Cobalt cyanoaurate (I) Colsqb;Au(CN)2rsqb;2is a new material derived from cobalthyphen;hardened gold electroplating bath solutions that crystallizes in the hexagonal system with space groupP6422 and six formula weights in a unit cell witha= 8.434plusmn;0.004 andc= 20.695plusmn;0.006 Aring; at 298 K. The integrated intensities of a full sphere of reciprocal space, within a radius of (sinthinsp;Vthgr;)/lgr; = 0.85 Aring;minus;1, were measured using graphite monochromated MoKagr; with a CADhyphen;4 diffractometer. The resulting total of 12thinsp;037 structure factors gave 1969 terms after averaging, of which 717 were accepted as reliably observed. Patterson and Fourier series were used to solve the crystal structure, which was refined by the method of least squares: the final agreement factorR= 0.0358. The atomic thermal vibrations are highly anisotropic. The Au(CN)minus;2ion departs slightly but significantly from linearity with a Cndash;Aundash;C angle of 173.1plusmn;1.5deg; and mean Aundash;Cndash;N angle of 170.6plusmn;1.7deg;. The cyano groups also form tetrahedral Co(NC)2minus;4ions: conversion to the octahedral Co(NC)2minus;6ion occurs at high concentrations of K+in solution. The crystal radius of highhyphen;spin Co(II) decreases by 0.15 Aring; as the coordination changes from octahedral to tetrahedral, for a twohyphen;coordinated N radius of 1.245 Aring;. The mean Aundash;C distance is 2.003plusmn;0.016 Aring; with Cndash;N = 1.124plusmn;0.021 Aring; and Condash;N = 1.973plusmn;0.013 Aring;. The mismatch between Aundash;Au separations in Colsqb;Au(CN)2rsqb;2and in (111) of elementary Au is less than 8percnt;. The identical but rotated sequence of Aundash;Au separations at thec/3 and 2c/3 levels in Colsqb;Au(CN)2rsqb;2coincides within 2.4percnt; with the corresponding spacings in the element normal to (111) at theasqrt;3 and 2asqrt;3 levels. These small mismatches could result in epitaxial overgrowth leading to gold hardening and incorporation of the observed impurities in the electrodeposit.
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