A Chicago-based real estate company is buying a five-building complex that includes CDW's executive offices. : A Chicago-based real estate company is paying about $75 million for a five-building office complex that includes CDW's executive offices in Lincolnshire.The investment arm of real estate brokerage Bradford Allen has agreed to acquire the Tri-State International Office Center from Des Moines, Iowa-based Principal Real Estate Investors, according to sources familiar with the deal.It's unclear whether Bradford Allen has a financial partner on the acquisition, though the company tends to be more active as a real estate broker than a property investor.