LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. OPERATIONAL ERROR.

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I WAS WORKING JBR LO; A DEP SECTOR FROM MEM. JBR LO AND FCY LO WERE COMBINED; AND THERE WERE TSTMS IN THE AREA. I WAS WORKING APPROX 15 DEPS FROM MEM AND SEVERAL OTHER ACFT. ACR X DEPARTED LITTLE ROCK AND I CLBED HIM TO FL230 ON A 050 DEG HDG. SHORTLY AFTER THIS ACR Y WAS POINTED OUT TO ME AS DEVIATING ON A 300 DEG HDG. I APPROVED A POINTOUT ON THAT HDG CLBING TO FL230. APPROX 2 MINS LATER I WAS INFORMED THAT Y WAS GOING TO DEVIATE ON A 260 DEG HDG. I ADVISED RADAR CONTACT IN ORDER TO WORK THE ACFT. WHEN I ESTABLISHED COM WITH Y I STOPPED HIM AT FL210. AT THIS TIME BOTH ACFT WERE LEAVING FL200. I ALSO TOLD Y TO FLY HDG 270 DEGS. AFTER SEVERAL OTHER XMISSIONS I TOLD ACR X TO EXPEDITE CLB THROUGH FL220. ACR Y REQUESTED TO TURN LEFT 'RIGHT NOW' DUE TO WX. I APPROVED THIS THINKING X WOULD TOP Y. WHEN I SAW THIS WOULD NOT WORK I ATTEMPTED TO VECTOR Y; BUT THE PLT WOULD NOT ANSWER ME. I THEN ATTEMPTED TO VECTOR X AND ALSO COULD NOT TALK TO HIM. AFTER 35 SECS I ESTABLISHED COM WITH Y; AND HE INFORMED ME HE DID NOT WANT TO TURN; BUT HE WOULD. IF HE HAD TURNED WHEN I FIRST VECTORED HIM THERE WOULD NOT HAVE BEEN AN OPERROR. HE DID HEAR ME THE FIRST TIME BECAUSE HE QUESTIONED THE HDG 35 SECS LATER; BUT BY THEN IT WAS TOO LATE.