LANTHANIDE TETRAMETHOXYBORATE COMPLEXES ISOLATED FROM REDUCTIVE AMINATION OF 2,6-DIFORMYL-P-CRESOL

Treatment of a hot methanolic solution of 2,6-diformyl-p-cresol (1 mmo l), 3,6-dioxa-1,8-octanediamine (2 mmol), and a lanthanide(III) nitrat e (I mmol) with sodium cyanotrihydroborate (1.5 mmol) unexpectedly yie lds a mixture of isostructural but totally different compounds, [Ln(B( OCH3)4)(NO3)2(CH3OH)2], and an asymmetric Schiff base complex, Ln25(NO 3)4.1.2CH3OH. The lanthanum complex of the B(OCH3)4- anion crystallize s in the monoclinic system, C2/c, with a = 16.50(6) angstrom, b = 6.5( 2) angstrom, c = 15.84(6) angstrom, beta = 106.8(1)-degrees, V = 1621( 2) angstrom3, and Z = 4. With 1566 unique and 1374 observed (I > 3sigm a(I)) data and 101 variables, R = 0.017 and R(w) = 0.025. The structur e features an assembly of [La(B(OCH3)4)(NO3)2(CH3OH)2]n chains in whic h La3+ ions are bridged by bidentate B(OCH3)4-anions which are distort ed noticeably from T(d) symmetry. The shortest La-O distances in the C 2v 10-fold 4A,6B-extended dodecahodral coordination polyhedron (two bi dentate NO3-, two methanol molecules, and two bidentate B(OCH3)4-) inv olve the two B(OCH3)4- anions. The B(OCH3)4- anions form strong bonds with Ln3+ cations and can achieve the geometrical distortions required for constituting the irregular Ln3+ coordination polyhedra. As good c ompetitors for Ln3+ cations, B(OCH3)4- anions can be expected to have destabilizing effects on Schiff base chelates which depend on coordina tion to Ln3+ cations to achieve stability. The structure of the Pr25(N O3)4.1.2CH3OH complex is reported elsewhere.