Piezoelectric KCo[Au(CN)2]3: Room temperature crystal structure of a cobalt-hardened gold electrodeposition process component

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Abstract
Potassium cobaltous cyanoaurate(I), KCo[Au(CN)2]3, a new piezoelectric material that is also a component in the electrodeposition process for cobalt‐hardened gold, crystallizes in the trigonal system with space group P312 and one formula in the unit cell. The lattice constants at 298 K are a =6.82802±0.00005, c=7.80807±0.00009 Å (λCuKα1=1.540598 Å). The integrated intensities of most reflections within an extant of reciprocal space having radius (sin ϑ)/λ?1.15 Å−1 were measured diffractometrically, resulting in 1130 independent nonzero structure factors. The crystal structure was solved by use of Patterson and Fourier series and refined by the method of least squares, with final agreement factor R=0.0578. The Au(CN)2− ion is close to linear, with Au–C distance of 1.994±0.011 Å, C–N=1.147±0.014 Å, and C–Au–C angle of 178.2±1.7°. The Co2+ ion occupies an octahedral environment, with six equal Co–N distances of 2.124±0.010 Å. The K+ ion is 12‐coordinated with six N atoms at 2.950±0.022 Å and six C atoms at 3.215±0.020 Å. A site with similar environment, but slightly shorter contacts, remains vacant. The piezoelectric d22 coefficient is about 5.8×10−12 CN−1. Possible roles for KCo[Au(CN)2]3 in the hard‐gold electrodeposition process are considered.

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