Intramolecular Ferromagnetism in a Novel Hexanuclear (.mu.-Hydroxo)(.mu.-carbonato)copper(II) Bipyridine Complex. Structure of [Cu6(bpy)10(.mu.-CO3)2(.mu.-OH)2](ClO4)6.cntdot.4H2O and of a Dinuclear .mu.-Carbonato Complex [Cu2(bpy)4(.mu.-CO3)](PF6)2.cntdot.2DMF