesis and crystal structure of aqua-1κO-bis-(4,4'-dimeth-oxy-2,2'-bi-pyri-dine)-1κ² N,N';2κ² N,N'-[μ-(2R,3R)-2,3-dioxidosuccinato-1κ² O ¹,O ²:2κ² O ³,O ⁴]dicopper(II) octa-hydrate, [Cu₂(C₁₂H₁₂N₂O₂)₂(C₄H₂O₆)(H₂O)]·8H₂O, from an ECB mock-up. The title compound crystallizes in the Sohncke group P2₁ with one chiral dinuclear complex and eight mol-ecules of hydrate water in the asymmetric unit. The expected retention of the tartrato ligand's absolute configuration was confirmed via determination of the absolute structure. The complex mol-ecules exhibit an ansa-like structure with two planar, nearly parallel bi-pyridine ligands, each bound to a copper atom that is connected to the other by a bridging tartrato 'handle'. The complex and water mol-ecules give rise to a layered supra-molecular structure dominated by alternating π stacks and hydrogen bonds. The understanding of structures ex situ is a first step on the way to prolonged stability and improved coating behavior of ECBs.