A series of heavy lanthanide(III) and yttrium(III) monoporphyrinato complexes formulated in [Ln(TPP)(cyclen)]Cl (Ln = Tb, Dy, Ho, Er, Tm, Yb, and Y; TPP = 5,10,15,20-tetraphenylporphyrinato), with cyclen, 1,4,7,10-tetraazacyclododecane, as a capping ligand, have been prepared in mild conditions and studied using single-crystal X-ray diffraction crystallography. The complexes exhibit an electronic absorption band (B(0,0)) in the range of 421-423 nm, showing a bathochromic shift associated with the increase of the ionic radii of the lanthanide, as well as two peaks of Q(1,0) and Q(0,0) bands between 548-586 nm. All of the complexes are isostructural, where both TPP and cyclen are coordinated to a lanthanide(III) or yttrium(III) ion giving an eight-coordinate square-antiprismatic (SAP) geometry (average skew angles are in the range of 43.01°-43.67°). The mean plane of the four nitrogen atoms of TPP (N) and that of the cyclen (N) are virtually parallel with a dihedral angle of less than 1°. The lanthanide(III) or yttrium(III) ions lie between N and N. The position of the metal ion is closer to the N plane, which is presumably caused by the different charges of the ligands, the size of the N square ligands, and the steric factor. The average Ln-N and interplanar distances (d) decrease with decreasing lanthanide(III) ionic radii, showing the effect of lanthanide contraction. The skew angles, opening angles, and N-N distances are nearly unchanged, keeping the rigid square antiprismatic geometry throughout the series.
