Paddlewheel Compounds Research Articles

Torsion Effects Beyond the δ Bond and the Role of π Metal-Ligand Interactions.

Previous studies on bimetallic paddlewheel compounds have established a direct correlation between metal-metal distance and ligand torsion angles, leading to the rule that higher torsion results in longer metal-metal bond distances. Here, the new discovery based on diarylformamidinateRu₂⁵⁺ paddlewheel compounds [Ru2Cl(DArF)4]that show an opposite behavior is reported: higher torsions lead to shorter metal-metal distances. This discovery challenges the assumption that internal rotation solely impacts the δ bond. By combining experimental and theoretical techniques, it is demostrated that this trend is associated with previously overlooked π metal-ligand interactions. These π metal-ligand interactions are a direct consequence of the paddlewheel structure and the conjugated nature of the bidentate ligands. This findings offer far-reaching insights into the influence of equatorial ligands and their π-conjugation characteristics on the electronic properties of paddlewheel complexes. That this effect is not exclusive of diruthenium compounds but also occurs in other bimetallic cores such as ditungsten or dirhodium is demonstrated, and with other ligands showing allyl type conjugation. These results provide a novel approach for fine-tuning the properties of these compounds with significant implications for materials design.

Synthesis and characterization of three new Cu(II) paddle-wheel compounds with 1,3-benzodioxole-5-carboxylic acid

Three different paddle wheel compounds have been synthesized, each one via a different synthetic pathway. The first method is the reaction of Cu(MeCO2)2·H2O with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) in a MeOH solution, yielding [Cu(µ-Pip)2(MeOH)]2 (1). The second method is the transformation of the heteroleptic core paddle-wheel compound [Cu(µ-MeCO2)(µ-Pip)(MeOH)]2 into the homoleptic core paddle-wheel [Cu(µ-Pip)2(DMSO)]2·2DMSO (2). Lastly, the third method is the substitution of the solvent molecule (DMF) present in the molecular array [Cu(µ-Pip)2(DMF)]2 by 2-benzylpyridine (2-Bzpy) ligand, resulting in [Cu(µ-Pip)2(2-Bzpy)]2·2.5MeOH·H2O (3a). All compounds are characterized via EA, PXRD, ATR-FTIR, Far-IR and UV–Vis spectroscopy. For all three compounds, the X-ray crystal structure has been determined and their extended structures are discussed. Finally, TG/DTA measurements have been recorded.

Reactivity of homoleptic and heteroleptic core paddle wheel Cu(II) compounds

The compound [Cu(µ-Pip)(µ-OAc)(MeOH)]2 (1) (Pip = Piperonylate, OAc = acetate, MeOH = methanol) has been obtained in high percentage yield. Its reactivity with pyridine/pyrazole derivative ligands (pyridine (py), 3-phenylpyridine (3-Phpy) and 4-acetylpyridine (4-Acpy)) and 3,5-dimethylpyrazole (3,5-dmpz) leads to four monomeric compounds: [Cu(Pip)2(dPy)2(H2O)] (dPy = py (2), 3-Phpy (3) and 4-Acpy (4a)) and [Cu(Pip)2(3,5-dmpz)2] (5). Furthermore, the reaction of 1 with HPip in MeOH:DMF solvent under reflux conditions yields the homoleptic core paddle-wheel compound [Cu(µ-Pip)2(DMF)]2·2DMF (6). The reaction between 6 and 2-benzylpyridine (2-Bzpy) yields the paddle-wheel core compound [Cu(Pip)2(2-Bzpy)]2 (7). All compounds have been fully characterized by analytical and spectroscopic techniques and their X-ray crystal structures have been determined. In this set of compounds, the carboxylate ligand (Pip) displays different coordination modes (monodentate (2–4), bidentate chelate (5) and bridged (1, 6 and 7)). Moreover, their extended structures are discussed: the crystal packing indicates hydrogen bond propagation, which defines 1D (2–5) or 2D (6 and 7) supramolecular networks.

Structural characterisation of diruthenium paddlewheel compounds with cytosinate and adeninate ligands

Structural characterisation of diruthenium paddlewheel compounds with cytosinate and adeninate ligands

Probing Interligand Electron Transfer in the 1MLCT S1 Excited State of trans-Mo2L2L'2 Compounds: A Comparative Study of Auxiliary Ligands and Solvents.

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states (1MLCT S1 states) of a series of quadruply bonded trans-Mo2(NN)2(O2C-X)2 paddlewheel compounds are investigated, where NN is a π-accepting phenylpropiolamidinate ligand and O2C-X (X = Me, tBu, TiPB, or CF3) is an auxiliary carboxylate ligand. The compounds show strong light absorption in the visible region due to MLCT transitions from the Mo2 center to the NN ligands. The transferred electron density was followed by femtosecond time-resolved infrared (fs-TRIR) spectroscopy with vibrational reporters such as the ethynyl groups on the NN ligands. The observed fs-TRIR spectra show that these compounds have asymmetric 1MLCT S1 excited states where the transferred electron mainly resides on a single NN ligand. The presence of interligand electron transfer (ILET) is suggested to explain the shape of the ν(C≡C) bands and the influence of auxiliary ligands and solvents on the interligand electronic coupling. The ILET in the 1MLCT S1 state is shown to be sensitive to the functional groups on the auxiliary ligands while being less responsive to changes in solvents.

Femtosecond Study of Dimolybdenum Paddlewheel Compounds with Amide/Thioamide Ligands: Symmetry, Electronic Structure, and Charge Distribution in the 1MLCT S1 State.

Four photophysically interesting dimolybdenum paddlewheel compounds are synthesized and characterized: I and II contain amide ligand (N,3-diphenyl-2-propynamide), and III and IV contain thioamide ligand (N,3-diphenyl-2-propynethioamide). I and III are trans-Mo2L2(O2C-TiPB)2-type compounds, and II and IV are Mo2L4-type compounds, where O2C-TiPB is 2,4,6-triisopropylbenzoate. I-IV display strong light absorption due to metal to ligand charge transfer (MLCT) transitions from molybdenum to the amide/thioamide ligands. Charge transfer dynamics in the MLCT excited states of I-IV have been examined using femtosecond transient absorption (fs-TA) spectroscopy and femtosecond time-resolved infrared (fs-TRIR) spectroscopy. The asymmetric amide/thioamide ligands show two forms of regioarrangements in the paddlewheel compounds. Analyses of the ν(C≡C) bands in the fs-TRIR spectra of I and II show similar electron density distribution over ligands in their 1MLCT S1 states where only two amide ligands are involved and the transferred electron is mainly localized on one of them. The fs-TRIR spectra of III and IV, however, show different charge distribution patterns where the transferred electron is fully delocalized over two thioamide ligands in III and partially delocalized in IV. Fast interligand electron transfer (ILET) was recognized as the explanation for the various charge distribution patterns, and ILET was shown to be influenced by both the ligands and the ligand arrangements.

7-Azaindol-1-yl(organo)silanes and Their PdCl2 Complexes: Pd-Capped Tetrahedral Silicon Coordination Spheres and Paddlewheels with a Pd–Si Axis

Supported by excess triethylamine, 7-azaindole (HL) and dichlorodimethylsilane (Me2SiCl2), methyltrichlorosilane (MeSiCl3), and tetrachlorosilane (SiCl4) react, respectively, with formation of the 7-azaindol-1-yl-substituted silanes Me2SiL2, MeSiL3, and SiL4. In these compounds the silicon atom adopts [4+2], [4+3], and [4+4] coordination, respectively, with the pyridine N atoms of the 7-azaindol-1-yl groups capping the tetrahedral Si coordination sphere from distances of >3 Å. Two pyridine nitrogen atoms of these silanes replace the acetonitrile ligands of [PdCl2(NCMe)2], thus forming the complexes Me2Si(μ-L)2PdCl2, MeSiL(μ-L)2PdCl2, and SiL2(μ-L)2PdCl2. In addition to capping of the silicon coordination sphere by the pyridine N atoms of the dangling 7-azaindol-1-yl groups (in MeSiL(μ-L)2PdCl2 and SiL2(μ-L)2PdCl2), these three palladium complexes exhibit capping of one tetrahedral face of the Si coordination sphere by the palladium atom (with Si···Pd separations of 3.34, 3.43, and 3.31 Å, respectively). According to computational analyses, the paddlewheel complex ClSi(μ-L)4PdCl should be energetically favored over its isomer SiL2(μ-L)2PdCl2; however, isomerization into this paddlewheel compound requires higher temperatures (150 °C) or the addition of a Lewis acid (such as GaCl3).

The usefulness of EPR spectroscopy in the study of compounds with metal–metal multiple bonds

This Perspective reviews some of the contributions that EPR spectroscopy has made for the understanding of the bonding and electronic structure of molecular species with metal-to-metal multiple bonds. The goal is to show how useful this technique can be in (a) elucidating whether unpaired electrons reside in metal-based or ligand-based molecular orbitals, (b) providing information on the metal center's total electronic spin, an aspect that offers support to its oxidation state, (c) informing about the distribution of the unpaired electrons between the metals and the organic ligand, (d) detecting molecular dynamics and phase transitions to complement X-ray studies and (e) using high-frequency, high-field EPR for studying compounds that might be EPR-silent when only commonly available spectrometers are used. A brief comparison with NMR is provided in the ESI where it is noted that for typical laboratory magnetic fields, the energy gap between resonant states in EPR is in the microwave region of the electromagnetic spectrum (GHz) while for NMR it is in the radiofrequency range (MHz). Our aim is to encourage the inorganic chemistry community and more broadly other chemists and physicists to collaborate while characterizing new paramagnetic inorganic complexes. Enough basic background is provided as ESI to allow senior-level undergraduate and graduate students to understand the simplicity as well as the power of EPR spectroscopy with a view to encourage them to use this technique in their own research activities. Finally, it should be noted that this report commemorates the fiftieth anniversary of the description in Science of the first species with a quadruple bond.

Hydrogen Bonding and Electron Transfer between Dimetal Paddlewheel Compounds Containing Pendant 2-Pyridone Functional Groups

The compounds M2(TiPB)3(HDON) (TiPB = 2,4,6-triisopropylbenzoic acid; H2DON = 2,7-dihdroxy-1,8-napthyridine; M = Mo (1a) or W (1b)) and Mo2(TiPB)2(O2CCH2Cl)(HDON) (1c) which contain a pendant 2-pyridone functional group have been prepared. These compounds are capable of forming self-complementary hydrogen bonds, resulting in the formation of "dimers of dimers" ([1a-c]2) in CH2Cl2 solutions. Electrochemical studies reveal two successive one-electron redox processes for [1a-c]2 in CH2Cl2 solutions that correspond to successive oxidations of the dimetal core, indicating stabilization of the mixed-valence state. Only small changes in the value of Kc are observed upon changing the ancillary ligand or metal, implying that proton coupled mixed valency is responsible for the stabilization. Dimethylsulfoxide (DMSO) disrupts the hydrogen bonding interactions in these compounds, and a single oxidation process is observed in DMSO which shifts to lower potential as the number of HDON ligands increases. Further substitution of carboxylate ligands with HDON leads to the formation of Mo2(TiPB)2(HDON)2 (2) and Mo2(HDON)4 (3), which adopt trans-1,1 and cis-2,2 regioisomers in the solid-state. (1)H NMR spectroscopy indicates that there are at least two regioisomers present in solution for both compounds. The lowest energy transition in the electronic absorption spectra of these compounds corresponds to a M2-δ → HDON-π* transition. The electrochemical, spectroscopic and structural results were rationalized with the aid of density functional theory (DFT) calculations.

ChemInform Abstract: Recent Developments in the Chemistry of Metal—Metal Multiply Bonded Paddlewheel Compounds

AbstractReview: 81 refs.

Tuning the Electrochemistry of Re26+ Species with Divergent Bicyclic Guanidinate Ligands and by Modification of Axial π Interactions

Four Re(2)(6+) paddlewheel compounds with equatorial bicyclic guanidinate ligands and two monodentate anions in axial positions show a large change in the metal-metal distance that depends on the bite angle of the ligands and whether there are pi interactions between the dimetal unit and the axial ligands. These processes are accompanied by significant changes in the redox behavior. The two pairs of compounds that have been synthesized are Re(2)(tbn)(4)Cl(2), 1, and Re(2)(tbn)(4)(SO(3)CF(3))(2), 2, as well as Re(2)(tbo)(4)Cl(2), 3, and Re(2)(tbo)(4)(SO(3)CF(3))(2), 4, where tbn is the anion of a bicyclic guanidinate with six- and five-membered rings (1,5,7-triazabicyclo[4.3.0]non-6-ene) and tbo is an analogous species with two five-membered rings (the anion of 1,4,6-triazabicyclo[3.3.0]oct-4-ene). For both 1 and 2 as well as for 3 and 4, the metal-metal distances are shorter for the triflate species than for the chloride analogues because of the π interactions of the Cl with the π bonds of the triply bonded Re(2)(6+) cores compounded by a small but symmetry allowed interaction between the antisymmetric combination of the filled σp orbitals of the chlorine atom and the empty σ* orbital of the metal atoms. In addition there is a significant increase in the Re-Re distance from that in the six/five tbn-membered ring to the five/five-membered tbo species. Electrochemical measurements show two redox processes for each set of compounds corresponding to the uncommon Re(2)(6+) → Re(2)(7+) and Re(2)(7+) → Re(2)(8+) processes, which are strongly affected by the bite angle of the guanidinate ligand as well as the ability of the axial ligands to interact with the π orbitals of the dirhenium unit. For 1 and 3, the first redox couples are at 0.146 and 0.487 V, respectively, while for 2 and 4 these are at 0.430 and 0.698 V, respectively.

Dicarboxylate-bridged (Mo2)n (n = 2, 3, 4) paddle-wheel complexes: potential intermediate building blocks for metal–organic frameworks

The treatment of the dimeric paddle-wheel (PW) compound [Mo(2)(NCCH(3))(10)][BF(4)](4)1 with oxalic acid (0.5 equiv.), 1,1-cyclobutanedicarboxylic acid (1 equiv.), 5-hydroxyisophthalic acid (1 equiv.) (m-bdc-OH) or 2,3,5,6-tetrafluoroterephthalic acid (0.5 or 1 equiv.) leads to the formation of macromolecular dicarboxylate-linked (Mo(2))(n) entities (n = 2, 3, 4). The structure of the compounds depends on the length and geometry of the organic linkers. In the case of oxalic acid, the dimeric compound [(CH(3)CN)(8)Mo(2)(OOC-COO)Mo(2)(NCCH(3))(8)][BF(4)](6)2 is formed selectively, whereas the use of 2,3,5,6-tetrafluoroterephthalic acid affords the square-shaped complex [(CH(3)CN)(6)Mo(2)(OOC-C(6)F(4)-COO)](4)[BF(4)](8)3. Bent linkers with a bridging angle of 109° and 120°, respectively, lead to the formation of the molecular loop [(CH(3)CN)(6)Mo(2)(OOC-C(4)H(6)-COO)](2)[BF(4)](4)4 and the bowl-shaped molecular triangle [(CH(3)CN)(6)Mo(2)(m-bdc-OH)](3)[BF(4)](6)5. All complexes are characterised by X-ray single crystal diffraction, NMR ((1)H, (11)B, (13)C and (19)F) and UV-Vis spectroscopy.

ChemInform Abstract: Substituent Effects in Dinuclear Paddlewheel Compounds: Electrochemical and Spectroscopic Investigations

Abstract This review summarizes substituent effects in dinuclear compounds supported by diarylformamidinate (form) ligands, where aryl is phenyl substituted with various polar groups (X). These dinuclear compounds, M2(form)4(Lax)m with M as Mo, Ru, Rh, or Ni, Lax as either neutral or anionic axial ligand, and m=0–2, may undergo up to three (quasi)reversible one-electron, metal-centered redox processes. Linear correlations have been established between the electrode potentials (E1/2, Epc or Epa) and the substituent constants (σ) according to the following Hammett equation: ΔE=E(X)−E(H)=ρ(Σ σ), with the reaction constant ρ ranging from +60 to +100 mV. The existence of such relationships indicates that the energy levels of the frontier orbitals of dinuclear species are controlled precisely by the substituent within each series, and generally decrease with an increase in the electron withdrawing ability of the substituent. However, nearly identical UV–vis absorption spectra were observed within each homologous series, and one can infer a minimal substituent perturbation on the distribution of upper valence molecular orbitals. Axial ligation of organic π acids such as CO and phenylacetylide in both the diruthenium and dirhodium series also provides insight to the activation of these substrates by the dinuclear core, and the linear free energy relationship therein. A brief overview of other investigations of substituent effects in dinuclear compounds is provided also.

Large Changes in Electronic Structures of Ru26+ Species Caused by the Variations of the Bite Angle of Guanidinate Ligands: Tuning Magnetic Behavior

Syntheses and characterization of two Ru(2)(6+) paddlewheel compounds having very different magnetic behavior are reported. The compounds Ru(2)(tbn)(4)Cl(2), 1, and Ru(2)(tbo)(4)Cl(2), 2 (where tbn = the anion of 1,5,7-triazabicyclo[4.3.0]non-6-ene and tbo = the anion of 1,4,6-triazabicyclo[3.3.0]oct-4-ene), have four equatorial bicyclic guanidinate ligands and two chloride ions in axial positions. They show large disparity in Ru-Ru distances of about 0.11 A (2.389(3) and 2.499(3) A at 30 K for 1 and 2, respectively) that is attributed to the divergence in the bite angle of the ligand. Variable temperature structural data show no significant changes in the Ru-Ru distances between 30 and 213 K suggesting that the electronic structure remains unchanged in this temperature range for both compounds. Magnetic studies of 1 indicate there are two unpaired electrons at room temperature but the compound behaves as essentially diamagnetic at approximately 2 K. Compound 2 is non-magnetic across all temperatures in the range of 2 to 300 K. Density functional theory calculations suggest a pi(4)pi*(4)delta(2) electronic configuration for 2, while the magnetic behavior and structural data for 1 are consistent with a sigma(2)pi(4)delta(2)pi*(2) electronic configuration. This shows the importance of the ligand bite angle in determining the electronic configuration of the diruthenium unit and a way to tune magnetic behavior.

First microwave synthesis of multiple metal-metal bond paddlewheel compounds

A green and efficient microwave assisted synthesis of elusive tetrakis(diaryltriazenido)diruthenium(II) complexes was carried out under microwave irradiation. It is a simple, clean, and fast method that proceeds with good yield, in contrast with the poor ones reported in previous syntheses.

Proof by EPR Spectroscopy that the Unpaired Electron in an Os27+ Species Is in a δ* Metal-based Molecular Orbital

Variable temperature structural and EPR studies are reported on the paddlewheel compound [Os(2)(hpp)(4)Cl(2)]PF(6), 1, (hpp = the anion of the bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) that contains a rare M(2)(7+) species, with the goal of determining whether the unpaired electron resides in a metal- or ligand-based molecular orbital. Crystallographic studies show that the Os-Os distance in 1 remains essentially unchanged from 213 to 30 K, which is consistent with no changes in electronic structure in this range of temperature. It is noteworthy that the metal-metal distance in 1 is about 0.05 A shorter than that in the precursor Os(2)(hpp)(4)Cl(2), which is consistent with the loss of an electron in a delta* orbital. EPR spectra of 1 were measured in dilute frozen solution, powder, and single crystals. The spectra were observable only below about 50 K, with an exceptionally large line width, approximately 3,750 gauss, for a powdered sample, due to dipolar interactions and to short relaxation times. There is a very small average g value of approximately 0.750 and a cylindrical symmetry about the Os-Os bond. These data are consistent with the unpaired electron orbital having a large L value, such as that of a delta* orbital. The combination of X-ray structural data, the short relaxation time, and the magnetic data provide strong evidence that the unpaired electron in this nine-electron Os(2)(7+) species is localized in a metal-based orbital with this electron residing predominantly in a delta* orbital rather than in a pi* orbital and, thus, having an electronic configuration of sigma(2)pi(4)delta(2)delta*.

2-Mercapto-1- t-butylimidazolyl as a bridging ligand: Synthesis and structural characterization of nickel and palladium paddlewheel complexes

Nickel and palladium paddlewheel complexes that feature 2-mercapto-1- t-butylimidazolyl ( mim Bu t ) bridging ligands, namely Ni 2[ mim Bu t ] 4 and Pd 2[ mim Bu t ] 4, have been synthesized and structurally characterized by X-ray diffraction. Since the mim Bu t ligand bridges in an asymmetric manner via a sulfur and nitrogen donor, paddlewheel compounds of the type M 2[ mim Bu t ] 4 may exist as isomers that are distinguished by the relative orientations of the ligands. In this regard, the (4,0)-Ni 2[ mim Bu t ] 4 and trans-(2,2)-Ni 2[ mim Bu t ] 4 isomers have been isolated for the nickel system, while the (4,0)-Pd 2[ mim Bu t ] 4 and (3,1)-Pd 2[ mim Bu t ] 4 isomers have been isolated for the palladium system.

Activation of isocyanate ligands in [formula omitted] complexes

The reaction of [Ru 2(O 2CMe)(DPhF) 3(H 2O)]BF 4 · 0.5CH 2Cl 2 (DphF N, N′-diphenylformidinate) with sodium cyanate leads to the substitution of the H 2O ligand giving Ru 2(NCO)(O 2CMe)(DPhF) 3 ( 1). In contrast, in the similar reaction of Ru 2Cl 2(DPhF) 3 with NaOCN one of the cyanate groups undergoes the addition of a MeOH molecule leading to the carbamate complex Ru 2(NCO)(NH(O)COMe)(DPhF) 3 ( 2). The spectroscopic properties of 1 and 2 are studied. Both complexes are paramagnetic showing the presence of three unpaired electrons with an important zero-field splitting and a small intermolecular antiferromagnetic interaction. The crystal structures of 1 · 3CHCl 3 and 2 · C 7H 8 · 0.5MeOH are also reported. Compound 2 represents the first example of a ruthenium paddlewheel compound with a carbamate ligand.

Three new polynuclear tetracarboxylato-bridged copper(II) complexes: Syntheses, X-ray structure and magnetic properties

The synthesis, crystal structure and magnetic measurements of three new polynuclear tetracarboxylato-bridged copper(II) complexes, i.e. {[Cu 4(phen) 2(μ-O 2CC 2H 5) 8] · (H 2O)} n ( 1), [Cu 2(μ-O 2CC 6H 4OH) 4(C 7H 7NO) 2] · 6H 2O ( 2) and [Cu 2(μ-O 2CCH 3) 4(C 7H 7NO) 2] ( 3) (phen = 1,10-phenanthroline, O 2CC 6H 4OH = 3-hydroxy benzoate, C 7H 7NO = 4-acetylpyridine) are reported. All compounds consist of dinuclear units, in which two Cu(II) ions are bridged by four syn, syn-η 1:η 1:μ carboxylates, showing a paddle-wheel cage type with a square-pyramidal geometry, arranged in different ways. The structure of compound 1 consists of an one-dimensional structure generated by an alternating classical dinuclear paddle-wheel unit and an unusual dinuclear Cu 2(μ-OCOC 2H 5) 2(μ-O 2CC 2H 5) 2(phen) 2unit, which are connected to each other via a syn, anti-triatomic propionato bridge in an axial-equatorial configuration. The adjacent chains are connected to generate a 2D structure through the face-to-face π–π interaction between phen rings. Structures of compounds 2 and 3 both consist of a symmetric dinuclear Cu(II) carboxylate paddle-wheel core and pyridyl nitrogen atoms of 4-acetylpyridine ligand at the apical position, and just differ in the substituents of the equatorial ligands. The magnetic properties have been measured and correlated with the molecular structures. It is found that in the two classical paddle-wheel compounds the Cu(II) ions are strongly antiferromagnetically coupled with J = −278.5 and −287.0 cm −1 for complexes 2 and 3, respectively. In compound 1 the magnetic susceptibility could be fitted with two different, independent Cu(II) units, one strongly coupled and one weakly coupled; the paddle-wheel dinuclear unit has the strongest antiferromagetic coupling with a value for J of −299.5 cm −1, whereas the Cu(II) ions in the propionato-bridged dinuclear unit of 1 display a very weak antiferromagnetic coupling with a value for J = −0.75 cm −1, due to the orthogonality of the magnetic orbitals. Also the exchange within the chain is therefore very weak. The magneto-structural correlations for complexes 1, 2, and 3 are discussed on the basis of the structural parameters and magnetic data for the complexes.

A Tetragonal and an Uncommon Trigonal Dicobalt Paddlewheel Compound

Two dicobalt compounds containing Co–Co bonds with DAniF ligands (DAniF = N,N′-di-p-anisylformamidinate) were synthesized and characterized by X-ray crystallography. One has a typical tetragonal paddlewheel structure, Co2(DAniF)4 (1), while the other one has a rare trigonal paddlewheel structure with three formamidinate ligands spanning a low oxidation state in the Co 2 3+ unit in Co2(DAniF)3 (2). The singly bonded Co–Co distance in the Co 2 4+ unit in 1 is 2.3580(16) A while the Co–Co bond distance in 2 is 2.3773(5) A. The average torsion angles are 10.46° and 2.34° for 1 and 2, respectively. Compound 1 is diamagnetic but 2 is paramagnetic as shown by the 1H NMR spectra.