Di-μ-oxido-bis[(1,4,8,11-tetraazacyclotetradecane-κ4 N,N′,N′′,N′′′)dimanganese(III,IV)] bis(tetraphenylborate) chloride acetonitrile disolvate

The title compound, [Mn2O2(C10H24N4)2](C24H20B)2Cl·2CH3CN, is a mixed-valent MnIII/MnIV oxide-bridged manganese dimer with one chloride and two tetraphenylborate counter-anions. There are two non-coordinated molecules of acetonitrile in the formula unit. A center of inversion is present between the two metal atoms, and, consequently, there is no distinction between MnIII and MnIV metal centers. In the Mn2O2 core, the Mn—O distances are 1.817 (3) and 1.821 (3) Å. The cyclam ligand is in the cis configuration. The chloride counter-anion resides on a center of symmetry, whereas the tetraphenylborate counter-anion is in a general position. The cyclam ligand is hydrogen bonded to the acetonitrile as well as to the chloride anion. One of the phenyl rings of the anion and the acetonitrile solvent molecule are each disordered over two sets of sites.


Comment
In the title compound ( Fig. 1), the Mn III -Mn IV centrosymmetric, dinuclear cation is bridged by two oxo ligands. Each manganese atom also binds to a tetradentate cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) to achieve a distorted octahedral coordination environment. Due to the center of inversion, there is no distinction between the two different oxidation states in the structure, and it is disordered mixed valent. The dinuclear cation bears a +3 charge, and the charge is balanced by a chloride anion and two tetraphenylborate anions. The chloride resides on a center of symmetry. The configuration of the cyclam ligand is cis-V, in which the N-H bonds alternate above and below the N 4 plane (Bosnich et al., 1965).
The structures of similar disordered mixed valent (III/IV) µ-oxo bridged manganese cyclam complexes are reported in Lu, et al., 2001, with two perchlorate and one nitrate anions; Goodson, et al., 1990, with dithionate and thiosulfate anions, and a second structure with three bromides. In the title compound, the Mn 2 O 2 core has Mn-O distances of 1.817 (3) and 1.821 (3) Å. All of the above referenced structures show similar coordination geometry, and the mean Mn-O bond distances in the Mn 2 O 2 core for these complexes is 1.824 Å. A trifluoromethanesulfonate salt (Brewer, et al., 1989)  In the structure of the title compound, all of the available hydrogen atoms bonded to the N atoms in the cyclam ligand participate in hydrogen bonding ( Fig. 2 and Table 2). The hydrogen atoms bonded to N atoms N2 and N4 are hydrogen bonded to chloride atom. The hydrogen atoms on N atoms N1 and N3 hydrogen bond to the acetonitrile N atoms.

Experimental
The title compound was obtained while attempting to prepare an azido derivative. To a stirred solution of 1,4,8,11-tetraazacyclotetradecane (cyclam), (200 mg, 1 mmol) in 5 ml of methanol was added a solution of MnCl 2 . 4H 2 O (200 mg, 1 mmol) in 25 ml of methanol. Over the one hour course of the addition, the reaction color progressed from red to dark green. After stirring for 1 hr an excess of NaN 3 (200 mg, 2.5 mmol) was added to the reaction mixture in a solution of 9 ml me thanol and 1 ml H 2 O. No color change was observed upon addition of the azide. After 20 min of stirring NaBPh 4 (350 mg, 1 mmol) was added. Addition of the tetraphenylborate salt caused a precipitate to form and the solution turned red-brown. Subsequently, 18 ml of a 5:1 acetonitrile:water and 10 ml of 0.1 M HClO 4 were added. The orange-brown solid was collected by filtration.
Dichroic, red-green crystals of the product were obtained by slow evaporation of a toluene solution.

Refinement
The C-bound and N-bound H atoms were positioned geometrically with C-H = 0.95-0.98 Å, N-H = 0.88 Å, and allowed to ride on their parent atoms with U iso (H) = 1.2-1.5 U eq (C). One of the BPh 4 phenyl rings was disordered and was refined in two parts with a rigid group refinement. The acetonitrile molecule was disordered in two parts, each assigned 50% occupancy. Atoms of the disordered acetonitriles were kept isotropic. The atoms of the disordered BPh 4 phenyl group were allowed to refine with anisotropic thermal parameters and a similarity restraint (SIMU) of 0.008. The cation displayed large thermal motion and thermal ellipsoids for these atoms were refined with an ISOR 0.01 restraint. An attempt was made to solve and refine the structure in the non-centrosymmetric space group P1 but atoms of the cation became N.P.D. Di-µ-oxido-bis [(1,4,8,11-tetraazacyclotetradecaneκ 4 N,N',N'',N''')