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A series of zinc-containing heterodimetallic complexes were prepared by using the dinucleating ligand XDK [H 2 XDK ) m-xylylenediamine bis(Kemp's triacid imide)]. Mononuclear [Zn(XDK)(H 2 O)] (1) reacts with 1 equiv of M(acac) 2 ‚2H 2 O (acac ) 2,4-pentanedionate) to afford the heterodimetallic compounds [Zn II M II (XDK)(acac) 2 (CH 3 OH) 2 ]‚H 2 O (2‚H 2 O, M ) Co, 65% isolated yield; 3‚H 2 O, M ) Mn, 54%; 4‚H 2 O, M ) Fe, 30%; 5‚H 2 O, M ) Ni, 32%). As determined by X-ray crystallography, 2-5 each contain a Zn II M II dinuclear core bridged by XDK and acac ligands. The zinc and M atoms have trigonal bipyramidal and octahedral geometries, respectively. The Zn‚‚‚M separations depend on the metal ion in the octahedral site (2, M ) Co, 3.440(2) Å; 3, M ) Mn, 3.517(1) Å; 4, M ) Fe, 3.492(1) Å; 5, M ) Ni, 3.397(1) Å), a variation which is correlated with the ionic radius of the high-spin octahedral metal ion. The reaction of 2 with diphenyl hydrogen phosphate afforded the bis(phosphate) complex [ZnCo(XDK){µ-η 2 -(PhO) 2 PO 2 }{η 1 -(PhO) 2 PO 2 }(CH 3 OH) 2 (H 2 O)] (7, 49% yield). The ZnCo center is bridged by the XDK through its two carboxylate groups and by a diphenyl phosphate ligand. The other diphenyl phosphate is terminally coordinated to the zinc atom in a monodentate fashion. The Zn‚‚‚Co interatomic distance is 3.846 (1) Å. An analogous bis(phosphate) homodinuclear complex, [Zn 2 (XDK){µ-η 2 -(PhO) 2 PO 2 }{η 1 -(PhO) 2 PO 2 }(CH 3 OH) 2 (H 2 O)] (8), was prepared by reacting [Zn 2 (XDK)(acac) 2 (CH 3 OH) 2 ] (6) with diphenyl hydrogen phosphate in 64% yield. Compound 8, which is isomorphous with 7, has an asymmetrical dizinc core bridged by XDK and a phosphate ligand (Zn‚‚‚Zn ) 3.869(2) Å). The monodentate diphenyl phosphate ligand dissociates from the dimetallic center of 8 in solution, as revealed by molar conductivity and 1 H and 31 P{ 1 H} NMR spectroscopic studies. The resulting free phosphate ligand exchanges with the bridging one in methanol-d 4 . The present results provide a useful synthetic route to carboxylate-bridged heterodimetallic compounds, which are potential models for the active centers in nonredox metalloproteins. Crystal data are as follows. 2: monoclinic, P2 1 /c, a ) 17.725 (7) Å, b ) 12.354(4) Å, c ) 21.815(6) Å, ) 90.45(3)°, V ) 4777(2) Å 3 , Z ) 4; R ) 0.049 and R w ) 0.051 for 3884 reflections with I > 3σ(I). 3: monoclinic, P2 1 /c, a ) 17.292(2) Å, b ) 12.450(1) Å, c ) 21.717(2) Å, ) 91.464(7)°, V ) 4673.9(7) Å 3 , Z ) 4; R ) 0.046 and R w ) 0.051 for 3876 reflections. 4: monoclinic, P2 1 /c, a ) 17.630(1) Å, b ) 12.374(2) Å, c ) 21.771(2) Å, ) 90.306(8)°, V ) 4749.4(7) Å 3 , Z ) 4; R ) 0.041 and R w ) 0.049 for 3248 reflections. 5: monoclinic, P2 1 /c, a ) 17.817(2) Å, b ) 12.241(3) Å, c ) 21.786(2) Å, ) 91.043(9)°, V ) 4751(1) Å 3 , Z ) 4; R ) 0.050 and R w ) 0.058 for 4497 reflections. 7‚CH 3 OH: monoclinic, P2 1 /n, a ) 18.812(2) Å, b ) 16.156(2) Å, c ) 21.760(2) Å, ) 112.836(9)°, V ) 6095(1) Å 3 , Z ) 4; R ) 0.055 and R w ) 0.064 for 5843 reflections. 8‚CH 3 OH: monoclinic,...

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Carboxylate-bridged dimagnesium(II) complexes were synthesized and characterized by employing the dinucleating ligand XDK, where H 2 XDK is m-xylylenediamine bis(Kemp's triacid imide). The reaction of 1 or 2 equiv of sodium diphenyl phosphate with [Mg 2 (XDK)(CH 3 OH) 4 (H 2 O) 2 (NO 3 )](NO 3 ), 1(NO 3 ), afforded [Mg 2 (XDK){µ-η 2 -(PhO) 2 PO 2 }(CH 3 OH) 3 (H 2 O)(NO 3 )]‚3CH 3 OH (2‚3CH 3 OH) and [Mg 2 (XDK){µ-η 2 -(PhO) 2 PO 2 }{η 1 -(PhO) 2 PO 2 }(CH 3 -OH) 3 (H 2 O)]‚CH 3 OH (3‚CH 3 OH), respectively. These are the first structurally characterized phosphate esterbridged dimagnesium(II) complexes. The reaction of 1 with 1 equiv of bis(4-nitrophenyl) hydrogen phosphate resulted in protonation of one of the carboxylate ligands and liberation of one magnesium(II) ion to give [Mg-(HXDK) 2 (H 2 O) 2 ] (4), an octahedral complex containing two short, low barrier intramolecular OH‚‚‚O hydrogen bonds. The phosphate ester exchange rate of free and bound diphenyl phosphate in 3 in methanol solution was measured by variable-temperature 31 P{ 1 H} NMR spectroscopy and compared to that of structurally analogous dizinc(II), [Zn 2 (XDK){µ-η 2 -(PhO) 2 PO 2 }{η 1 -(PhO) 2 PO 2 }(CH 3 OH) 2 (H 2 O)] (5), and dicalcium(II), [Ca 2 (XDK){µ-η 2 -(PhO) 2 PO 2 }{η 1 -(PhO) 2 PO 2 }(CH 3 OH) 3 (H 2 O)]‚CH 3 OH, (6‚CH 3 OH), complexes. The synthesis and structural characterization of 6 is presented, along with a discussion of the differences between the carboxylate-and phosphate ester-bridged dimagnesium(II), dizinc(II), and dicalcium(II) centers. Crystallographic data are as follows. 1(NO 3 ): monoclinic, P2 1 /c, a ) 11.240(3) Å, b ) 13.019(2) Å, c ) 30.208(7) Å, ) 99.11(1)°, V ) 4365(2) Å 3 , Z ) 4, R ) 0.045, and R w ) 0.054 for 5021 independent reflections with I > 3σ(I). 2‚3CH 3 OH: monoclinic, P2 1 /c, a ) 16.611(5) Å, b ) 16.059(6) Å, c ) 21.930(9) Å, ) 93.34(6)°, V ) 5840(4) Å 3 , Z ) 4, R ) 0.069, and R w ) 0.085 for 3759 independent reflections with I > 2σ(I). 3 . CH 3 OH: monoclinic, P2 1 /n, a ) 18.912(4) Å, b ) 16.254(2) Å, c ) 21.646(5) Å, ) 112.26(2)°, V ) 6158(2) Å 3 , Z ) 4, R ) 0.060, and R w ) 0.072 for 5184 independent reflections with I > 3σ(I). 4: monoclinic, P2 1 /n, a ) 15.210(5) Å, b ) 15.772(3) Å, c ) 13.093(3) Å, ) 96.35(3)°, V ) 3122(1) Å 3 , Z ) 2, R ) 0.069, and R w ) 0.070 for 1840 independent reflections with I > 2σ(I). 6 . CH 3 OH: monoclinic, P2 1 /n, a ) 16.5471(3) Å, b ) 24.3415(6) Å, c ) 16.5865(3) Å, ) 104.2530(10)°, V ) 6475.