ACR Y DSCNT TO OCCUPIED ALT HAD LTSS FROM ACR X. SYS ERROR.

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I WAS THE RADAR CTLR AT SECTOR 60 IN ZDC. THIS SECTOR OWNS THE ALTS OF 17000 FT; FL270. THE SECTOR IS DESIGNED AS TRANSITION SECTOR TO CLB DCA; IAD AND BWI SBOUND DEPS INTO THE ENRTE ENVIRONMENT. HOWEVER; AT THE TIME OF THE INCIDENT; ACFT THROUGHOUT THE AREA WERE ENCOUNTERING MODERATE TURB ABOVE FL220. THEREFORE MOST PLTS WERE ANXIOUS TO DSND TO THESE LOWER ALTS WHICH CAUSED SEVERAL ENRTE ACFT TO BE FLYING THROUGH THIS TRANSITIONAL SECTOR. I ACCEPTED HDOFS ON ACR X AT FL240 AND ACR Y AT FL260 IN CLOSE LATERAL PROX TO EACH OTHER. BOTH PLTS WERE REQUESTING LOWER DUE TO TURB. I WAS ANXIOUS TO COMPLY AND GAVE Y FL250. WASHINGTON APCH OWNED THE AIRSPACE AT AND BELOW FL230 WHERE THIS ACFT WAS. I COORDINATED LOWER FOR BOTH ACFT WITH DCA APCH. I THEN INADVERTENTLY DSNDED Y TO FL240 BEFORE DSNDING X AND STANDARD SEPARATION WAS LOST. I BELIEVE I MADE THIS ERROR BECAUSE OF MY ANXIOUSNESS TO ASSIST BOTH PLTS. SEVERAL PLTS WERE COMPLAINING OF THE RIDES WHICH HINDERS THE OP. THE SOONER YOU STOP THEIR COMPLAINTS; THE BETTER OFF YOU ARE AS A CTLR.