Synthesis and solution properties of lanthanum(III), europium(III), and lutetium(III) THP complexes and an x-ray diffraction study of a crystal containing four stereoisomers of a europium(III) THP complex (THP = 1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane). Methyl groups impart rigidity to S,S,S,S-THP macrocyclic complexes