Transition-metal rich micas offer interesting properties with regard to magnetism and electric conductivity and moreover allow for a post-synthesis modification of the layer charge by oxidation which makes them interesting for a variety of applications. In this line, a Co and F-rich Cs-mica analogue of tainiolite, Cs(Co22+Li)Si4O10F2, was synthesized by high-temperature melt synthesis. Subsequent annealing for 10 days yielded an almost pure, coarse-grained material. Single-crystal X-ray diffraction studies of the Co-tainiolite showed the structure to be of the 1M polytype (C2/m (No.12) with cell parameters of a = 5.3051(11) Å, b = 9.1710(18) Å, c = 10.897(2) Å, β = 99.40(5)°, V = 523.05(18) Å3. Characteristic geometric parameters were compared to the analogous Mn-rich and Fe-rich compounds. All three compounds are outside the compositional stability limits. Mn-rich Cs-tainiolite, as expected, possesses the smallest octahedral flattening angle, but this value then stays almost constant for Fe- and Co-rich tainiolite although the ionic radius steadily decreases going from Mn2+ over Fe2+, to the smallest Co2+. Rather, the individual octahedral distortions do not show the expected behaviour. Moreover, significant differences between the <T-O>apical (1.607Å) and <T-O>basal (1.658Å) bond lengths may be regarded as the main adjustments mechanism.

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