  We investigate the structural and magnetic properties of two molecule-based
magnets synthesized from the same starting components. Their different
structural motifs promote contrasting exchange pathways and consequently lead
to markedly different magnetic ground states. Through examination of their
structural and magnetic properties we show that
[Cu(pyz)(H$_{2}$O)(gly)$_{2}$](ClO$_{4}$)$_{2}$ may be considered a
quasi-one-dimensional quantum Heisenberg antiferromagnet while the related
compound [Cu(pyz)(gly)](ClO$_{4}$), which is formed from dimers of
antiferromagnetically interacting Cu$^{2+}$ spins, remains disordered down to
at least 0.03 K in zero field, but shows a field-temperature phase diagram
reminiscent of that seen in materials showing a Bose-Einstein condensation of
magnons.

Strongly Correlated Electrons