Dual Rank and Single Rank memory on Proliant ML30 Gen9 server.

Hi everyone, I have a Proliant ML30 Gen server whit a Intel Xeon CPU E3-1220 v5, 4GB RAM DDR4 1rx8 2113MHz UNBUFFERED ECC CL15 memory, and the server it's been running out of RAM because I'm virtualizating two machines whit Windows Server 2012 so I need more RAM and I can't find anywhere the especific 8GB RAM for this model, searching only I've found a Kingston 8GB memory KTH-PL421E/8G 8GB DDR4 2113 MHz UNBUFFERED ECC CL15, but i have a single rank memory and this i think it's dual rank; a partner recommended me to buy and install the model KTH-PL424E/8G 8GB DDR4 2400 MHz UNBUFFERED ECC CL17 but the processor doesn't support 2400MHz memory.

The question is, This server model and processor it's compatible whit dual and single rank memory?, Is it possible to work with Dual Rank and Single Rank memory simultaneously?, Can i install a 2400MHz frecuency memory and a 2133MHz whit different CAS latency? (obviously in the configuration mencionated above), Which of the two memories (KTH-PL421E/8G or KTH-PL424E/8G) recommend for this model?

Thanks for your answers and your help.