Facebook, which today has three times as many employees as when it moved to Menlo Park in 2011, is poised to buy 59 acres next to the office building the company is constructing kitty-corner from its main headquarters.

The social media giant recently reached an agreement with TE Connectivity to purchase the 10-building site at 300 Constitution Ave., Facebook spokeswoman Genevieve Grdina confirmed Monday. She would not disclose the purchase price or the company’s specific plans for the property.

“The adjacent property we’ve agreed to purchase is an investment in our future. We have no immediate plans to develop the property,” states a company statement that Grdina provided.

When Facebook first announced in February 2011 that it planned to relocate to the former Sun Microsystems campus in Menlo Park, the company had about 2,000 employees worldwide. Now it has 6,800, Facebook’s website says. About 4,000 of them work in Menlo Park, according to the city’s transportation office. The 57-acre former Sun campus, located at the eastern end of the Willow Road/Bayfront Expressway intersection, can accommodate up to 6,600 employees.

The “West Campus” that Facebook is building on 22 acres across from Bayfront Expressway will be able to handle up to 2,800 employees. Designed by famed architect Frank Gehry, the 435,000-square-foot office building will be crowned with a rooftop park and is expected to be completed by spring 2015.

Facebook’s expansion into Menlo Park’s eastern side also involves residential development. The company collaborated with developer St. Anton Partners to help design a 394-unit apartment complex that’s about a mile away at 3665 Haven Ave. Another developer, Greystar, has applied to build a 146-unit apartment complex next door at 3645 Haven Ave. Those residential projects, plus a seven-building apartment complex with 195 units at 721-881 Hamilton Ave. in the adjacent Belle Haven neighborhood, are expected to be attractive living options for Facebook’s young and growing workforce.

Email Bonnie Eslinger at beslinger @dailynewsgroup.com; follow her at twitter.com/bonnieeslinger.