Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801013344/dn6002sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536801013344/dn6002Isup2.hkl |
CCDC reference: 172194
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (C-C) = 0.003 Å
- Disorder in main residue
- R factor = 0.032
- wR factor = 0.089
- Data-to-parameter ratio = 25.7
checkCIF results
No syntax errors found ADDSYM reports no extra symmetry
Alert Level C:
PLAT_301 Alert C Main Residue Disorder ........................ 8.00 Perc. PLAT_369 Alert C Long C(sp2)-C(sp2) Bond C(1) - C(1)a = 1.55 Ang.
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
2 Alert Level C = Please check
Ni(NO3)2.6H2O (2.670 g, 9.20 mmol) dissolved in water (20 ml) was added dropwise to a mixture of diethylenetriamine (1.0 ml, 9.20 mmol) of K2C2O4.H2O (0.850 g, 4.60 mmol) in water (30 ml) to give an immediate blue polycrystalline powder. Blue crystals of (I) suitable for X-ray analysis were obtained by recrystallization in hot water.
The diethylenetriamine ligand shows a disordered arrangement of the C6 atom over two positions. Refinement of the site-ocupation factors revealed a partial ocupation close to 0.9 and 0.1, which were kept fixed to this value in the final refinement.
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
[Ni2(C2O4)(C4H13N3)2(H2O)2](NO3)2 | F(000) = 596 |
Mr = 571.80 | Dx = 1.765 Mg m−3 Dm = 1.75 (1) Mg m−3 Dm measured by flotation in a mixture of carbon tetrachloride and bromoform |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 25 reflections |
a = 12.560 (2) Å | θ = 7.5–13.2° |
b = 7.243 (2) Å | µ = 1.83 mm−1 |
c = 13.387 (2) Å | T = 293 K |
β = 117.96 (2)° | Prism, blue |
V = 1075.7 (4) Å3 | 0.40 × 0.40 × 0.25 mm |
Z = 2 |
Enraf Nonius CAD-4 diffractometer | 3495 reflections with I > 2σ(I) |
Radiation source: x-ray tube | Rint = 0.019 |
Graphite monochromator | θmax = 35.0°, θmin = 1.8° |
ω/2θ scans | h = −20→17 |
Absorption correction: empirical (using intensity measurements) via ψ scan (North et al., 1968) | k = 0→11 |
Tmin = 0.494, Tmax = 0.633 | l = 0→21 |
5512 measured reflections | 2 standard reflections every 98 reflections |
4732 independent reflections | intensity decay: 1% |
Refinement on F2 | 13 restraints |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.033 | w = 1/[σ2(Fo2) + (0.0487P)2 + 0.5287P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.089 | (Δ/σ)max = 0.001 |
S = 1.03 | Δρmax = 0.58 e Å−3 |
4732 reflections | Δρmin = −0.73 e Å−3 |
184 parameters |
[Ni2(C2O4)(C4H13N3)2(H2O)2](NO3)2 | V = 1075.7 (4) Å3 |
Mr = 571.80 | Z = 2 |
Monoclinic, P21/n | Mo Kα radiation |
a = 12.560 (2) Å | µ = 1.83 mm−1 |
b = 7.243 (2) Å | T = 293 K |
c = 13.387 (2) Å | 0.40 × 0.40 × 0.25 mm |
β = 117.96 (2)° |
Enraf Nonius CAD-4 diffractometer | 3495 reflections with I > 2σ(I) |
Absorption correction: empirical (using intensity measurements) via ψ scan (North et al., 1968) | Rint = 0.019 |
Tmin = 0.494, Tmax = 0.633 | 2 standard reflections every 98 reflections |
5512 measured reflections | intensity decay: 1% |
4732 independent reflections |
R[F2 > 2σ(F2)] = 0.033 | 13 restraints |
wR(F2) = 0.089 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.03 | Δρmax = 0.58 e Å−3 |
4732 reflections | Δρmin = −0.73 e Å−3 |
184 parameters |
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'s are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles |
Refinement. Refinement on F2 for ALL reflections except for 0 with very negative F2 or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The observed criterion of F2 > σ(F2) is used only for calculating _R_factor_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 | Occ. (<1) | |
Ni1 | 0.55907 (2) | 0.76308 (2) | 0.178205 (14) | 0.02110 (5) | |
O1 | 0.58089 (10) | 1.04120 (13) | 0.14506 (8) | 0.0249 (2) | |
O2 | 0.47092 (10) | 0.76468 (12) | −0.00044 (9) | 0.0254 (2) | |
C1 | 0.53176 (11) | 1.0802 (2) | 0.04158 (10) | 0.0200 (2) | |
O3W | 0.71952 (11) | 0.6948 (2) | 0.17523 (12) | 0.0360 (3) | |
N1 | 0.64163 (13) | 0.8183 (2) | 0.35098 (11) | 0.0315 (3) | |
C2 | 0.5489 (2) | 0.8330 (3) | 0.38839 (14) | 0.0403 (4) | |
H2A | 0.5777 (2) | 0.9115 (3) | 0.45470 (14) | 0.048* | |
H2B | 0.5320 (2) | 0.7118 (3) | 0.40838 (14) | 0.048* | |
C3 | 0.4348 (2) | 0.9145 (3) | 0.2931 (2) | 0.0417 (4) | |
H3A | 0.3697 (2) | 0.9083 (3) | 0.3128 (2) | 0.05* | |
H3B | 0.4481 (2) | 1.0431 (3) | 0.2822 (2) | 0.05* | |
N4 | 0.40125 (12) | 0.8110 (2) | 0.18794 (12) | 0.0295 (2) | |
C5 | 0.3425 (2) | 0.6328 (3) | 0.1840 (2) | 0.0434 (4) | |
H5A | 0.2557 (2) | 0.6476 (3) | 0.1420 (2) | 0.052* | 0.9 |
H5B | 0.3626 (2) | 0.5948 (3) | 0.2603 (2) | 0.052* | 0.9 |
H5C | 0.3074 (2) | 0.6398 (3) | 0.2348 (2) | 0.052* | 0.1 |
H5D | 0.2769 (2) | 0.6158 (3) | 0.1081 (2) | 0.052* | 0.1 |
C6 | 0.3819 (2) | 0.4853 (3) | 0.1287 (2) | 0.0394 (4) | 0.9 |
H6A | 0.3556 (2) | 0.3651 (3) | 0.1406 (2) | 0.047* | 0.9 |
H6B | 0.3459 (2) | 0.5074 (3) | 0.0480 (2) | 0.047* | 0.9 |
N7 | 0.51403 (14) | 0.4891 (2) | 0.17864 (12) | 0.0319 (3) | |
C6A | 0.4150 (16) | 0.4776 (19) | 0.2122 (16) | 0.042 (4) | 0.1 |
H3C | 0.3651 (16) | 0.3710 (19) | 0.1757 (16) | 0.051* | 0.1 |
H3D | 0.4511 (16) | 0.4587 (19) | 0.2933 (16) | 0.051* | 0.1 |
N10 | 0.82822 (14) | 0.8786 (2) | 0.01015 (13) | 0.0363 (3) | |
O11 | 0.75272 (14) | 0.9460 (2) | 0.03687 (13) | 0.0467 (3) | |
O12 | 0.8234 (2) | 0.9207 (4) | −0.07927 (15) | 0.0796 (6) | |
O13 | 0.9063 (2) | 0.7776 (4) | 0.0781 (2) | 0.0932 (8) | |
H31W | 0.781 (2) | 0.679 (4) | 0.237 (2) | 0.049 (7)* | |
H32W | 0.743 (3) | 0.767 (4) | 0.142 (3) | 0.063 (9)* | |
H71 | 0.553 (2) | 0.440 (3) | 0.2473 (16) | 0.048 (6)* | |
H41 | 0.354 (2) | 0.876 (3) | 0.1313 (19) | 0.059 (7)* | |
H72 | 0.532 (2) | 0.431 (4) | 0.133 (2) | 0.054 (7)* | |
H11 | 0.682 (2) | 0.920 (3) | 0.365 (2) | 0.051 (7)* | |
H12 | 0.695 (2) | 0.736 (3) | 0.394 (2) | 0.052 (8)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Ni1 | 0.02101 (8) | 0.02123 (8) | 0.02057 (8) | −0.00034 (6) | 0.00934 (6) | 0.00223 (6) |
O1 | 0.0285 (5) | 0.0237 (4) | 0.0193 (4) | −0.0037 (4) | 0.0085 (4) | 0.0000 (3) |
O2 | 0.0331 (5) | 0.0200 (4) | 0.0225 (4) | −0.0025 (3) | 0.0126 (4) | 0.0005 (3) |
C1 | 0.0187 (5) | 0.0202 (4) | 0.0211 (5) | −0.0007 (4) | 0.0093 (4) | −0.0008 (4) |
O3W | 0.0257 (5) | 0.0456 (6) | 0.0374 (6) | 0.0091 (5) | 0.0152 (5) | 0.0132 (5) |
N1 | 0.0325 (7) | 0.0330 (6) | 0.0232 (5) | −0.0044 (5) | 0.0082 (5) | 0.0022 (5) |
C2 | 0.0475 (10) | 0.0481 (9) | 0.0274 (7) | 0.0034 (8) | 0.0193 (7) | −0.0024 (6) |
C3 | 0.0443 (10) | 0.0440 (9) | 0.0402 (9) | 0.0108 (7) | 0.0225 (8) | −0.0044 (7) |
N4 | 0.0262 (6) | 0.0337 (6) | 0.0295 (6) | 0.0027 (5) | 0.0139 (5) | 0.0022 (5) |
C5 | 0.0351 (9) | 0.0506 (10) | 0.0511 (11) | −0.0116 (8) | 0.0257 (8) | −0.0026 (8) |
C6 | 0.0433 (10) | 0.0354 (8) | 0.0369 (9) | −0.0161 (8) | 0.0167 (8) | −0.0040 (7) |
N7 | 0.0410 (7) | 0.0237 (5) | 0.0317 (6) | 0.0004 (5) | 0.0177 (6) | 0.0017 (4) |
C6A | 0.051 (11) | 0.032 (7) | 0.045 (10) | −0.017 (7) | 0.024 (8) | −0.006 (7) |
N10 | 0.0366 (7) | 0.0385 (7) | 0.0374 (7) | 0.0036 (6) | 0.0204 (6) | 0.0003 (6) |
O11 | 0.0522 (8) | 0.0429 (7) | 0.0623 (9) | 0.0069 (6) | 0.0412 (7) | 0.0024 (6) |
O12 | 0.0843 (14) | 0.123 (2) | 0.0527 (10) | 0.0302 (13) | 0.0494 (10) | 0.0219 (11) |
O13 | 0.087 (2) | 0.109 (2) | 0.091 (2) | 0.0644 (14) | 0.0473 (13) | 0.0509 (13) |
Ni1—O1 | 2.1081 (11) | N4—H41 | 0.85 (2) |
Ni1—O2 | 2.1125 (12) | N7—H71 | 0.888 (19) |
Ni1—O3W | 2.0935 (17) | N7—H72 | 0.86 (3) |
Ni1—N1 | 2.0822 (14) | C1—C1i | 1.5463 (17) |
Ni1—N4 | 2.0758 (18) | C2—C3 | 1.522 (3) |
Ni1—N7 | 2.0641 (15) | C5—C6 | 1.509 (3) |
O1—C1 | 1.2561 (16) | C5—C6A | 1.383 (17) |
O2—C1i | 1.2451 (15) | C2—H2B | 0.97 |
O3W—H32W | 0.83 (4) | C2—H2A | 0.97 |
O3W—H31W | 0.83 (2) | C3—H3A | 0.97 |
O11—N10 | 1.258 (3) | C3—H3B | 0.97 |
O12—N10 | 1.209 (3) | C5—H5A | 0.97 |
O13—N10 | 1.220 (3) | C5—H5D | 0.97 |
N1—C2 | 1.471 (3) | C5—H5B | 0.97 |
N4—C3 | 1.472 (2) | C5—H5C | 0.97 |
N4—C5 | 1.476 (3) | C6—H6A | 0.97 |
N7—C6A | 1.51 (2) | C6—H6B | 0.97 |
N7—C6 | 1.470 (3) | C6A—H3C | 0.97 |
N1—H12 | 0.88 (2) | C6A—H3D | 0.97 |
N1—H11 | 0.87 (2) | ||
O1—Ni1—O2 | 78.89 (4) | O11—N10—O12 | 119.34 (19) |
O1—Ni1—O3W | 90.02 (6) | O11—N10—O13 | 118.04 (19) |
O1—Ni1—N1 | 90.23 (5) | O1—C1—O2i | 126.01 (12) |
O1—Ni1—N4 | 94.34 (6) | O1—C1—C1i | 116.50 (11) |
O1—Ni1—N7 | 169.13 (5) | O2i—C1—C1i | 117.48 (11) |
O2—Ni1—O3W | 88.74 (6) | N1—C2—C3 | 109.14 (15) |
O2—Ni1—N1 | 168.57 (5) | N4—C3—C2 | 109.79 (17) |
O2—Ni1—N4 | 93.50 (6) | N4—C5—C6A | 116.5 (8) |
O2—Ni1—N7 | 90.55 (5) | N4—C5—C6 | 111.32 (19) |
O3W—Ni1—N1 | 94.82 (7) | N7—C6—C5 | 108.87 (17) |
O3W—Ni1—N4 | 175.41 (6) | N7—C6A—C5 | 113.8 (11) |
O3W—Ni1—N7 | 92.32 (7) | C3—C2—H2B | 109.9 |
N1—Ni1—N4 | 83.75 (7) | H2A—C2—H2B | 108.3 |
N1—Ni1—N7 | 100.13 (6) | C3—C2—H2A | 109.8 |
N4—Ni1—N7 | 83.66 (7) | N1—C2—H2A | 109.9 |
Ni1—O1—C1 | 113.68 (8) | N1—C2—H2B | 109.9 |
Ni1—O2—C1i | 113.38 (8) | N4—C3—H3A | 109.7 |
Ni1—O3W—H31W | 117.8 (18) | N4—C3—H3B | 109.7 |
Ni1—O3W—H32W | 117 (3) | C2—C3—H3A | 109.7 |
H31W—O3W—H32W | 103 (3) | C2—C3—H3B | 109.7 |
Ni1—N1—C2 | 109.30 (11) | H3A—C3—H3B | 108.2 |
C3—N4—C5 | 113.18 (16) | N4—C5—H5B | 109.4 |
Ni1—N4—C5 | 109.15 (13) | C6—C5—H5A | 109.4 |
Ni1—N4—C3 | 106.98 (13) | N4—C5—H5C | 108.3 |
Ni1—N7—C6 | 105.65 (12) | N4—C5—H5D | 108.3 |
Ni1—N7—C6A | 108.6 (5) | N4—C5—H5A | 109.4 |
C2—N1—H12 | 107.9 (17) | C6A—C5—H5D | 108.1 |
H11—N1—H12 | 104 (2) | H5C—C5—H5D | 107.4 |
Ni1—N1—H11 | 109.9 (16) | C6—C5—H5B | 109.4 |
Ni1—N1—H12 | 115.3 (15) | H5A—C5—H5B | 108.0 |
C2—N1—H11 | 109.8 (17) | C6A—C5—H5C | 108.0 |
C5—N4—H41 | 108.5 (16) | N7—C6—H6A | 109.9 |
Ni1—N4—H41 | 108.9 (19) | N7—C6—H6B | 109.9 |
C3—N4—H41 | 110.1 (15) | C5—C6—H6A | 109.9 |
C6—N7—H72 | 106.5 (18) | C5—C6—H6B | 109.9 |
Ni1—N7—H71 | 111.7 (14) | H6A—C6—H6B | 108.3 |
Ni1—N7—H72 | 108.3 (19) | N7—C6A—H3D | 109 |
C6—N7—H71 | 114.8 (17) | H3C—C6A—H3D | 108 |
C6A—N7—H71 | 78.5 (19) | C5—C6A—H3C | 109 |
C6A—N7—H72 | 135 (2) | C5—C6A—H3D | 108.8 |
H71—N7—H72 | 110 (2) | N7—C6A—H3C | 109 |
O12—N10—O13 | 122.6 (2) |
Symmetry code: (i) −x+1, −y+2, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H11···O3Wii | 0.87 (2) | 2.53 (2) | 3.343 (2) | 157 (2) |
N1—H12···O11iii | 0.88 (2) | 2.26 (2) | 3.069 (2) | 152 (2) |
O3W—H31W···O1iii | 0.83 (2) | 1.98 (3) | 2.767 (2) | 157 (3) |
O3W—H32W···O11 | 0.83 (4) | 1.96 (3) | 2.764 (2) | 165 (4) |
O3W—H32W···O13 | 0.83 (4) | 2.57 (4) | 3.227 (3) | 138 (3) |
N4—H41···O11i | 0.85 (2) | 2.39 (2) | 3.231 (2) | 170 (3) |
N4—H41···O12i | 0.85 (2) | 2.49 (3) | 3.164 (3) | 137 (2) |
N7—H71···O13iii | 0.89 (2) | 2.45 (2) | 3.301 (3) | 161 (2) |
N7—H72···O2iv | 0.86 (3) | 2.25 (3) | 3.087 (2) | 164 (3) |
Symmetry codes: (i) −x+1, −y+2, −z; (ii) −x+3/2, y+1/2, −z+1/2; (iii) −x+3/2, y−1/2, −z+1/2; (iv) −x+1, −y+1, −z. |
Experimental details
Crystal data | |
Chemical formula | [Ni2(C2O4)(C4H13N3)2(H2O)2](NO3)2 |
Mr | 571.80 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 293 |
a, b, c (Å) | 12.560 (2), 7.243 (2), 13.387 (2) |
β (°) | 117.96 (2) |
V (Å3) | 1075.7 (4) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 1.83 |
Crystal size (mm) | 0.40 × 0.40 × 0.25 |
Data collection | |
Diffractometer | Enraf Nonius CAD-4 diffractometer |
Absorption correction | Empirical (using intensity measurements) via ψ scan (North et al., 1968) |
Tmin, Tmax | 0.494, 0.633 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5512, 4732, 3495 |
Rint | 0.019 |
(sin θ/λ)max (Å−1) | 0.806 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.033, 0.089, 1.03 |
No. of reflections | 4732 |
No. of parameters | 184 |
No. of restraints | 13 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.58, −0.73 |
Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, XCAD4 (Harms & Wocadlo, 1995), SIR92 (Altomare et al., 1993), SHELXL97 (Sheldrick, 1997), ORTEP-3 (Farrugia, 1997), WinGX (Farrugia, 1999).
Ni1—O1 | 2.1081 (11) | Ni1—N1 | 2.0822 (14) |
Ni1—O2 | 2.1125 (12) | Ni1—N4 | 2.0758 (18) |
Ni1—O3W | 2.0935 (17) | Ni1—N7 | 2.0641 (15) |
O1—Ni1—O2 | 78.89 (4) | O2—Ni1—N7 | 90.55 (5) |
O1—Ni1—O3W | 90.02 (6) | O3W—Ni1—N1 | 94.82 (7) |
O1—Ni1—N1 | 90.23 (5) | O3W—Ni1—N4 | 175.41 (6) |
O1—Ni1—N4 | 94.34 (6) | O3W—Ni1—N7 | 92.32 (7) |
O1—Ni1—N7 | 169.13 (5) | N1—Ni1—N4 | 83.75 (7) |
O2—Ni1—O3W | 88.74 (6) | N1—Ni1—N7 | 100.13 (6) |
O2—Ni1—N1 | 168.57 (5) | N4—Ni1—N7 | 83.66 (7) |
O2—Ni1—N4 | 93.50 (6) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H11···O3Wi | 0.87 (2) | 2.53 (2) | 3.343 (2) | 157 (2) |
N1—H12···O11ii | 0.88 (2) | 2.26 (2) | 3.069 (2) | 152 (2) |
O3W—H31W···O1ii | 0.83 (2) | 1.98 (3) | 2.767 (2) | 157 (3) |
O3W—H32W···O11 | 0.83 (4) | 1.96 (3) | 2.764 (2) | 165 (4) |
O3W—H32W···O13 | 0.83 (4) | 2.57 (4) | 3.227 (3) | 138 (3) |
N4—H41···O11iii | 0.85 (2) | 2.39 (2) | 3.231 (2) | 170 (3) |
N4—H41···O12iii | 0.85 (2) | 2.49 (3) | 3.164 (3) | 137 (2) |
N7—H71···O13ii | 0.888 (19) | 2.45 (2) | 3.301 (3) | 161 (2) |
N7—H72···O2iv | 0.86 (3) | 2.25 (3) | 3.087 (2) | 164 (3) |
Symmetry codes: (i) −x+3/2, y+1/2, −z+1/2; (ii) −x+3/2, y−1/2, −z+1/2; (iii) −x+1, −y+2, −z; (iv) −x+1, −y+1, −z. |
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The design and synthesis of oxalato-bridged nickel(II) complexes have attracted much attention during the last few years due to the strong magneto-structural correlations found in this kind of complex (Román et al., 1996; Escuer et al., 1994). In the framework of our current research of polynuclear oxalato-containing first-row transition metal complexes (Castillo et al., 2000, 2001) we have obtained the compound µ-oxalato-bis[aqua(diethylenetriamine)nickel(II)] dinitrate, (I).
The crystal structure of (I) comprises NO3- anions and [Ni2(C2O4)(C4H13N3)2(H2O)2]2+ binuclear cations (Fig. 1) having a symmetry centre at the midpoint of the C—C bond of the oxalate bridge. As observed in related compounds (Travnicek et al., 1997; Román et al., 1996; Escuer et al., 1994), the oxalate ion joins two adjacent coordination polyhedra with its O atoms occupying two cis positions in both polyhedra, and the diethylenetriamine group acts as a facially coordinated tridentate ligand. The coordination geometry around each metal atom is NiN3O3 distorted octahedral, with the O1, O2, N1 and N7 atoms in the equatorial plane [maximum deviation 0.010 (2) Å for N7]; N4 and O3W are on the axial sites. The nickel–nickel separation across the bridging oxalate is 5.487 (1) Å and the Ni–oxalato–Ni fragment is nearly planar. In the crystal structure of (I), complex cations and nitrate anions are held together by means of an extensive three-dimensional network of OW—H···O, N—H···O/OW hydrogen bonds. Magnetic susceptibility data of (I) in the temperature range 1.8–300.0 K show the occurrence of an intramolecular antiferromagnetic interaction with J = -27.2 cm-1 and g = 2.20. The magnitude of the exchange coupling constant is within the range found for oxalate-bridged nickel(II) complexes with a NiN3O3 chromophore.