Text format value for SharePoint Date and Time column

I've got a Date and Time column in SharePoint and I try to assign value to it using SOAP API. However column is not updated and shows default value. Assuming that I have no problems with other column types, I suppose that I just write value in incorrect format. So my question is - what correct format should be?

P.S. I write date and time in this format: YYYY-MM-DDTHH:MM:SS ( in example "2014-07-30T16:54:55" ), all dates are in datetime sql format limits.