The Complexing Properties of 1-Aminosquarate Derivatives with Lead

Reaction of three different 1-(dialkylamino) derivatives of 3,4-dihydroxycyclobut-3-ene-1,2-dione (squaric acid) with lead(II) nitrate in aqueous solution yielded polymeric complexes which have been characterized by single-crystal X-ray analysis. Pb[(CH(3))(2)NC(4)O(3)](2)(OH(2))(2).H(2)O (1) produced from 1-(dimethylamino)-2-methoxycyclobutenedione crystallizes in the triclinic space group P&onemacr;, with a = 8.591(5) Å,b = 9.308(4) Å, c = 10.571(4) Å, alpha = 95.58(2) degrees, beta = 94.96(3) degrees, gamma = 95.78(4) degrees, and Z = 2. The complex of formula Pb[(C(2)H(5))(2)NC(4)O(3)](2)(H(2)O) (2) formed from the corresponding 1-(diethylamino) analogue of the ligand also crystallizes in space group P&onemacr;, with a = 7.521(2) Å, b = 10.928(4) Å, c = 11.749(4) Å, alpha = 90.10(2) degrees, beta = 97.84(2) degrees, gamma = 95.12(2) degrees, and Z = 2. In both of these complexes, the lead atom is eight-coordinate with the ligands being bound in bidentate and binucleating fashions. The di-n-propylamino substituent in the di-n-propyl homologue hydrolyzed during crystallization, and a lead(II) squarate, Pb(C(4)O(4))(H(2)O)(4) (3), was produced: monoclinic space group P2(1), with a = 6.466(2) Å, b = 7.898(3) Å, c= 8.307(3) Å, beta = 92.88(3) degrees, and Z = 2. The lead atom is again eight-coordinate, and the squarate moiety, bidentate and binucleating. The respective coordination polyhedra for the complexes are square antiprismatic (1), bicapped trigonal prismatic (2), and distorted mono faced-capped and edge-capped trigonal prismatic (3).