stm32f7x2Rx vcap1 finding a suitable low ESR capacitor
Summary:


The VCAP powers the Core. Hence, the core frequency matters other than system frequency
Connecting two 2.2uF capacitors in parallel also helps in reducing ESR because the ESR will be half of the individual parts.
A win win situation. you can either mount one 4.7 uF or two 2.2 uF sharing same copper pads.
4.7uF capacitors options are mentioned below




If I have to stick to MLCC only (I also prefer it always over tantalum), here are a few parts which I find best due to


The products are in production
The ESR is well with in 100 m Ohms
Package is 0603 and 
Several voltage options are available 10V, 16V, 25V 
I can also mount capacitors in parallel which also effectively reduces the ESR


The main frequency range to beseen will be defined by your application. Are you using PLL? Depending on peripheral and core frequency, you can have a look at the graph. I would say, it is fine.



The parts for comparison are of 4.7uF, 0603 package. Choose the capacitors which is suitable based on price and availability. Also have a look at temperature coefficient to see teh acceptable change in the capacitance over temperature range.  


  Neither of the three frequencies is within the demanded range of 0.1Ω
  and 0.2Ω... So either I'm misinterpreting something or all capacitors
  from various brands and series I looked at are unsuitable. 


For now, with the lower ESR values, the ceramic capacitors do a great job of having good response and least heat losses due to ripples. But the stability may be a topic (I am not expert in this). ESRs lower than 0.1 Ohms would be okay or may not be. You can write to ST once. Most of the regulators nowadays will be stable even with least ESR capacitors. Only ST should tell.   

By the way, the ESR is nearly 0.1 Ohms for the core clock frequency. The VCAP1 is for the core voltage regulator. I would have gone ahead with this.