Structural Systematics of Rare Earth Complexes. XVII Hydrated 1 : 1 Adducts of 2,2′:6′,2″-Terpyridine with the Lanthanoid(III) Bromides and Some Binuclear Hydroxy-Bridged Dimers

Abstract

Room-temperature single-crystal X-ray structural characterizations are recorded for hydrated lan- thanoid(III) bromide/2,2′:6′,2″-terpyridine (tpy) (1 : 1) complexes, showing all to be ionic and of the form [(tpy)Ln(OH₂)x]Br₃.yH₂O, where x and y are 6 and 1 for the isomorphous series Ln = La(-)Er (and intermediate members, by presumption), and 5 and various values for Ln = Tm, Yb, Lu. Crystals of [(tpy)Ln(OH₂)₆]Br₃.H²O are monoclinic, P 2₁/c, a ≈ 8·5, b ≈ 18, c ≈ 16·3 Å, β ≈ 108°, Z = 4; for Ln = La, Er, conventional R values on |F| were 0·048, 0·080 for N_o 4027, 1347 ‘observed’ (I > 3σ(I)) diffractometer reflections respectively. The complex [(tpy)Tm(OH₂)₅]Br₃.H₂O is monoclinic, P 2₁/c, a 8·506(4), b 17·376(1), c 15·951(6) Å, β 106·87(3)°, Z = 4, (quasi-)isomorphous with the Ln = La-Er array, R 0·065 for N_o 2067. [(tpy)Yb(OH₂)₅]Br₃.4H₂O is triclinic, P 1, a 11·902(2), b 11·639(3), c 9·831(2) Å, α 98·92(2), β 106·84(2), γ 92·42(2)°, Z = 2, R 0·062 for N_o 3422, while [(tpy)Lu(OH₂)₅]Br₃.H₂O is monoclinic, P 21/n, a 13·635(8), b 9·022(5), c 19·03(1) Å, β 99·02(5)°, Z = 4, R 0·043 for N_o 3139. Despite a common N₃LnO₅ coordination sphere in the last three compounds, subtle differences are found in stereochemistry; in the N₃LnO₆ array, one of the outer water molecules becomes progressively detached as the lanthanoid radius contracts. Some tendency is found toward the end of the lanthanoid series toward the formation of di(hydroxy-bridged) neutral dimers, Ln(OH)Br₂/tpy/H₂O(1 : 1 : 8)(×2), [(tpy)(H₂O)₃Ln(µ-OH)₂Ln(OH₂)₃(tpy)]Br₄.10H₂O, monoclinic, C 2/c, a ≈ 19·5, b ≈ 14·5, c ≈ 17·1 Å, β ≈ 92°, Z = 4 dimers, thus far defined by full determinations for the extrema Lu = Er, Lu (and Y), R 0·055, 0·043, (0·047) for N_o 3141, 4591, (2991) respectively; the dimer is disposed about a crystallographic 2 -axis. An Ln = Dy example, seemingly isomorphous, has also been characterized by cell determination.