Associating an account as Parent Account to an existing account.

Associating an account as Parent Account to an existing account.

I added an account and want to add a parent account to it. I tried to set Parent_Account field. Its a LookUp type of field. 
Below is my code.
"record.SetProperty("Parent_Account", serviceAccnt.Parent_Account);".. where serviceAccnt.Parent_Account is the same object that we get from Parent Account inside the account.

This is not working. I can set string and int type of field but not LookUp type of field.

Is there any other way to set a "LookUp" type of field.?? 
OR
Please tell how to add a Member Account usng C# SDK.

Thanks