Workplace messaging and collaboration platform Slack has raised $250m in fresh capital, valuing it at $5.1 billion. 

The Series G fundraising is on top of the $591m in funding that it has already secured since it was founded. 

The round was led by SoftBank Vision Fund, along with Accel and a number of other investors.
Slack will employ around 150 people in Dublin by the end of the year.

It said the money was raised to ensure the business can be run with operational flexibility regardless of outside financing conditions and also to prove its stability into the future. 

The firm, founded in 2009, says it has not spent all the money it raised in previous rounds and did not raise the fresh capital to spend it. 

Instead, it said, it is getting ready to run as a cash-generating business that can "move and flex quickly as its business and the market evolves". 

Currently the internet company has over 9 million weekly active users, with 6 million of those accessing the platform every day.  

The announcement follows a number of others by the company that are focused on the service, including a new way to work with external groups directly in Slack called Shared Channels. 

It has also launched in multiple new languages, including French, German and Spanish, with Japanese to follow.