Synthesis, X-ray crystal structures, magnetism, and phosphate ester cleavage properties of copper(II) complexes of N-substituted derivatives of 1,4,7-triazacyclononane.
Two new N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle, 1-benzyl-4,7-dimethyl-1,4,7-triazacyclononane (L2) and 1,4,7-tris(3-cyanobenzyl)-1,4,7-triazacyclononane (L3), have been prepared and, together with 1,4-dimethyl-1,4,7-triazacyclononane (L1), have been used to synthesize the corresponding hydroxo-bridged binuclear copper (II) complexes, [Cu2(mu-OH)2L2](ClO4)2.xH2O (1 L = L1, x = 0; 2 L = L2, x = 1; 3 L = L3, x = 2). The X-ray crystal structures of all three complexes reveal the presence of [Cu2(mu-OH)2]2+ cores capped by pairs of facially coordinating tacn ligands so that the Cu(II) centers reside in distorted square pyramidal coordination environments. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -36.4 cm(-1)) between the Cu(II) centers in 1, while the centers in 2 and 3 have been shown to interact ferromagnetically (J = 11.2 and 49.3 cm(-1), respectively). The variation in the strength and sign of these interactions has been rationalized in terms of the differing geometries of the [Cu2(mu-OH)2]2+ cores. The ability of the Cu(II) complexes to cleave phosphate ester bonds has been probed using the model phosphate ester bis(4-nitrophenyl)phosphate (BNPP) at pH 7.4 and a temperature of 50 degrees C. The measured rate constant for 3 (3 x 10(-4) s(-1)) is significantly greater than those previously reported for the Cu(II) complexes of the fully alkylated tacn ligands, Me3tacn and iPr3tacn, which until now have been rated as the most effective tacn-based phosphate ester cleavage agents.
Belousoff
Matthew J
MJ
School of Chemistry, Monash University, Victoria, 3800, Australia.
Duriska
Martin B
MB
Graham
Bim
B
Batten
Stuart R
SR
Moubaraki
Boujemaa
B
Murray
Keith S
KS
Spiccia
Leone
L
D040761:Biomimetic Materials / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008280:Magnetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010755:Organophosphates / Q000737:chemistry*; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry
D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; D010755:Organophosphates; C075712:1,4,7-triazacyclononane; D003300:Copper; D010744:Phosphoric Monoester Hydrolases