Save yourself the money and buy 2133mhz. It could cause problems to where it may not read the ram at times or cause other issues you're better off to stick with what your mobo is recommended to avoid any issues at all.
2133Mhz is the JEDEC standard speed for DDR4. It's literally the lowest speed you can have as a standard setting in any DDR4 motherboard and any lower requires manually changing it in bios if that is supported. Any DDR4 module added to a motherboard will always be set to 2133Mhz unless it is advertised to automatically clock to 2400-2666Mhz without adjusting it in bios. Any module advertised for over 2666Mhz will start at 2133Mhz until you set the XMP for it's advertised speed. Edit - Also, Any module that should automatically overclock to 2400-2666Mhz placed in a motherboard that only supports 2133Mhz, or is limited by the CPU to 2133Mhz, will always set to 2133Mhz.