I dont know why I am helping a grouch, but you didn't give enough info to answer the question. That is why I suspected it was homework.
Since you "measured" the impedance, you should have stated how you measured it, and how the measurement might have effected the network you are testing. Chances are that you used a signal generator, or some sort of vector impedance meter, which drive the circuit under test from a 50Ω source. Unfortunately, the 50Ω source impedance effects the network under test...
Here is a sim of a simple circuit which "sort-of" behaves like you describe. I'll leave it to you to iterate on it until it matches your conditions....
Note that LTSpice plots Im( ) as a Magnitude and angle, so when the angle is less than zero degrees, the value is negative.