Mixed system $C{s}_{3}C{u}_{3}C{l}_{8-x}B{r}_{x}OH$ with weakly connected Cu-triangles

To study the relationship between the properties of low-dimensional spin systems with weakly coupled Cu-triangles and their crystal structure, single crystals of $C{s}_{3}C{u}_{3}C{l}_{8}OH$ (1) and the new $C{s}_{3}C{u}_{3}C{l}_{7.6}B{r}_{0.4}OH$ (2) were grown. Both compounds are isostructural and crystallize in a monoclinic structure with space group $P{2}_1\mathrm{/}c$. The magnetic susceptibility of (1) shows a maximum at $2.23K$ and of (2) at $2.70K$, which are attributed to antiferromagnetic phase transitions. Furthermore, the magnetization along the $b$-axis at $1.9K$ for both compounds shows a spin-flop transition into a new antiferromagnetic phase. This transition occurs at $0.61T$ for (1) and at $2.0 T$for(2)\mathrm{.}Theantiferromagneticordercanbesuppressedbyamagneticfield$B_{C1}= 1.1 T$for(1)and$B_{C2}= 1.2 T$ for (2). First single crystal neutron diffraction measured on (1) at different temperatures reveals the magnetic signal on the top of the nuclear reflection at (-1 0 0). Its magnetic ordering temperature was found to be at $T_{N1}=2.12(3)K$.