Measurement and calculation of the superexchange interaction through the two-halide bridge in the eclipsed layered compounds $\left[\mathrm{N}{\mathrm{H}}_3{\left(\mathrm{C}{\mathrm{H}}_2\right)}_n\mathrm{N}{\mathrm{H}}_3\right]\mathrm{Cu}X$ for $n=2-5\mathrm{}$ and $X={\mathrm{Cl}}_4 \mathrm{and} {\mathrm{Cl}}_2{\mathrm{Br}}_2$

Magnetic susceptibility measurements on the eclipsed layered structure series of $\left[\mathrm{N}{\mathrm{H}}_3{\left(\mathrm{C}{\mathrm{H}}_2\right)}_n\mathrm{N}{\mathrm{H}}_3\right]\mathrm{Cu}X$ ($n=2, 3, 4, \mathrm{and} 5$ for $X={\mathrm{Cl}}_4$ and $n=2\mathrm{}$ for $X={\mathrm{Cl}}_2{\mathrm{Br}}_2$) indicate that the interplanar superexchange interaction along the linear Cu-Cl-Cl-Cu path has a significantly stronger Cu-Cu distance dependence than that for the typical $M-X-M$ ($M=\mathrm{C}\mathrm{u},\mathrm{M}\mathrm{n},\mathrm{N}\mathrm{i},\mathrm{C}\mathrm{o}$; $X=\mathrm{F},\mathrm{C}\mathrm{l}$) path, and a stronger power-law metal-metal distance dependence than previously expected for the two-halide bridge case. Furthermore, the evidence indicates a 10th-power dependence on the halide-halide separation, which appears to be the critical parameter for determining the strength of the two-halide superexchange. Previously unpublished data on the partially bromated compound is included. The results of a Rayleigh-Schrödinger perturbation calculation of the two-halide superexchange strength are presented and the calculated results are compared with experimental values.