In LibreOffice Math, can brackets be shown separately so that the distance between them is freely definable?
You can set individual brackets using "left" and "right", but the distance between the brackets will not be fixed, as they adapt to the argument. Nevertheless, there is a way to display brackets so that the distance between them is fixed. To accomplish this, place a "\" (backslash) before the normal brackets. These brackets now behave like any other symbol and the alignment is the same as with other symbols:
left lbrace x right none
size *2 langle x rangle
size *2 \langle x \rangle