  We present data on the magnetic properties of two classes of layered spin
S=1/2 antiferromagnetic quasi-triangular lattice materials:
$Cu_{2(1-x)}Zn_{2x}(OH)_3NO_3$ ($0 < x < 0.65$) and its long chain organic
derivatives $Cu_{2(1-x)}Zn_{2x}(OH)_3(C_7H_{15}COO)\cdot mH_2O$ ($0 < x <
0.29$), where non-magnetic Zn substitutes Cu isostructurally. It is found that
the long-chain compounds, even in a clean system in the absence of dilution,
$x\!=\!0$, show spin-glass behavior, as evidenced by DC and AC susceptibility,
and by time dependent magnetization measurements. A striking feature is the
observation of a sharp crossover between two successive power law regimes in
the DC susceptibility above the freezing temperature. Specific heat data are
consistent with a conventional phase transition in the unintercalated
compounds, and glassy behavior in the long chain compunds.
