Google Inc raised its offer for Motorola Mobility Holdings Inc by 33 percent to $12.5 billion over two weeks of negotiations between the two companies, according to a regulatory filing on Tuesday.

Google originally offered $30 for every Motorola share on August 1 -- but eventually paid $40 -- as the Internet powerhouse sought Motorola's massive patent portfolio, after losing out on the Nortel patent auction to a consortium including Apple and Microsoft.

On August 5, Frank Quattrone's Qatalyst Partners, who advised Motorola on the deal, suggested the company reject the initial bid and seek an offer of $43.50 a share instead, according to a filing by Motorola with the U.S. Securities and Exchange Commission.

On August 9, Google came back with an offer of $37 per share, but Sanjay Jha, Motorola's CEO, said he would be prepared to recommend that the company consider accepting an offer of $40.50 a share or higher.

On the same day, Google raised its price to $40 per share, and proposed to start due diligence and announce the merger by August 14.

The companies ultimately announced the merger on August 15, settling at $40 per Motorola share -- a 63 percent premium to Motorola's previous trading day close.

(Reporting by Abhiram Nandakumar, Brenton Cordeiro and Savio D'Souza in Bangalore; Editing by Gary Hill)

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