Alexis Sánchez settled into his new surroundings at Manchester United and immediately took aim at former Arsenal players.

The swap deal which had been talked of exhaustively finally came to fruition on Monday with Sánchez making the move to Old Trafford and Henrikh Mkhitaryan heading to north London.

Sánchez claimed he left Arsenal for the same reason as Thierry Henry, the club’s record scorer, departed for Barcelona in 2007, to better his career and, in the same Instagram post, directed unhappiness at former players who had criticised the decision.

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Last week Martin Keown branded Sánchez “football’s biggest mercenary” and Ian Wright claimed in December he had “clocked off”. Sánchez said: “There are people (former club players) who have spoken with no knowledge of what happens inside the club and cause damage. I must say I always gave 100%, until the last day, when I asked to the Mister [Arsène Wenger, the manager] to be in the team, because I wanted to be a contribution.”

Sánchez referred to Henry, who won the Champions League and two La Liga titles at Barcelona. “I remember today, a conversation I had with Henry, a historic Arsenal player, who changed club for the same reason and today is my turn,” he said.

The 29-year-old did offer gratitude to Arsenal, where he won two FA Cups in his three full seasons. “Thanks for everything Gunners. All we achieved and the good moments that I gave to the club, I want to dedicate it to the fans, they are the most important. Thanks for every time you sing ‘Alexis Sánchez Baby’. I want to say thanks to the technical staff, to the medical team and all team-mates with whom I shared many nice things for the club and especially those people who do not see themselves on the covers, but without them nothing would be possible, which are there to prepare food for us and take care of us day by day, those who keep our shoes clean and the grass in the best conditions. Many thanks to you for helping us to improve every day. Thank you very much.”

Sánchez’s four-and-a-half-year contract ties him to United until the summer of 2022. It is understood his salary is closer to a basic £300,000 a week than the reported £500,000. This means he is, with Zlatan Ibrahimovic, the club’s highest remunerated player. The transfer is priced at around £60m once United’s £35m valuation of the Armenian plus the fee received by the Chilean and his agent is factored in. Sánchez will wear club’s iconic No 7 shirt, which has been vacant since Memphis Depay was sold to Lyon last January.

Of the move Sánchez said: “I am thrilled to be joining the biggest club in the world. I have spent three‑and‑a‑half wonderful years at Arsenal and I bring with me very positive memories of that great club and its fans. The chance to play in this historic stadium [Old Trafford] and to work with José Mourinho was something I could not turn down. I am very proud to be the first Chilean player ever to play for United’s first team and I hope I can show our fans all around the world why the club wanted to bring me here.”

Mourinho said: “Alexis is one of the best attacking players in the world and he will complete our very young and talented group of attacking players. He will bring his ambition, drive and personality, qualities that make a Manchester United player and a player that makes the team stronger and the supporters proud of their club dimension and prestige.”

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A club statement confirmed that Mkhitaryan had left for Arsenal just 18 months after Mourinho bought him from Borussia Dortmund for around £27m. “Manchester United is delighted to announce the signing of Alexis Sánchez from Arsenal in a deal that sees the Armenian midfielder Henrikh Mkhitaryan move in the opposite direction,” it said.

Of the Armenian’s departure Mourinho said: “I would like to wish Henrikh all the success and happiness that I am sure he is going to get. He is a player that we will not forget, especially for his contribution to our Europa League victory.”

The player, who turned 29 on Sunday, stated it was a “dream” to join Arsenal. “I’m very happy that we could finish this deal and I’m very happy to be here. It’s a dream come true because I’ve always dreamed of playing for Arsenal. Now that I’m here, I’ll do my best for this club to create history,” he told the club website. “I always loved the way that Arsenal played and the way that Arsène Wenger has managed the team. There have been a lot of young players, he’s managed them and they’ve done very well. Of course I was in love with the game of Thierry Henry I loved the way he played – and maybe that was the reason to support Arsenal.”