CONFORMATIONAL CHANGE OF THE N,N'-BIS(3-AMINOPROPYL)OXAMIDATE LIGAND IN NUCLEARITY TAILORING COPPER(II) COMPLEXES

N,N'-Bis(3-aminopropyl)oxamide (H(2)L(1)) which can adopt cis and tran s conformations reacted with copper(rr) salts in its deprotonated form to yield the compounds [CuL(1)] 1, [Cu(3)L(2)(1) (NO3)(2)]. H2O 2, [C u(2)L(1)(NO3)(2)] 3 and [Cu(2)L(1)(O(2)CMe)(2)]. 2H(2)O 4. The structu res of 1, 3 and 4 have been determined by single-crystal X-ray diffrac tion methods. That of 1 consists of mononuclear [CuL(1)] units where t he oxamidate is in a cis conformation co-ordinated to the copper atom through its four nitrogen atoms. The copper surroundings are close to square planar. The amidate-copper bond distance [1.955(6) Angstrom] is significantly Shorter than that involving the amine group [1.999(7) A ngstrom]. The structures of 3 and 4 comprise centrosymmetric trans oxa midate-bridged copper(II) dinuclear units which are linked by asymmetr ic bis(monodentate) nitrate (3) and acetate (4) ligands to yield a She et-like polymer (3) and an alternating chain (4). The co-ordination ge ometry around each copper atom is distorted square pyramidal: the equa torial plane comprises the oxygen and nitrogen atoms of the amide, the nitrogen atom of the amine group and an oxygen atom from nitrate (3) or acetate (4) ligands. The apical position is filled by an oxygen ato m from another nitrate (3) or acetate (4) group. The copper-copper sep arations across the oxamidate are 5.190(1) and 5.244(1) Angstrom for 3 and 4, respectively, and those across the nitrate and acetato groups are 5.116(1) and 3.350(1) Angstrom. Variable-temperature magnetic susc eptibility measurements show a Curie law behaviour for 1 and the occur rence of a strong antiferromagnetic coupling through the oxamidate bri dge in 2-4 (J = -325, -393 and -305 cm(-1), respectively). The versati lity of L(1) as a ligand and its ability to mediate strong antiferroma gnetic interactions is analysed and discussed.