Visa requirements do not have anything to do with 2 separate tickets. You can TWOV (Travel Without Visa) if you are in Transit to another international destination from the International Sterile Zone. You need a Visa when you will be leaving that zone.
See below current visa requirements if you wanted to use this and a separate ticket to go to Israel.
So your connecting flight needs to be from SVO and needs to leave within 24 hours. If you meet those requirements no VISA is required.
Happy travels.
TIMATIC-3 / 24FEB15 / 1751 UTC
NATIONAL USA (US) /TRANSIT RUSSIAN FED. (RU)
DESTINATION ISRAEL (IL)
ALSO CHECK DESTINATION INFORMATION BELOW
VISA TRANSIT RUSSIAN FED. (RU)
...... NORMAL PASSPORTS ONLY ......
TWOV (TRANSIT WITHOUT VISA):
VISA REQUIRED, EXCEPT FOR HOLDERS OF ONWARD TICKETS FOR A MAX.
TRANSIT >TIRULES/R32 TIME OF 24 HOURS.
- TWOV NOT APPLICABLE IF TRANSIT IS TO/FROM BELARUS.
- THERE ARE NO TRANSIT FACILITIES AVAILABLE AT KHABAROVSK
(KHV), KRASNODAR (KRR), YUZHNO SAKHALINSK (UUS) AND
VLADIVOSTOK (VVO). PASSENGERS ARE REQUIRED TO CLEAR
IMMIGRATION AND CUSTOMS.
- IF IN TRANSIT TO/FROM BELARUS; OR IF THE AIRPORT OF ARRIVAL
IS DIFFERENT FROM THE AIRPORT OF DEPARTURE WITHIN THE SAME
RUSSIAN CITY, THEN A RUSSIAN (TRANSIT) VISA IS REQUIRED.