  High resolution inelastic neutron scattering is used to study excitations in
the organometallic magnet DMACuCl$_3$. The correct magnetic Hamiltonian
describing this material has been debated for many years. Combined with high
field bulk magnetization and susceptibility studies, the new results imply that
DMACuCl$_3$ is a realization of the $S=1/2$ alternating
antiferromagnetic-ferromagnetic (AFM-FM) chain. Coupled-cluster calculations
are used to derive exchange parameters, showing that the AFM and FM
interactions have nearly the same strength. Analysis of the scattering
intensities shows clear evidence for inter-dimer spin correlations, in contrast
to existing results for conventional alternating chains. The results are
discussed in the context of recent ideas concerning quantum entanglement.
