Synthesis, crystal structure and Hirshfeld surface analysis of a 1D coordination polymer <i>catena</i>-poly[[diaquabis(nicotinamide-κ<i>N</i> <sup>1</sup>)nickel(II)]-μ-fumarato-κ<sup>2</sup> <i>O</i> <sup>1</sup>:<i>O</i> <sup>4</sup>]
Acta crystallographica. Section E, Crystallographic communications