The Department of Energy’s (DOE’s) Office of Science is encouraging university PI’s who currently receive financial assistance from the Office of Science to consider requesting supplemental funds to host or collaborate with students or scientists impacted by the war in Ukraine.

https://www.osti.gov/appdata/sc/UkraineDCL.pdf

The US National Academy of Sciences (NAS) has mobilized short and long term support mechanisms and welcomes financial contributions for Ukrainian scientist support. The Safe Passage Fund supports the Polish Academy of Sciences as it helps fleeing Ukrainian scholars and their families relocate to Poland and other countries. https://www.nationalacademies.org/news/2022/03/nas-launches-effort-to-help-support-ukrainian-researchers-as-they-resettle-in-poland.

International organizations, including the European Organization for Nuclear Research (CERN) have mobilized to support Ukrainian scientists https://home.cern/news/opinion/cern/cerns-response-invasion-ukraine-new-council-measures.

The US Large Hadron Collider Users Association (US LUA), established to facilitate the work of US scientists at CERN and assisted operationally by URA, offers a secure portal for donations to support the people of Ukraine. All donations are sent directly to the Office of the International Red Cross in Ukraine.
http://uslua.org/in-support-of-ukraine

Numerous grassroots organizations like Science For Ukraine and Chemistry World list opportunities for Ukrainian researchers with institutions around the world, including US institutions.