Deutsche Börse said it would take the European Commission to court to try to overturn its decision last month to block its tie-up with NYSE Euronext, in what would have been the world\'s largest exchange deal. The move, rare in European merger cases, came after weeks of bitter recriminations after the Commission voted to stop the deal on antitrust grounds. Börse chief executive, Reto Francioni, called the decision at the time \"a black day for Europe\". The legal action is all the more unusual because NYSE is not taking part, leaving the German exchange to strike out on its own with a potentially protracted legal challenge. \"We have not reached a formal decision on whether to appeal and therefore are not making any comment,\" NYSE said. The Commission\'s antitrust authorities blocked the proposed $9bn tie-up because the combination of the two exchanges\' derivatives businesses, Eurex and Liffe, would have dominated the region\'s derivatives markets, shutting out rivals. The Börse and NYSE countered that the combination would create a \"European champion\" to counter big US exchanges and emerging derivatives exchanges in Asia. They also argued that the combination would still face stiff competition from CME Group of the US, disagreeing with Brussels\' view that the derivatives markets were European, not global, for the purpose of assessing the market dominance of the merger. The Borse said it had decided to sue the Commission at the \"general court\" in Luxembourg. \"Deutsche Börse is of the view that several aspects of the decision are flawed,\" the Börse said on Monday evening. Lawyers said the German exchange would face an uphill struggle proving that the Commission\'s decision was wrong. \"They are looking at a year or so probably,\" said one antitrust lawyer. However the move underscores frustration at the antitrust authorities\' market definition - a view shared by many in the derivatives industry. The lawyer, who was not acting for either exchange, said the Borse\'s move \"sounds like pure optics and annoyance\". The failure of the Börse-NYSE has prompted both exchanges to re-assess their plans for growth as standalone businesses as the sector has soured on the value of mergers. NYSE said last week it was making progress building up its own clearing house in London, where the exchange business has already been thrown into flux by the London Stock Exchange\'s attempt to take control of LCH.Clearnet, a clearing house in which NYSE has a 9 per cent stake. The Börse on Monday said it had proposed Joachim Faber, chief executive of Allianz Global Investors, as the next chairman of the exchange group\'s supervisory board.