Each of the 
arrangements can be extended, to ALMOST tile the plane by themselves. Maybe one of the arrangements has no gap, I don’t know. Here’s the 7×7 version extended, and detail of the centre:
Each of the arrangements can be extended, to ALMOST tile the plane by themselves. Maybe one of the arrangements has no gap, I don’t know. Here’s the 7×7 version extended, and detail of the centre: