Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103004360/sq1009sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270103004360/sq1009Isup2.hkl |
CCDC reference: 211733
Sodium 2-ethoxy-1,1,3,3-tetracyanopropenide (150 mg, 0.72 mmol), prepared according to the literature procedure of Middleton et al. (1957), was dissolved in water (10 ml) and combined with an ethanolic solution (10 ml) of pyrazine (Aldrich, 58 mg, 0.72 mmol). This solution was layered on top of an aqueous solution (10 ml) of manganese(II) nitrate hydrate (Aldrich, 64 mg, 0.36 mmol). After one month, clear colorless blocky crystals of (I) were collected from the concentrated solution by filtration. Decomposition begins near 453 K as the clear crystals become opaque, possibly as a result of water loss.
Ethoxy H atoms were placed geometrically and refined with a riding model, and with Uiso constrained to be 1.2 or 1.5Ueq of the methylene and methyl C atoms, respectively. Water H-atom positions were refined under distance and angle restraints, with Uiso constrained to be 1.5Ueq of atom O2.
Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
[Mn(C9H5N4O)2(H2O)2] | Z = 1 |
Mr = 461.31 | F(000) = 235 |
Triclinic, P1 | Dx = 1.363 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 8.3288 (4) Å | Cell parameters from 1000 reflections |
b = 8.5220 (4) Å | θ = 2.3–32.0° |
c = 9.3793 (5) Å | µ = 0.63 mm−1 |
α = 81.387 (2)° | T = 298 K |
β = 69.135 (2)° | Block, colorless |
γ = 64.589 (2)° | 0.56 × 0.30 × 0.17 mm |
V = 561.88 (5) Å3 |
Siemens SMART CCD area-detector diffractometer | 3763 independent reflections |
Radiation source: fine-focus sealed tube | 3321 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.022 |
area detector ω scans | θmax = 32.0°, θmin = 2.3° |
Absorption correction: integration (SHELXTL; Sheldrick, 2001) | h = −12→12 |
Tmin = 0.802, Tmax = 0.898 | k = −12→12 |
7918 measured reflections | l = −13→13 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.032 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.091 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.02 | w = 1/[σ2(Fo2) + (0.0485P)2 + 0.0745P] where P = (Fo2 + 2Fc2)/3 |
3763 reflections | (Δ/σ)max = 0.014 |
148 parameters | Δρmax = 0.30 e Å−3 |
3 restraints | Δρmin = −0.29 e Å−3 |
[Mn(C9H5N4O)2(H2O)2] | γ = 64.589 (2)° |
Mr = 461.31 | V = 561.88 (5) Å3 |
Triclinic, P1 | Z = 1 |
a = 8.3288 (4) Å | Mo Kα radiation |
b = 8.5220 (4) Å | µ = 0.63 mm−1 |
c = 9.3793 (5) Å | T = 298 K |
α = 81.387 (2)° | 0.56 × 0.30 × 0.17 mm |
β = 69.135 (2)° |
Siemens SMART CCD area-detector diffractometer | 3763 independent reflections |
Absorption correction: integration (SHELXTL; Sheldrick, 2001) | 3321 reflections with I > 2σ(I) |
Tmin = 0.802, Tmax = 0.898 | Rint = 0.022 |
7918 measured reflections |
R[F2 > 2σ(F2)] = 0.032 | 3 restraints |
wR(F2) = 0.091 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.02 | Δρmax = 0.30 e Å−3 |
3763 reflections | Δρmin = −0.29 e Å−3 |
148 parameters |
Experimental. The data collection nominally covered over a hemisphere of reciprocal space, by a combination of three sets of exposures; each set had a different ϕ angle for the crystal and each exposure covered 0.3° in ω. The crystal-to-detector distance was 4.02 cm. Coverage of the unique set was over 95% complete to at least 30.8° in θ, over 99% complete to at least 30.5° in θ. Crystal decay was monitored by repeating the initial 50 frames at the end of data collection and analyzing the duplicate reflections. Decay was found to be less than 1%, and no decay correction was therefore applied. |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
Mn1 | 0.5000 | 0.0000 | 0.0000 | 0.03213 (8) | |
O1 | −0.43193 (12) | 0.39205 (13) | 0.33564 (11) | 0.0485 (2) | |
N1 | −0.2798 (2) | 0.0179 (2) | 0.51965 (15) | 0.0693 (4) | |
N2 | 0.20933 (14) | 0.03498 (16) | 0.13662 (13) | 0.0479 (3) | |
N3 | 0.05351 (17) | 0.22325 (18) | −0.14891 (14) | 0.0563 (3) | |
N4 | −0.38877 (17) | 0.71315 (14) | 0.02737 (15) | 0.0524 (3) | |
C1 | −0.21734 (17) | 0.08245 (18) | 0.41148 (14) | 0.0447 (3) | |
C2 | 0.05068 (15) | 0.09102 (15) | 0.19925 (13) | 0.0367 (2) | |
C3 | −0.06721 (16) | 0.29736 (15) | −0.04356 (14) | 0.0389 (2) | |
C4 | −0.31460 (17) | 0.56999 (15) | 0.05451 (15) | 0.0402 (2) | |
C5 | −0.14447 (14) | 0.16424 (15) | 0.27649 (12) | 0.0356 (2) | |
C6 | −0.26621 (14) | 0.31830 (14) | 0.22797 (13) | 0.0342 (2) | |
C7 | −0.21947 (15) | 0.39306 (14) | 0.08284 (13) | 0.0359 (2) | |
C8 | −0.60236 (18) | 0.4995 (2) | 0.3007 (2) | 0.0629 (4) | |
H8A | −0.5943 | 0.4650 | 0.2036 | 0.075* | |
H8B | −0.6205 | 0.6204 | 0.2939 | 0.075* | |
C9 | −0.7618 (2) | 0.4773 (3) | 0.4244 (3) | 0.0895 (7) | |
H9A | −0.8768 | 0.5474 | 0.4033 | 0.134* | |
H9B | −0.7691 | 0.5127 | 0.5198 | 0.134* | |
H9C | −0.7426 | 0.3575 | 0.4301 | 0.134* | |
O2 | 0.44706 (13) | −0.01725 (14) | −0.20677 (10) | 0.0471 (2) | |
H21 | 0.343 (2) | 0.048 (2) | −0.212 (2) | 0.071* | |
H22 | 0.521 (2) | −0.004 (2) | −0.2875 (18) | 0.071* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Mn1 | 0.02289 (11) | 0.02929 (12) | 0.03303 (12) | −0.00629 (8) | −0.00370 (8) | 0.00433 (8) |
O1 | 0.0269 (4) | 0.0551 (5) | 0.0424 (5) | −0.0024 (4) | −0.0020 (3) | −0.0088 (4) |
N1 | 0.0577 (8) | 0.0906 (10) | 0.0434 (7) | −0.0326 (8) | −0.0029 (6) | 0.0191 (6) |
N2 | 0.0275 (4) | 0.0568 (6) | 0.0438 (6) | −0.0116 (4) | −0.0065 (4) | 0.0140 (5) |
N3 | 0.0455 (6) | 0.0587 (7) | 0.0424 (6) | −0.0071 (5) | −0.0063 (5) | −0.0020 (5) |
N4 | 0.0489 (6) | 0.0341 (5) | 0.0607 (7) | −0.0092 (5) | −0.0140 (5) | 0.0049 (5) |
C1 | 0.0330 (5) | 0.0551 (7) | 0.0341 (6) | −0.0143 (5) | −0.0043 (4) | 0.0056 (5) |
C2 | 0.0284 (5) | 0.0400 (5) | 0.0337 (5) | −0.0117 (4) | −0.0075 (4) | 0.0086 (4) |
C3 | 0.0338 (5) | 0.0355 (5) | 0.0389 (6) | −0.0089 (4) | −0.0109 (4) | 0.0055 (4) |
C4 | 0.0351 (5) | 0.0334 (5) | 0.0455 (6) | −0.0102 (4) | −0.0108 (5) | 0.0007 (4) |
C5 | 0.0252 (4) | 0.0388 (5) | 0.0324 (5) | −0.0101 (4) | −0.0030 (4) | 0.0039 (4) |
C6 | 0.0248 (4) | 0.0344 (5) | 0.0361 (5) | −0.0082 (4) | −0.0048 (4) | −0.0037 (4) |
C7 | 0.0302 (5) | 0.0290 (5) | 0.0396 (5) | −0.0068 (4) | −0.0084 (4) | 0.0012 (4) |
C8 | 0.0264 (5) | 0.0716 (10) | 0.0674 (10) | −0.0058 (6) | −0.0069 (6) | 0.0002 (8) |
C9 | 0.0359 (8) | 0.1136 (18) | 0.0956 (15) | −0.0259 (10) | 0.0007 (9) | −0.0035 (13) |
O2 | 0.0347 (4) | 0.0611 (6) | 0.0339 (4) | −0.0147 (4) | −0.0049 (3) | 0.0012 (4) |
Mn1—O2 | 2.1743 (10) | C1—C5 | 1.4172 (16) |
Mn1—N2 | 2.2084 (10) | C2—C5 | 1.4079 (14) |
Mn1—N4i | 2.2221 (11) | C3—C7 | 1.4177 (16) |
O1—C6 | 1.3314 (12) | C4—C7 | 1.4059 (15) |
O1—C8 | 1.4447 (17) | C5—C6 | 1.4022 (15) |
N1—C1 | 1.1424 (17) | C6—C7 | 1.4093 (16) |
N2—C2 | 1.1439 (14) | C8—C9 | 1.482 (2) |
N3—C3 | 1.1491 (16) | O2—H21 | 0.824 (14) |
N4—C4 | 1.1432 (16) | O2—H22 | 0.816 (14) |
O2ii—Mn1—O2 | 180.00 (5) | N1—C1—C5 | 178.48 (15) |
O2ii—Mn1—N2 | 89.89 (4) | N2—C2—C5 | 178.50 (14) |
O2—Mn1—N2 | 90.11 (4) | N3—C3—C7 | 177.92 (13) |
O2ii—Mn1—N2ii | 90.11 (4) | N4—C4—C7 | 178.11 (15) |
O2—Mn1—N2ii | 89.89 (4) | C6—C5—C2 | 122.20 (10) |
N2—Mn1—N2ii | 180.00 (3) | C6—C5—C1 | 119.45 (10) |
O2ii—Mn1—N4i | 88.59 (5) | C2—C5—C1 | 118.29 (10) |
O2—Mn1—N4i | 91.41 (5) | O1—C6—C5 | 112.98 (10) |
N2—Mn1—N4i | 92.81 (5) | O1—C6—C7 | 122.44 (10) |
N2ii—Mn1—N4i | 87.19 (5) | C5—C6—C7 | 124.55 (10) |
O2ii—Mn1—N4iii | 91.41 (5) | C4—C7—C6 | 122.47 (10) |
O2—Mn1—N4iii | 88.59 (5) | C4—C7—C3 | 115.00 (10) |
N2—Mn1—N4iii | 87.19 (5) | C6—C7—C3 | 122.46 (10) |
N2ii—Mn1—N4iii | 92.81 (5) | O1—C8—C9 | 107.99 (15) |
N4i—Mn1—N4iii | 180.00 (7) | Mn1—O2—H21 | 116.5 (14) |
C6—O1—C8 | 122.62 (11) | Mn1—O2—H22 | 116.8 (14) |
C2—N2—Mn1 | 164.73 (11) | H21—O2—H22 | 104.6 (18) |
C4—N4—Mn1iv | 168.27 (12) | ||
O2ii—Mn1—N2—C2 | 93.5 (4) | C2—C5—C6—C7 | 15.74 (19) |
O2—Mn1—N2—C2 | −86.5 (4) | C1—C5—C6—C7 | −167.15 (12) |
N4i—Mn1—N2—C2 | −178.0 (4) | O1—C6—C7—C4 | 19.80 (18) |
N4iii—Mn1—N2—C2 | 2.0 (4) | C5—C6—C7—C4 | −158.06 (12) |
C8—O1—C6—C5 | −152.09 (13) | O1—C6—C7—C3 | −163.34 (12) |
C8—O1—C6—C7 | 29.82 (19) | C5—C6—C7—C3 | 18.80 (19) |
C2—C5—C6—O1 | −162.30 (11) | C6—O1—C8—C9 | 148.17 (16) |
C1—C5—C6—O1 | 14.81 (17) |
Symmetry codes: (i) x+1, y−1, z; (ii) −x+1, −y, −z; (iii) −x, −y+1, −z; (iv) x−1, y+1, z. |
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H21···N3 | 0.82 (1) | 2.13 (2) | 2.9223 (16) | 161 (2) |
O2—H22···N1v | 0.82 (1) | 2.02 (1) | 2.8366 (15) | 176 (2) |
Symmetry code: (v) x+1, y, z−1. |
Experimental details
Crystal data | |
Chemical formula | [Mn(C9H5N4O)2(H2O)2] |
Mr | 461.31 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 298 |
a, b, c (Å) | 8.3288 (4), 8.5220 (4), 9.3793 (5) |
α, β, γ (°) | 81.387 (2), 69.135 (2), 64.589 (2) |
V (Å3) | 561.88 (5) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 0.63 |
Crystal size (mm) | 0.56 × 0.30 × 0.17 |
Data collection | |
Diffractometer | Siemens SMART CCD area-detector diffractometer |
Absorption correction | Integration (SHELXTL; Sheldrick, 2001) |
Tmin, Tmax | 0.802, 0.898 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7918, 3763, 3321 |
Rint | 0.022 |
(sin θ/λ)max (Å−1) | 0.746 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.032, 0.091, 1.02 |
No. of reflections | 3763 |
No. of parameters | 148 |
No. of restraints | 3 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.30, −0.29 |
Computer programs: SMART (Siemens, 1995), SAINT (Bruker, 2001), SAINT, SHELXTL (Sheldrick, 2001), SHELXTL.
Mn1—O2 | 2.1743 (10) | N4—C4 | 1.1432 (16) |
Mn1—N2 | 2.2084 (10) | C1—C5 | 1.4172 (16) |
Mn1—N4i | 2.2221 (11) | C2—C5 | 1.4079 (14) |
O1—C6 | 1.3314 (12) | C3—C7 | 1.4177 (16) |
O1—C8 | 1.4447 (17) | C4—C7 | 1.4059 (15) |
N1—C1 | 1.1424 (17) | C5—C6 | 1.4022 (15) |
N2—C2 | 1.1439 (14) | C6—C7 | 1.4093 (16) |
N3—C3 | 1.1491 (16) | C8—C9 | 1.482 (2) |
O2ii—Mn1—N2 | 89.89 (4) | C6—C5—C2 | 122.20 (10) |
O2ii—Mn1—N4i | 88.59 (5) | C6—C5—C1 | 119.45 (10) |
N2ii—Mn1—N4i | 87.19 (5) | C2—C5—C1 | 118.29 (10) |
C6—O1—C8 | 122.62 (11) | O1—C6—C5 | 112.98 (10) |
C2—N2—Mn1 | 164.73 (11) | O1—C6—C7 | 122.44 (10) |
C4—N4—Mn1iii | 168.27 (12) | C5—C6—C7 | 124.55 (10) |
N1—C1—C5 | 178.48 (15) | C4—C7—C6 | 122.47 (10) |
N2—C2—C5 | 178.50 (14) | C4—C7—C3 | 115.00 (10) |
N3—C3—C7 | 177.92 (13) | C6—C7—C3 | 122.46 (10) |
N4—C4—C7 | 178.11 (15) | O1—C8—C9 | 107.99 (15) |
C8—O1—C6—C5 | −152.09 (13) | O1—C6—C7—C4 | 19.80 (18) |
C8—O1—C6—C7 | 29.82 (19) | C5—C6—C7—C4 | −158.06 (12) |
C2—C5—C6—O1 | −162.30 (11) | O1—C6—C7—C3 | −163.34 (12) |
C1—C5—C6—O1 | 14.81 (17) | C5—C6—C7—C3 | 18.80 (19) |
C2—C5—C6—C7 | 15.74 (19) | C6—O1—C8—C9 | 148.17 (16) |
C1—C5—C6—C7 | −167.15 (12) |
Symmetry codes: (i) x+1, y−1, z; (ii) −x+1, −y, −z; (iii) x−1, y+1, z. |
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H21···N3 | 0.824 (14) | 2.130 (15) | 2.9223 (16) | 161.3 (19) |
O2—H22···N1iv | 0.816 (14) | 2.022 (14) | 2.8366 (15) | 175.6 (19) |
Symmetry code: (iv) x+1, y, z−1. |
Coordination polymers formed by linking various transition metal centers with pseudohalides have been intensely studied over the past decade in an attempt to correlate their structural and magnetic properties. The dicyanamide (dca) anion, N(CN)2−, which has a propensity to act as a bidentate ligand, mediates ferromagnetic coupling in Ni(dca)2 at a temperature as high as 21 K (Kurmoo & Kepert, 1998). More recently, various cyanocarbons have been investigated as potential superexchange ligands. We have found that the carbamoyldicyanomethanide (cdm) anion, (CN)2CC(O)NH2−, favors the formation of the mononuclear [M(cdm)2(H2O)4]·2H2O complex (M is Mn, Co, Ni or Cu; Schlueter et al., 2003). In an attempt to provide additional nitrile binding sites, and thus enhance the probability of forming polymeric structures, we have turned our attention to the crystallization of various polynitrile transition metal complexes.
2-Alkoxytetracyanoallyl anions have recently been used as components of charge-transfer salts because of their synthetic versitility, large polarizabilities and potential for intermolecular contacts with the donor molecules. The 2-ethoxy-1,1,3,3-tetracyanopropenide (EtO-TCA) salts of tetrathiotetracene (TTT), (TTT)(EtO-TCA)(thf)0.25 (thf is tetrahydrofuran) and (TTT)(EtO-TCA)2, exhibit semiconducting behavior (Sekizaki, Tada et al., 2001). The salt with bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), α-(BEDT-TTF)2(EtO-TCA)(thf)0.5, is also a semiconductor (Sekizaki Yamochi & Saito, 2001). The bis(ethylenedioxo)tetrathiafulvalene (BEDO-TTF) salt, (BEDO-TTF)2(EtO-TCA), exhibits successive metal-semiconductor and semiconductor-metal transitions near 150 K and 40 K, respectively (Sekizaki et al., 2002). Until this work, EtO-TCA has not been studied as the bridging component of transition-metal-based coordination polymers. In this paper, we report that EtO-TCA is capable of bridging transition metal ions to form the title Mn(EtO-TCA)2(H2O)2 complex, (I). \sch
Similar to the data reported for other structures of the EtO-TCA anion (Sekizaki, Tada et al., 2001), the C—C bond lengths of the tetracyanopropenide moiety of (I), 1.4022 (15)–1.4177 (16) Å, are intermediate between typical single and double bonds, indicating a delocalized electronic structure. The Cmethanide—Cnitrile bonds are about 0.01 Å longer for the non-coordinated nitrile groups than for the coordinated ones.
The EtO-TCA anions in (I) bridge two Mn atoms through one of the nitrile N atoms of each of its two dicyanomethanide units (Fig. 1). With respect to the ethoxy group, one coordinating nitrile is cis while the second is trans. The five-atom bridging moiety is markedly distorted from planarity. Intramolecular EtO-TCA planes are defined as by Sekizaki (Sekizaki, Tada et al., 2001). The propyl C atoms (C5, C6 and C7) define plane 1 (P1). The two dicyanomethanide planes, P2 (N1, C1, C5, C2 and N2) and P3 (N3, C3, C7, C4 and N4) are canted 32.08 (8)° with respect to each other. The r.m.s. deviation of P2 is 0.006 Å, with the greatest deviation, 0.010 (1) Å, occurring for atom C2. Similarly, for P3, the r.m.s. deviation is 0.004 Å, with the greatest deviation, 0.007 (1) Å, occurring for atom C3. The dihedral angles of P1 with P2 and P3 are 14.83 (15) and 20.64 (15)°, respectively. The C1—C5···C7—C4 torsion angle is 55.7 (3)°. Atoms C6, O1 and C8 define plane 4 (P4), which has a dihedral angle of 28.7 (1)° with P1.
Crystal-packing forces are responsible for distorting the EtO-TCA− anion from the planar structure predicted by molecular orbital calculations. RHF/6–31 G* calculations have been used to predict the P1—P2, P2—P3, P1—P3, and P1—P4 dihedral angles as a function of the C1—C5···C7—C4 torsion angle (Sekizaki, Tada et al., 2001). These calculations are in line with the molecular structure of EtO-TCA− as observed in (I), except for the P1—P4 dihedral angle, which is significantly less than predicted. A similar discrepancy was also observed in (TTT)(BuO-TCA) and attributed to crystal-packing forces by Sekizaki, Tada et al. (2001).
The centrosymmetric coordination sphere about the Mn atom in (I) consists of the O atoms of two water molecules and the nitrile N atoms (N2 and N4) of four EtO-TCA− anions in an essentially octahedral environment. A distortion of 2.81 (5)° is seen in the N2—Mn—N4 angle (Table 1). The Mn—N and Mn—O bond lengths (Table 1) are typical for nitrile coordination to Mn (see e.g. Dalai et al., 2002; Schlueter et al., 2003).
The EtO-TCA− anions act as bidentate ligands in (I), forming dibridged chains along the ab direction (Fig 2). The coordinating nitrile N atoms are on opposing dicyanomethanide groups of EtO-TCA−, resulting in a seven-atom bridge and an intrachain Mn···Mn separation of 9.0044 (4) Å. Slightly shorter interchain Mn···Mn separations of 8.3288 (4) and 8.5220 (4) Å are also present.
Hydrogen bonding is observed with the H atoms of the coordinated water molecule. An intrachain hydrogen bond occurs between atom H21 and nitrile atom N3 (Fig. 1). Adjacent chains are assembled into sheets [parallel to the (111) plane] by interchain hydrogen bonding between atoms H22 and N1.
The large Mn···Mn separation and non-planar geometry of EtO-TCA− in (I) are not conducive to magnetic ordering, and AC (alternating current) susceptibility measurements down to 1.55 K confirmed that no long-range magnetic order occurs in this structure. It is possible that magnetic ordering could occur in a related structure in which the EtO-TCA− anions link transition metals via the nitrile N atoms on the same dicyanomethanide group. This would reduce the superexchange pathway from seven to five atoms and shorten the interchain metal···metal separation by more than an ångstrøm. Such a structure might be formed through the use of organic solvents, which would open the coordination site occupied by water, or by increasing the metal concentration during the crystallization process, thus increasing the chance of coordination to more than two of the four available nitrile N atoms.