Map Control-Shift-Tab in rxvt-unicode

I've got S-Tab working with this :

URxvt.keysym.C-Tab: \033{
URxvt.keysym.Control-Shift-ISO_Left_Tab: \033} 
! disable ctrl-shift
URxvt*iso14755: False 
URxvt*iso14755_52: False

and in vim I have

nmap ^[{ :tabnext<cr>
imap ^[{ <ESC>:tabnext<cr>
nmap ^[} :tabprevious<cr>
imap ^[} <ESC>:tabprevious<cr>

Shift+Tab is often mapped to the ISO_Left_Tab keysym in X11, so some programs may need this instead of a literal 'shift-tab' in their configuration.

urxvt has a strange mapping on ctrl+shift, it looks like you will have to recompile to disable it: see this page for more details. EDIT It looks like in recent versions of rxvt you can simply add

URxvt.iso14755_52: False