Here is the link for NUC technical specifications.
Read section 1.4 on page 21 carefully: https://www.intel.com/content/dam/support/us/en/documents/boardsandkits/NUC7i5BN_NUC7i7BN_TechProdSpec.pdf
Do NOT use 2400 MHz memory.
Actually I tried DDR4 2133x2, DDR4 2400x2, DDR4 2666x2, and one DDR4 2133 + one DDR4 2400 on my NUC 7i3, they all worked perfectly. If the rated DIMM clock is higher than 2133MHz, it will automatically drop to 2133 without any issue.
There are 288 pins for DDR4 desktop memories and 260 pins for laptop modules, so you cannot use your 288-pin memories on an Intel NUC 'cause NUC needs laptop memories.