shows evidence of slow-relaxation in contrast to 2-Yb, it is not a result of exchange biasing because the hysteresis is spindle-shaped and still closed at zero field. We conclude that there are relaxation processes other than QTM that prevent 2-Yb and 4-Yb from being SMMs. The hysteresis and frequency dependence of the ac susceptibility under 1 kOe dc field in 4-Yb is attributed to processes occurring within the exchange states.