Maw-Cherng Suen

Adjusting the frameworks of polymeric silver(I) complexes with 2-aminopyrimidyl ligands by changing the counterions

The complexes [Ag2(L)2(SO4)]∞, (L = 2-aminopyrimidine) 1, [Ag(L)1.5(ClO4)]∞, 2, and [Ag(L)(OAc)·2H2O]∞, 3, were prepared by layering the aqueous solution of the corresponding Ag(I) salt with L in ethanol, while [Ag(L′)(NO3)]∞, 4, and [Ag(L′)(ClO4)·H2O]∞, 5, were prepared by refluxing AgNO3 and AgClO4, respectively, with 2-amino-4,6-dimethylpyrimidine (L′) in H2O. Reaction of Ag2SO4 with L′ in methanol afforded the complex [Ag4(L′)2(SO4)2(H2O)4]∞, 6. In complex 1, the L ligands are coordinated to the Ag(I) metal centers in new tridentate fashions, forming 2-D pleated molecular sheets which are interlinked by the SO42− anions to form a 3-D layer structure. Complex 2 forms a pleated molecular sheet consisting of twenty four-membered metallocycles, involving six Ag ions which are bridged by six L ligands through the pyrimidyl nitrogen atoms. Complex 3 forms linear chains with sinusoidal geometry, which are interlinked through extensive Ag⋯Ag interactions (Ag⋯Ag = 3.102 A) to form 2-D wavy rectangular grids. Complex 4 forms single-strained helical coordination polymers, which are interlinked through a series of Ag⋯O interactions (2.667 and 2.699 A) to form 2-D chair like grids. The silver atoms of 5 are bound to the nitrogen atoms of two symmetry-related L′ ligands in a distinctly non-linear geometry, forming zigzag chains. The structure of 6 consists of clusters of the formula [Ag8(L′)4(SO4)4(H2O)8], which are interlinked through L′ ligands to form 2-D sheets. The μ1-O, μ2-O′- bonding mode of the SO42− anion in complex 6 is unique for Ag(I) complexes. Their thermal properties have been investigated by using differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA)

One-dimensional structures of zinc(II) and cobalt(II) coordination complexes [Zn(NCS)2(PPz)]n and [CoCl2(PPz)]n (PPz = piperazine)

Abstract The reaction of Zn(NO3)2·6H2O with PPz hexahydrate (PPz=piperazine) and NH4SCN in CH3OH afforded the complex [Zn(NCS)2(PPz)]n (1). The reaction of CoCl2·6H2O with PPz in CH3OH afforded the complex [CoCl2(PPz)]n (2). The PPz ligand in 1 is coordinated to the metal centers through both nitrogen atoms to form a 1-D zigzag-chain structure and the distorted tetrahedral coordination geometry at each zinc center is completed by a pair of N-bonded thiocyanate ligands. Compound 2 has an analogous 1-D zigzag-chain structure containing terminal chloro ligands. Important NCS⋯HN hydrogen-bonding interactions in compound 1 and NH⋯ClM and CH⋯ClM hydrogen-bonding interactions in compound 2 play a significant role in aligning the polymer strands in the crystalline solid.

Dimolybdenum complexes of bis(2-pyridyl)amine (Hdpa) ligand and its anion (dpa−); transformation of chelating η2-Hdpa to bridging η2-dpa−

Abstract The reaction of trans-Mo2(O2CCR3)2X2(PPh3)2 with 1 equiv. of Hdpa (Hdpa=bis(2-pyridyl)amine) in CH2Cl2 afforded the complex cis-Mo2(O2CCR3)2X2(η2-Hdpa) (R=H, X=Cl, 1; R=H, X=Br, 2; R=F, X=Cl, 3, R=F, X=Br, 4). Layering of a Mo2(O2CCF3)4 solution in CH2Cl2 with Hdpa in ether produced red and yellow crystals, which were characterized as Mo2(η2-dpa)4 (5), and Mo2(O2CCF3)4(η1-HO2CCF3)2 · 2Hdpa (6), respectively. Complex 5 can also be prepared by reaction of trans-Mo2(O2CCR3)2X2(PPh3)2 with excess Hdpa. Their UV–Vis and IR spectra have been recorded and the structures of 4, 5 and 6 have been determined. The Hdpa ligand in 4 is coordinated to the metal centers via two terminal pyridine nitrogen atoms with a cis-N conformation. The dpa− ligands in 5 are bridged to the metal centers via one terminal nitrogen atom and the central nitrogen atom. The aligned-N conformation of the dpa− ligand is stabilized by both the intramolecular Mo⋯N and C–H⋯N interactions. In 6, the CF3COOH ligands coordinate to the metal centers in the axial positions with η1-bonding modes and the Hdpa molecules adapt cis-N conformations.

Synthesis and X-ray structures of some Group 6 metal carbonyl bis(2-pyridyl)formamidine complexes

New complexes of the types M(CO) 4 (HDpyF) (M=Cr, 1 ; M=W, 2 ) and Mo(CO) 3 (HDpyF)(CH 3 CN) ( 3 ), have been prepared by the reactions of bis(2-pyridyl)formamidine (HDpyF) with corresponding Group 6 metal hexacarbonyls in THF and CH 3 CN, respectively. The HDpyF ligands in complexes 1 – 3 coordinate to the metal centers in novel bidentate fashions but in different bonding modes. All the three complexes show supramolecular structures in the solid state by intermolecular hydrogen bonding and aromatic π–π stacking interactions.

Novel cyclic hexanuclear complexes containing quadruply bonded units joined by µ6-carbonate ions

Three complexes {[trans-Mo2(O2CCF3)2(µ-dppa)]3(µ6-CO3)(µ2-X)3}F [X = Cl, Br or I; dppa = N,N-bis(diphenylphosphino)amine], are reported, which are the first cyclic, hexanuclear complexes containing quadruply bonded units joined by carbonate ions.

Chemistry of dimolybdenum complexes containing anions of N,N′-di(6-methyl-2-pyridyl)formamidine (HDMepyF) and carboxylate ligands

Abstract Reactions of Mo2(O2CCF3)4 and Mo2(O2C(CH2)nCH3)4 with N,N′-di(6-methyl-2-pyridyl)formamidine (HDMepyF) in CH2Cl2 afforded complexes of the types Mo2(O2CCF3)2(DMepyF)2, 1, and Mo2(O2C(CH2)nCH3)2(DMepyF)2 (n=0, 2; n=2, 3; n=5, 4; n=8, 5; n=14, 6), respectively. Their structures have been determined by X-ray crystallography. The molecular structures of complexes 1–6 consist of two quadruply bonded molybdenum atoms, which are spanned by two trans bridging formamidinate ligands and two trans bridging carboxylate ligands. The formamidinate ligands are coordinated to the Mo centers in bidentate fashions via the two central nitrogen atoms and the two terminal pyridyl rings are dangling. The DMepyF− ligand adopts the s-cis, s-trans-conformation, resulting in a Mo⋯N and a Mo⋯HC short distances. Complex 6 is the first structurally characterized dimolybdenum complex containing carboxylate ligands with the longest alkyl chains.

Optical activity of dimolybdenum complex induced by chiral, chelating diamine ligand; syntheses and structures of [Mo2(O2CCF3)2(S,S-dach)2(CH3CN)2][BF4]2 and [Mo2(O2CCF3)2(R,R-dach)2(CH3CN)2][BF4]2 (dach=1,2-diaminocyclohexane)

Abstract The first structurally characterized, quadruply bonded complexes containing chiral diamine ligands, [Mo2(O2CCF3)2(S,S-dach)2(CH3CN)2][BF4]2 (1), and [Mo2(O2CCF3)2(R,R-dach)2(CH3CN)2][BF4]2 (2); (dach=1,2-diaminocyclohexane) were prepared by reactions of [Mo2(O2CCF3)2(CH3CN)6][BF4]2 with S,S-dach and R,R-dach, respectively, in CH3CN. Their UV–Vis and circular dichroism (CD) spectra have been recorded and their structures determined by X-ray crystallography. Crystals of complexes 1 and 2 conform to the space groups P2 with two independent half molecules in the asymmetric unit. The two molecules have a similar structure consisting of a Mo2 unit bridged by two cis-trifluoroacetate ligands and chelated by two dach ligands. Two acetonitrile molecules are coordinated to the Mo centers along the MoMo bond. The absorption wavelength at 507 nm for both 1 and 2 can be assigned to δxy→δxy* transitions. The solution CD spectra of these two complexes show two prominent bands at 525 and 385 nm and form mirror images of each other. The solid CD spectra of complexes 1 and 2 show marked red-shift in the absorption energies as compared with those measured in solution. The one-electron static coupling mechanism was invoked to explain the CD spectra for these complexes and the second lowest energy bands were assigned to be δxy→δx2−y2 transitions.