And he revealed the club suspected the Brazil forward wanted to leave even as he was signing a new contract in 2016.
The 25-year-old joined PSG for a world record 222m euro (£200m) fee last week following months of speculation.
Bartomeu said: "His way of doing things was not the best. It was not the behaviour we expect of a Barca player."
Neymar has formed part of our club and of our success over the past four years, but he is now history
Josep Maria BartomeuBarcelona president
Neymar refused to speak about his future while rumours he was due to move began to mount.
But on his return to training last Wednesday, he told the club he wanted to leave and was given permission to "sort out his future".
The transfer was completed just two days later, at which point Neymar revealed he wanted a "bigger challenge" and was always drawn by the ambitionshown by the French club and their Qatari owners.
He had signed a new five-year deal in October and Bartomeu said he suspected the player wanted to leave even then: "We predicted Neymar could leave so we raised his buyout clause to 222m euros so we would have a stable future.
"When we started to doubt he would stay, we remained calm because whatever happened would have been good for Barca.
"If he remained, we kept an exceptional player. And if he left then the whole of his buyout clause would have to be paid, which gives us the money to guarantee that we can sign new and competitive players.
"Neymar has formed part of our club and success over the past four years, but he is now history.
"It's been his decision. We did everything in our hands to try to get him to stay - the directors, the players and the coaches."
He added that Barcelona had passed details of the transfer to football's European governing body Uefa because "we are opposed to the artificial inflation of the football market and because we want to protect football and make it sustainable".
Speaking at the annual congress of supporters' clubs, he also compared Neymar's conduct with that of Lionel Messi and Andres Iniesta, who have both spent their entire careers with Barca.
"No player is above Barca, everything has a limit and that is why we did what we did. Messi's loyalty should be an example for everyone who wants to wear our colours, as should Iniesta's," said Bartomeu.
He said the money made from selling Neymar will now be spent with "prudence, rigour and serenity".
Liverpool's Philippe Coutinho, Borussia Dortmund's Ousmane Dembele and PSG's Julian Draxler have been linked with moves to the Nou Camp.
Neymar's departure from Barcelona breaks up the feted attacking trident he formed with Argentina captain Messi and Uruguay forward Luis Suarez. "Now we won't be talking about the Barca of the trident, we'll be focusing more on the team," Bartomeu said.
Neymar scored 105 goals in four seasons at Barca, winning seven major trophies including the Champions League once and La Liga twice.