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45 across. polygonal structure provided by us money: church with more people and energy, not half . 20 letters
7 down. something wrong I wander endlessly left, not right . 9 letters

many thanks in advance

buckminsterfullerene?

buck = money,
minster = church

I think 45 ad is BUCKMINSTERFULLERENE - it's a form of carbon with a molecular structure reminiscent of the geodesic dome
7d could be SINISTRAL, but don't ask me about the parsing

sin i stra[y] L.

45 Across

After BUCK (US Money) and MINSTER (church) it's FULLER (with more people) and ENE(rgy) not half

Last one. I know I'm going to kick myself.

52d On trip for school (4)

?0?H

HIGH (on drugs / high school)

Thanks Brackendale. That makes my 55a wrong, which makes me doubt my 43 down.

clues for 55a? 43d?

TRICKLING = moving in little stream

Catch = TRICK
Fish = LING