b S Supporting Information 2,5-D ihydroxybenzoquinone (I, hereafter H 2 dhbq) and chloranilic acid (II, hereafter H 2 can) upon deprotonation provide dianionic ligands capable of chelating a single metal center to give mononuclear complexes.They are capable also of bridging two metal centers to yield binuclear and oligomeric complexes as well as 1D, 2D, and 3D polymers. A feature of major interest in these systems is their ability to exist, after deprotonation, not only as the À2 anion but also as the relatively stable À1 or À3 radical anions, as well as the À4 anion. Electrochemical studies of dhbq-bridged and canbridged binuclear complexes reveal that radical oxidation states of the organic bridges are easily achieved. 1 Some of the longer term objectives of our group are to discover dhbq-based or canbased coordination polymers in which (a) some or all of the bridging ligands are in a radical state, or (b) both the metal centers and the bridging ligands carry unpaired electrons, or (c) both metal and ligand components are amenable to facile electron transfer. These various circumstances may lead to interesting and possibly useful electronic/magnetic properties.On the basis of the many structural studies of dhbq 2À -based and can 2À -based coordination polymers in the literature, we present here a very brief overview of the major structural types known at present. A number of 1D polymers (generally M 2+ / can 2À or M 2+ /dhbq 2À ) are known in which the octahedral metal components of the chain carry two monodentate ligands such as H 2 O. If these two ligands are trans, a linear polymer results in which the dhbq 2À or can 2À components are essentially coplanar, 2 whereas if the two are cis, a zigzag conformation is adopted. 2c,3 Related zigzag polymers are formed when a single bidentate ligand occupies two cis positions. 4 In some cases, neutral bridging ligands (other than can 2À or dhbq 2À ) link M/can or M/dhbq ABSTRACT: Crystalline compounds of general composition (NBu 4 ) 2 [M II 2 (dhbq) 3 ] (where M = Mn, Fe, Co, Ni, Zn, and Cd and dhbq 2À is the dianion of 2,5-dihydroxybenzoquinone) are obtained by reaction of the divalent metal acetate (or the sulfate in the case of Fe) with 2,5-diaminobenzoquinone and an excess of NBu 4 Br in aqueous solution at 115°C in sealed tubes. The dhbq 2À ligand is generated in situ by hydrolysis of the 2,5-diaminobenzoquinone. We have been unable to obtain these compounds in a crystalline form suitable for single crystal X-ray diffraction studies directly from H 2 dhbq itself. A structural feature common to this series is the presence of two interpenetrating [M II 2 (dhbq) 3 ] 2À coordination networks, each with the chiral (10,3)-a topology, with the two independent nets being of opposite hand-unprecedented circumstances for dhbq-based coordination polymers. Crystals of the same zinc compound as that obtained above from 2,5-diaminobenzoquinone can alternatively be obtained by in situ aerial oxidation of 1,2,4,5-tetrahydroxybenzene in the presence of Zn(OAc) 2 and NBu 4 Br in aq...

In the presence of the Et 4 N + cation the chloranilate dianion (can 2− ) associates with a range of divalent cations, M 2+ , to yield an isomorphous series of crystalline compounds of composition (Et 4 N) 2 [M 2 (can) 3 ] (M = Mg, Mn, Fe, Co, Ni, Cu, and Zn). The fluoranilate dianion (fan 2− ) likewise affords the closely related (Et 4 N) 2 [Zn 2 (fan) 3 ]. The structures of (Et 4 N) 2 [Zn 2 (can) 3 ], (Et 4 N) 2 [Fe 2 (can) 3 ], and (Et 4 N) 2 [Zn 2 (fan) 3 ] were determined by single crystal X-ray diffraction. Powder X-ray diffraction indicates that all the members of the can 2− series are isomorphous. The structure of (Et 4 N) 2 [Zn 2 (fan) 3 ] is very closely related to the structures of the can 2− compounds. The [M 2 (can) 3 2−

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A pair of coordination polymers of composition (NBu)[M(fan)] (fan = fluoranilate; M = Fe and Zn) were synthesized and structurally characterized. In each case the compound consists of a pair of interpenetrating three-dimensional, (10,3)-a networks in which metal centers are linked by chelating/bridging fluoranilate ligands. Tetrabutylammonium cations are located in the spaces between the two networks. Despite the structural similarity, significant differences exist between (NBu)[Fe(fan)] and (NBu)[Zn(fan)] with respect to the oxidation states of the metal centers and ligands. For (NBu)[Fe(fan)] the structure determination as well as Mössbauer spectroscopy indicate the oxidation state for the Fe is close to +3, which contrasts with the +2 state for the Zn analogue. The differences between the two compounds extends to the ligands, with the Zn network involving only fluoranilate dianions, whereas the average oxidation state for the fluoranilate in the Fe network lies somewhere between -2 and -3. Magnetic studies on the Fe compound indicate short-range ordering. Electrochemical and spectro-electrochemical investigations indicate that the fluoranilate ligand is redox-active in both complexes; a reduced form of (NBu)[Fe(fan)] was generated by chemical reduction. Conductivity measurements indicate that (NBu)[Fe(fan)] is a semiconductor, which is attributed to the mixed valency of the fluoranilate ligands.

Aqueous reaction mixtures containing citric acid, guanidinium carbonate, and a range of metal cations (Mg2+, Mn2+, Fe2+, Co2+, Ni2+, and Zn2+) at room temperature give crystalline products of composition [C(NH2)3]8[(M(II))4(cit)4].8H2O (cit = citrate). In all cases, the crystals are suitable for single-crystal X-ray diffraction studies, which reveal that the compounds are isostructural (space group P4(2)/n; a approximately 16.2 A, and c approximately 11.5 A). As was intended, cubane-like [M4(cit)4]8- complex anions are present. The individual citrate units are chiral, but each cubane unit contains two of one hand and two of the other, related around an S4 axis. The cubane units are involved in no less than 40 H-bonding interactions with guanidinium cations and lattice water molecules. Detailed susceptibility and magnetization studies show that the intracluster magnetic coupling within the Mn(II), Fe(II), Co(II), and Ni(II) cubanes is very weak in all cases with J values of -0.82, -0.43, and -0.09 cm(-1) for the Mn, Fe, and Co species, respectively. A two-J model gave the best agreement with the susceptibility and high-field magnetization data for the Ni(II) case, over the whole temperature range studied, and the sign of the parameters, J12 = -0.3 cm(-1) and J13 = +2.97 cm(-1), correlated with the two Ni-(mu3-O)-Ni angles observed in the cluster structure. All members of the 3d-block [M4(cit)4]8- family have spin ground states, ST, of zero, with the higher ST levels just a few reciprocal centimeters away in energy.